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ORIGINAL ARTICLE

Characterization of biochemical traits, volatile compounds, and sensorial attributes of pistachio (Pistacia vera L.) nuts and oil as affected by regulated deficit irrigation and roasting

Walid Abidi1, Rawaa Akrimi1, Valeria Rizzo2*, Fabrizio Cincotta3, Maria Merlino3, Giuseppe Muratore4

1Regional Center of Agricultural Research of Sidi Bouzid (CRRA), Sidi Bouzid, Tunisia;

2Department of Biosciences and Technology for Food Agriculture and Environment, University of Teramo, Campus Aurelio Saliceti, via Balzarini 1, Teramo, Italy;

3Department of Veterinary Sciences, University of Messina, Polo Universitario dell’Annunziata, Viale G. Palatucci, Messina, Italy

4Department of Agriculture, Food and Environment (Di3A), University of Catania, via S. Sofia 100, Catania, Italy

Abstract

Prolonged drought poses a critical challenge for pistachio cultivation in Mediterranean regions. Water-saving strategies and selecting adapted cultivars can help maintain sustainable production. This study was conducted in the experimental orchard of the Regional Center of Agricultural Research of Sidi Bouzid, Tunisia. Four pistachio cultivars (Mateur, Elguetar, Kerman, and Ohadi) grafted on P. atlantica rootstock were used to investigate the impact of regulated deficit irrigation (RDI) on yield, nut composition, volatile compounds, phenolic compounds, fatty acid profile, and sensory analysis. Three irrigation treatments were applied: control (T0) received 100% crop evapotranspiration (ETc) during all stages of nut development; RDI treatment (T1) received 50% ETc during stages I and II of nut development, followed by 100% ETc during stage III; and stressed treatment (T2) received 50% ETc during two growing seasons (2017 and 2018). Pistachio nuts were immersed in a solution of NaCl (5% w/v) for 5 min and then introduced in an oven for 2 h at 120ºC to obtain ‘roasted’ pistachio for volatile and sensorial analysis. Results showed that RDI saved 20% of irrigation water during stages I and II of nut development while maintaining similar yield, nut composition, and fatty acid profile as that of control. Moreover, the volatile compounds content and oil yield were enhanced under drought stress. Roasting enhanced the perception of volatile compounds, especially nitrogenous ones. Cultivars Mateur and Ohadi showed high sensory quality, with Ohadi achieving the highest consumer satisfaction despite lower yield and dehiscence rate. Cultivar Mateur was suitable for high-density planting in semiarid environments. Overall, RDI proved effective for increasing water use efficiency without compromising pistachio quality, suggesting its suitability for arid and semiarid orchards.

Key words: nut quality, pistachio, regulated deficit irrigation, roasting, volatile compounds

*Corresponding Author: Valeria Rizzo, Department of Biosciences and Technology for Food, Agriculture and Environment, University of Teramo, Campus Aurelio Saliceti, via Balzarini 1, 64100 Teramo, Italy. Email: [email protected]

Academic Editor: Prof. Monica Rosa Loizzo -Università della Calabria, Italy

Received: 26 August 2024; Accepted: 13 October 2024; Published: 1 January 2025

DOI: 10.15586/ijfs.v37i1.2814

© 2025 Codon Publications
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0). License (http://creativecommons.org/licenses/by-nc-sa/4.0/)

Introduction

Pistachios are among the most nutritious nuts consumed as raw or roasted, with or without salt (Dini et al., 2019). The pistachio tree has the reputation of being drought-tolerant and saline-resistant species cultivated under rainfed conditions in its region of origin (Rieger, 1995). In Tunisia, pistachio production is around 3,190 tons with a cultivation area of 27,153 hectates (ha) (FAOSTAT, 2024). Recently, extension of pistachio cultivation has taken place in west-central Tunisia because of economic importance of pistachio nuts. New pistachio orchards are planted under high-density system, which increases water requirement. However, water availability for agriculture continues to decline due to changes in global climactic conditions. Therefore, great emphasis is placed on irrigation management in arid regions to increase water use efficiency (Abboud et al., 2019). Regulated deficit irrigation (RDI) is a system of managing water supply by imposing water deficits in specific phenological stages, which are found to be less sensitive, without loss of economic benefits (Carbonell-Barrachina et al., 2015). In pistachio production, development of nuts is characterized by three different periods (Goldhamer, 1995): stage I starts at the beginning of nut growth and ends when its maximum size is reached; during stage II, hardening of shells takes place; and finally, stage III is the period of kernel growth.

Pistachios are also considered functional food on account of their high contents of monounsaturated fatty acids, vitamins, minerals, sterols, polyphenols, and high antioxidant potential (Hojjati et al., 2013; Satil et al., 2003). Pistachio nuts contain about 50% of oil, with maximum of oleic acid (54.4–71.8%), linoleic acid (16.7–35.3%), palmitic acid (7.2–10.5%), stearic acid (0.9–10.5%), and linolenic acid (up to 2%) (Arena et al., 2007). These fatty acids have important therapeutic properties, such as reducing triacylglycerols, low-density cholesterol (LDL), total cholesterol, and glycemic index (Taghizadeh et al., 2018). Among different nuts, extraction of oil is an interesting alternative due to their high lipid content, such as almonds (53%), pistachios (50%), and walnuts (65%) (Sena-Moreno et al., 2015). Nutrient oil is used in the food and cosmetics industry, adding value to products.

Raw nuts, even if well appreciated, have a rather bland aroma, because of some compounds that are responsible for characteristic flavor generated during the roasting process (Aceña et al., 2010). Roasting is a key method in pistachio processing used to enhance sensory properties and aroma attributes of nuts influencing consumer’s acceptance (Aceña et al., 2011). It was reported that roasting of pistachio nuts increased free fatty acids, reduced total available carbohydrates, decreased moisture of nuts, produced a more crispy and fragile texture, enhanced Maillard reaction and degradation of lipids, and created desirable pigments and aroma compounds (Hojjati et al., 2013).

In this context, the present study was conducted to analyze the impact of RDI on pistachio nuts and oil bioactive compounds, volatile compounds, and sensorial analysis after the roasting process of cultivars Mateur, Elguetar, Kerman, and Ohadi grown under semiarid conditions.

Material and Methods

Plant material

The trial was carried out in the Regional Center of Agriculture Research (CRRA, Sidi Bouzid) in west-central Tunisia (9º43’ E, 35º01’ N; altitude 354 m) during the growing seasons of 2017 and 2018. Age-wise, 17-year-old pistachio trees of cultivars (cv.) Mateur, Elguetar, Kerman, and Ohadi grafted on P. atlantica rootstock were studied. Trees were trained to the standard open vase system planted at a spacing of 6 × 6 m, and grown under standard conditions of fertilization, pruning, pollination, pest, and disease control. The surveyed trees were selected for uniform trunk and canopy size.

Experimental design

The trial was set in a complete randomized block design arrangement. The area assigned for the experiment was divided into three main blocks corresponding to each irrigation treatment (T0 = 100% ETc: irrigation at full water requirements; treatment T1 = RDI: irrigation at 50% water requirements during stages I and II of nut development, and 100% ETc during stage III; and treatment T2 = 50% ETc: irrigation at 50% water requirements). Each main block was then divided into four experimental units, one for each cultivar. Each cultivar (experimental plot) had on nine trees (eight females and one male). Experimental area had semiarid Mediterranean climate with a low annual rainfall of 200 mm irregularly distributed over the growing season and a reference evapotranspiration (ETo) of 1,400 mm. The soil was aridisol, with a sandy-clay texture (clay = 13.69%, silt = 1.11%, and sand = 84.7%), 10% active CaCO3, basic pH of 8.6, and slightly saline concentration (3.6 dS/m). The irrigation water was slightly saline and had a high concentration of nitrate (EC = 1.5 dS/m; SAR = 2.4; NO3 = 50 ppm; pH = 7.9; and HCO3 = 16.0 meq-1) (Akrimi et al., 2020).

Applied treatments

Regulated deficit irrigation treatments

The treatments consisted of three different irrigation regimes (Table 1) during the two growing seasons. The phenological stages considered during RDI treatments were those suggested by Goldhamer and Beede (2004)—stage I: from sprouting until the end of rapid nut growth; stage II: from maximum nut size until the beginning of kernel growth; and stage III: from the beginning of kernel growth until harvest.

Table 1. Crop evapotranspiration rate (ETc) and irrigation regimes applied to the control (treatment T0), RDI (treatment T1), and stressed (treatment T2) during the growing season 2017–2018.

Water applied (mm)
Treatment Year
2017 2018
Stage I Stage II Stage III Stage I Stage II Stage III
ETc T0 78.9 64.4 101.9 57.5 53.0 107.5
ETt1 T1 39.4 32.2 101.9 28.7 26.5 107.5
ETt2 T2 39.4 32.2 50.9 28.7 26.5 53.7
Rainfall (mm) 112.9 9.4 16.6 58.6 3.6 48.6
ET0 (mm) 443.2 293.6 446.9 324.2 242.8 471.5

ETc: Crop evapotranspiration rate; ETt1: evapotranspiration rate under regulated deficit irrigation; ETt2: evapotranspiration rate under stressed treatments; ET0 : reference evapotranspiration of annual rainfall; Treatment: T0: well watered; T1: regulated deficit irrigation; T2: stressed; stage I: from sprouting until the end of rapid nut growth; stage II: from maximum nut size until the beginning of kernel growth; stage III: from the beginning of kernel growth up to harvest.

The applied treatments were as follows:

  • Treatment (T0): trees received water to cover estimated evapotranspiration losses (100% ETc), also referred to as ‘control’;

  • Treatment (T1): trees received 50% ETc during stages I and II, and 100% ETc during stage III, also referred to as ‘RDI’;

  • Treatment (T2): trees received 50% ETc during the growing season, also referred to as ‘stressed’.

Drip irrigation was applied for 3 days every week, and was controlled and adjusted weekly according to the potential of soil matrix measured by tensiometers located 0.5 m from the drip head at depths of 30 cm and 60 cm. A drip line was utilized in each tree row, with four self-compensating drippers (4 L/h) per tree, 0.5 m apart. The amount of provided water was calculated based on crop ETc and crop coefficient (Kc) according to the FAO method: ETc = ETo × Kc (Allen et al., 1998). The mean Kc values provided by Goldhamer (1995) were used: 0.39, 1.06, and 1.14 for stages I, II, and III, respectively.

Roasting treatments

After manual nut peeling, pistachio nuts were immersed in NaCl (5% w/v) solution for 5 min. Salted nuts were left to dry at room temperature for 30 min to release the excess of water and then kept in an oven for 2 h at 120ºC to obtain ‘roasted’ pistachio for volatile and sensorial analysis (Figure 1).

Figure 1. Outline of pistachio preparation phases for roasting and subsequent analyses.

Agronomical and pomological traits

Nuts were handpicked at commercial maturity and assessed by color of shells and dehiscence of nuts (Figure 2).

Figure 2. Pistachio nuts of the studied cultivars (M: Mateur, K: Kerman, E: Elguetar, and O: Ohadi).

Yield (in kg) was determined per tree. At harvest, a representative nut sample (100 nuts) was taken for pomological evaluations. Nut characteristics, such as mean nut weight (NW in g) and 100 kernel weight (g), were calculated using an electronic balance of 0.001-g sensitivity; split nuts (%), blank production (%), and infested nuts were evaluated. Nut dimensions and morphological and quality parameters of kernels were carried out at random on a sample of 100 nuts collected from trees. The color of crunched pistachios (Figure 3) was measured using a Konica Minolta CR-400 colorimeter (Tokio, Japan) to obtain CIE L*, a*, and b* chromatic coordinates.

Figure 3. Color determination of pistachio nuts collected from the studied cultivars.

Nutritional quality of pistachio nuts

Composition of pistachio nuts

The moisture content was determined with milled pistachio nuts at 105°C for 6 h in an oven (Memmert, Model UNE 400 PA; Scheabach, Germany) (Chahed et al., 2008). The ash content was determined by muffle furnace at 550°C. Concentration of proteins was determined according to the method from Bradford (1976) using bovine serum albumin (BSA) as a standard. Total protein content was expressed as mg g-1 of fresh weight (FW). The fiber content was determined according to Ashraf et al. (2011), and the fat content (FC) was determined using hexane as a solvent (Association of Official Analytical Chemists [AOAC], 1995). After calculating the moisture, ash, protein, fat, and crude fiber content in the form of a powder, the total carbohydrate content was determined using the following formula:

Total carbohydrates = 100 – (moisture [%] + ash [%] + protein [%] + fat [%] + crude fiber [%]).

Analyses were made in triplicate and the results were expressed as a percentage of grams of FW (% g-1). Oil yield is defined as the quotient of the weight of extracted oil and the weight of pistachio nut powder, and is expressed as percentage (%) (Uquiche et al., 2008). Oil extraction was accomplished by solvent extraction technique using n-hexane according to the method described previously (Damirchi et al., 2005). The prepared samples were kept at –20°C for further analysis.

Oil yield was determined using the weight of the oil extracted from 100-g pistachio samples. Free acidity was expressed as oleic acid (g 100 g-1 oil), and UV absorption characteristics (K232 and K270) were determined according to the International Olive Council (Conseil Oléicole International [IOC], 2015), while the refractive index (RI) was calculated according to the AOAC (2000) method. Carotenoid and chlorophyll from oil samples were extracted with cyclohexane, and their contents were determined according to the method described by Minguez-Mosquera et al. (1991). Pigments were measured at 470 nm and 670 nm, while the color of crunched pistachios was determined as described previously for nuts.

Content of bioactive compounds in pistachio nuts and oil

Samples were crunched to form powder in a mortar and pestle, separately. By weight, 20 g of pistachio kernel of each cultivar was extracted with 200 mL of 95% methanol for 48 h at room temperature. Then, the extracts were filtered and evaporated at low pressure; samples were stored at -20°C until analysis (Taghizadeh et al., 2018). Total anthocyanin content (TAC) was evaluated by measuring absorbance at 535 nm and 700 nm in hydroalcoholic extract (Fuleki and Francis, 1968). Concentration of anthocyanins was calculated using the molar extinction absorptivity coefficient Ɛ = 25,965/cm M and was expressed in mg of cyanidin 3-glucoside equivalents (C3Geq) per kilogram of dry weight (C3Geq/kg DW). Total flavonoid content (TFC) was measured as described by Huang et al. (2004). Briefly, 5 mL of 2% aluminum trichloride (AlCl3) in methanol was mixed with the same volume of extract. Absorbance was read at 367 nm and the TFC was determined by a standard curve plotted for catechin. Results were expressed as mg of catechin equivalents (mg CE/g). Total phenol content (TPC) was determined using the Folin–Ciocalteu method (Abidi et al., 2011). For this purpose, 100 μL of extract was mixed with 0.5-mL Folin–Ciocalteu reagent. Then, 7 mL of distilled water was added to the solution. After 5 min incubation at room temperature, 1.5 mL 10% sodium bicarbonate (Na2CO3) solution was added to the mixture and left in the dark for 2 h. Absorbance was read at 725 nm against blank and results were presented as mg gallic acid equivalence for 100 g of DW (mg GAE/100 g DW). Total phenols (TP) and antioxidant capacity (AC) of pistachio oil extracts were measured as described for pistachio nuts.

Antioxidant capacity of pistachio nuts and oil

The antioxidant capacity of pistachio methanolic extracts was evaluated using modified 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), ferric reducing/antioxidant power (FRAP), and β-carotene bleaching (β-carot) activity assays. The DPPH assay was performed using the method adapted from Brand-Williams et al. (1995). In brief, 0.1-mM solution of DPPH in methanol was prepared and 2.9 mL of the solution was added to 0.1 mL of extract. The mixture was shaken vigorously for about 10 s and incubated in the dark at room temperature for 10 min; the absorbance was recorded at 515 nm against a blank (50 μL of sample with 950 μL of ethanol 80%). The control was a mixture of DPPH (950 μL) plus ethanol 80% (50 μL). A standard curve was drawn with Trolox (0.5–10 ppm). Results were expressed as µg of Trolox equivalence (TE) per gram of DW.

The FRAP assay was performed using 2,4,6-tripyridylS-triazine (TPTZ) solution according to the method described by Fu et al. (2020). In brief, 4.9 mL of FRAP solution (2.5 mL of 0.1-M acetate buffer [pH = 3.6], 250 µL of 10-mM TPTZ, and 250 µL of 20-mM FeCl3) was mixed with 0.1 mL of sample extract. Thereafter, the obtained mixture was shaken vigorously and incubated in the dark for 10 min at room temperature. Finally, the absorbance was measured at 593 nm. Results were calculated using a Trolox standard curve and expressed as µg of TE per gram of DW.

β-carot activity was determined using the method described by Kim et al. (2019). A mixture of 20-μL linoleic acid and 100-μL Tween 20 was dissolved in 10-mL chloroform. After removing chloroform, 10 mL of distilled water was added and stirred vigorously. Then, 240 μL of emulsion was mixed with 10 μL of extracts at various concentrations (1, 2, 3, 4, and 5 mg/mL) or butylated hydroxytoluene (BHT) as a positive control. The absorbance was measured every 15 min for 120 min at 470 nm. The antioxidant activity of extracts in terms of β-carot was calculated using the following formula:

βcarotBA%=1Abs0 sampleAbs120 sampleAbs0 carotAbs120 sample×100

Content of volatile compounds

The volatile aroma compounds of raw and roasted pistachio nuts from each cultivar were extracted and analyzed by Head Space–Solid Phase Micro-Extraction–Gas Chromatography–Mass Spectrometry (HS-SPME-GC-MS) using the method suggested by Aceña et al. (2010) with slight modifications. Briefly, 1 g of finely crunched pistachio samples was placed into a 40-mL glass vial with 18 mL of NaCl saturated aqueous solution and sealed with a ‘mininert’ valve (Supelco; Bellefonte, PA, USA). Each sample was equilibrated for 30 min at 50°C with continuous stirring (700 rpm) in a thermostatic bath. Then, a divinylbenzene–carboxen-polydimethylsiloxane (DVB/CAR/PDMS) 2-cm fiber with 50/30-µm thickness, purchased from Supelco (Bellfonte, USA), was exposed for 1 h at 50°C in a vial headspace for the extraction of volatile compounds. After extraction, the fiber was inserted into the injection port of GC for the thermal desorption of analyte at 260°C for 3 min. The fiber was conditioned before use and thermally cleaned after each analysis at 250°C in the injector port of GC. A Shimadzu GC 2010 Plus gas chromatograph directly interfaced with a TQMS 8040 triple quadrupole mass spectrometer (Shimadzu; Milan, Italy) was used for GC-MS analysis. Two capillary columns of different polarity were used: (1) VF-WAXms, 60 m, 0.25-mm i.d., 0.25-μm film thickness polar column (Agilent Technologies Italia S.p.A., Milan, Italy) and (2) DB-5 ms, 30 m, 0.25-mm i.d., 0.25-μm film thickness polar column (Agilent Technologies).

The GC conditions were as follows—injector temperature, 260°C; injection mode, splitless: (1) oven temperature VF-WAXms, 45°C held for 5 min, then increased from 80°C at a rate of 10°C/min to 210°C at a rate of 2°C/min and 240°C at 20°C/min; (2) oven temperature SLB-5ms, 60°C to 110°C at a rate of 2°C/min, from 110°C to 160°C at a rate of 3°C/min, and from 160°C to 260°C at a rate of 10°C/min; carrier gas, helium at a constant flow of 1 mL/min; transfer line temperature, 250°C; acquisition range, 40–400 mz-1; and scan speed, 1,250 amu/s. Each compound was identified using mass spectral data, NIST’ 20 (NIST/EPA/NIH Mass Spectra Library, version 2.0, NanoTech Analysis, Turin; Italy) and FFNSC 3.0 database, linear retention indices (LRI) according to the equation of Van Den Dool and Kratz (1963), literature data, and the injection of available standards, as reported previously (Cincotta et al., 2018). The samples were analyzed in duplicate. The compounds were quantified using peak area, and average value was calculated.

Profile of fatty acids

The fatty acid composition of oils was analyzed using GC to determine fatty acid methyl esters (FAMEs), following the method outlined in Ghrab et al. (2010). FAMEs were prepared by saponification/methylation with sodium methylate according to the European Union Commission modified Regulation EEC 2568/91. A capillary column (30-m length and 0.32-mm i.d.; Stabilwax; Restek, Bellefonte, PA, USA) coated with a stationary phase formed by carbowax (0.25-mm thickness) in GC (Shimadzu GC-17A; Japan) was used. The analytical conditions were as follows: flame ionization detector (FID), nitrogen as vector gas at a flow rate of 1 mL/min. The column temperature was isothermal at 180°C and the injector and detector were at 230°C and 250°C, respectively. In all, ten fatty acids were identified by comparing retention times with standard compounds: palmitic acid (C16:0), palmitoleic acid (C16:1), margaric acid (C17:0), heptadecenoic acid (C17:1), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), linolenic acid (C18:3), arachidic acid (C20:0), and gadoleic acid (C20:1).

Sensorial analysis of pistachio nuts

This analysis was performed with salted and roasted pistachio nuts of the four studied varieties grafted on P. atlantica rootstock and conducted with three irrigation treatments of RDI. The sensory study was performed as suggested previously (Carbonell-Barrachina et al., 2015; Noguera-Artiaga et al., 2020). A consumer panel was carried out with 60 consumers selected from personal staff and students of the Faculty of Science of Sidi Bouzid (Tunisia) to study the sensory properties of pistachios. Consumers were aged 20–60 years and had no diet restrictions or allergies for any type of nut. In all, 74% of panelists were women, and 65% were aged between 20 and 35 years, 20% between 35 and 50 years, and 15% were aged between 50 and 65 years. Ten pistachio nuts were served at room temperature to each panelist in an odor-free disposable 60-mL covered plastic cups coded using two-digit numbers. Unsalted crackers and drinking water were used between samples to clean panelists’ palate. Natural illumination was used during the test, and the temperature of the testing room was 20ºC ± 2°C. Panelists responded using a 9-point hedonic scale, where 9 = like extremely and 1 = dislike extremely; they were asked to indicate their order of preference for samples and mark reasons for their preferences regarding the attributes under study (color, hardness, size, roasted and sweet/almond odor, sweet and sour taste, and global satisfaction).

Statistical analysis

All traits were measured or scored for each treatment separately during the two growing seasons. Mean values and mean standard error (SE) were calculated for each studied trait using SPSS 20.0 (SPSS Inc., Chicago, IL). Analysis of variance (ANOVA) was used to test the effects of water treatments and roasting on the studied parameters, and the significance was expressed as p < 0.05. The test Scheffe one ANOVA factor was used to compare means values. Pearson’s correlation at 5% level of significance was performed between antioxidants and antioxidant capacity using the software SPSS 20. Principal components analysis (PCA) of all studied traits was carried out using SPSS 20.0. Component matrix was evaluated and orthogonal factors were rotated using variance maximization (Varimax).

Results

Agronomical parameters

During the 2-year experimental period, results showed significant differences (p < 0.05) between cultivars concerning yield (Table 2). Low yield was observed in treatment T2 whereas treatments T0 and T1 presented the same behavior. The highest yield (7.5 kg/tree) with control treatment was observed for cv. Mateur, followed by cv. Kerman (6.4 kg/tree) and Elguetar (5.1 kg/tree) whereas cv. Ohadi showed the lowest yield (3.8 kg/tree). Results showed that the RDI treatment presented a similar yield as that observed with control treatment when 20% of water was saved during stages I and II of fruit development that increased water productivity. In this sense, Galindo et al. (2018) reported that RDI could benefit water productivity by increasing irrigation water savings, minimizing or eliminating negative impacts on yield and crop revenue, and even improving harvest quality. Findings of the present study agreed with the study conducted by Memmi et al. (2015), reporting that the water restriction applied to pistachio trees at stages I and II of nut development did not affect the final yield. Nut’s FW showed different patterns depending on the genotype. Hence, cv. Ohadi with full irrigated regime (T0) showed the highest nut FW (0.77 g) whereas the lowest value (0.44 g) was shown in cv. Elguetar. Nut weight was not affected by irrigation strategy. These findings were in accordance with the study conducted by Carbonell-Barrachina et al. (2015), reporting that the RDI treatment did not significantly affect the weight of whole pistachio, its edible portion, and its shell.

Table 2. Agronomical and pomological traits of four pistachio cultivars grown under RDI treatments.

Traits Mateur Kerman Elguetar Ohadi
T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2
Yield 7.1 ± 1a,A 6.4 ± 2a,A 5.1 ± 1b,A 6.4 ± 2a,A 5.4 ± 2b,B 4.8 ± 1b,A 5.1 ± 1a,B 4.7 ± 3a,B 4.0 ± 2b,B 3.8 ± 1a,C 3.1 ± 1b,C 2.1 ± 3c,C
WP 0.6 ± 0.1a,A 0.8 ± 0.2a,A 0.5 ± 0.1b,A 0.6 ± 0.1a,A 0.7 ± 0.2a,A 0.5 ± 0.1a,A 0.7 ± 0.2a,A 0.6 ± 0.2a,A 0.5 ± 0.1b,A 0.4 ± 0.2a,B 0.3 ± 0.2a,B 0.2 ± 0.1b,B
NFW 0.6 ± 0.1a,A 0.6 ± 0.5a,A 0.6 ± 0.4a,B 0.4 ± 0.4a,A 0.5 ± 0.5a,A 0.4 ± 0.5a,C 0.6 ± 0.1a,A 0.6 ± 0.6a,A 0.5 ± 0.1a,C 0.8 ± 0.1a,A 0.8 ± 0.1a,A 0.8 ± 0.4a,A
NDW 0.5 ± 0.1a,A 0.5 ± 0.5a,A 0.5 ± 0.4a,B 0.3 ± 0.4a,A 0.3 ± 0.7a,B 0.3 ± 0.4a,C 0.5 ± 0.1a,A 0.4 ± 0.7a,A 0.3 ± 0.1a,C 0.6 ± 0.1a,A 0.6 ± 0.1a,A 0.7 ± 0.4a,A
L 17.8 ± 2a,A 17.4 ± 1a,A 17.1 ± 1a,A 18.2 ± 1a,A 18.1 ± 1a,A 17.9 ± 1a,A 14.8 ± 2a,B 14.4 ± 1a,B 14.1 ± 1a,B 18.2 ± 1a,A 18.1 ± 1a,A 17.9 ± 1a,A
l 9.1 ± 1a,A 9.1 ± 1a,A 9.0 ± 1a,A 10.6 ± 1a,A 10.4 ± 1a,A 10.1 ± 1a,A 8.1 ± 1a,B 8.1 ± 1a,B 8.0 ± 1a,B 11.6 ± 1a,A 11.4 ± 1a,A 11.1 ± 1a,A
H 7.9 ± 1a,A 7.7 ± 1a,A 7.5 ± 1a,B 8.9 ± 1a,A 8.8 ± 1a,A 8.7 ± 1a,A 6.8 ± 1a,B 6.7 ± 1a,B 6.5 ± 1a,B 10.9 ± 1a,A 10.8 ± 1a,A 10.7 ± 1a,A
Split nut 76 ± 5a,A 70 ± 3a,A 68 ± 4b,A 70 ± 3a,A 65 ± 2a,A 72 ± 3a,A 71 ± 5b,A 75 ± 2a,A 70 ± 3b,A 55 ± 6a,B 48 ± 4b,B 46 ± 2b,B
Blanks 7 ± 2c,B 12 ± 2b,B 19 ± 1a,B 10 ± 3b,B 12 ± 3b,B 18 ± 2a,B 9 ± 3c,B 13 ± 3b,B 16 ± 2a,B 25 ± 5c,A 29 ± 2b,A 35 ± 2a,A
Infested 6 ± 1b,A 7 ± 2b,A 10 ± 1a,A 5 ± 2b,A 4 ± 2b,A 7 ± 1a,A 6 ± 2b,A 7 ± 2b,A 11 ± 3a,A 5 ± 2a,A 4 ± 1b,A 7 ± 2a,A

Notes. Values are means (n = 3) ± SE (mean standard error). Different superscripted lowercase letters a, b, and c indicate difference (p < 0.05) among three irrigations treatments (T0: control; T1: regulated deficit irrigation; T2: stressed) in the same cultivar. Superscripted uppercase letters A, B, and C indicate differences (p < 0.05) among cultivars in the same treatment.

Yield: kg/tree; WP = water productivity (kg /m3); NDW = nut dry weight (g); NFW = nut fresh weight (g); L = length (mm); l = width (mm); and H = thickness (mm).

Pomological parameters

Pomological parameters showed statistically significant differences (p < 0.05) between stated cultivars (Table 2). The physical properties of nuts revealed that cv. Ohadi had the highest dimensions of length, L (18.2 mm) and width, l (11.6 mm). Ohadi nuts were thicker, larger, and longer than three other cultivars whereas the kernel of cv. Elguetar had the lowest dimensions (L = 14.8 mm, and l = 8.1 mm). In an experiment conducted in Tunisia, Ghrab et al. (2004) reported that cv. Ohadi produced nuts with a higher weight and a larger size. Nut dimensions presented significant differences between cultivars, mainly explained by the genotype. Carbonell-Barrachina et al. (2015) reported that the size of pistachio nuts was not affected by the RDI irrigation treatment. Cv. Mateur, Kerman, and Elguetar recorded the highest split nut rate of fruit dehiscence (76%, 70%, and 71%, respectively, with control treatment; Table 2). Cv. Ohadi showed the lowest split nut rate (55% with treatment T0, 48% with treatment T1, and 46% with treatment T2) and the highest rate (25%) of blanks. The split and blank proportions of nuts were also affected by the genotype. Present results were in accordance with Zribi et al. (2006), showing that cv. Ohadi presented a low split proportion of 49% whereas cv. Mateur had the higher split proportion (67%). Ghrab et al. (2004) reported that the high proportion of non-split nuts observed between cv. Ohadi and other varieties could be due to the cultivar and the season. The proportion of blanks was higher under stressed treatment (T2). These results were in accordance with the findings of Galindo et al. (2018), reporting that irrigation increased yield, nut size, and splitting, and reduced alternate bearing pattern and incidence of blank nuts. An explanation of blanks proportion in pistachio nuts could be attributed to lack of pollination, poor nutrition, rainfall during anthesis, and water deficit during seed development (Crane and Iwakiri, 1981). Present results showed lower proportions of infested nuts under different irrigation regimes. The observed fungal decay and insect infestation of the kernel was generally low in the present conditions.

Nut color parameters (L*, a*, b*, and C*) presented statistically significant differences (p < 0.05) among genotypes (Figure 4). L* varied from 40.7 in cv. Ohadi to 43.5 in cv. Kerman with control treatment. The a* value ranged from 22.9 in cv. Elguetar to 28.4 in cv. Mateur. The b* value ranged from 16.9 in cv. Mateur to 21.5 in cv. Elguetar. Similar results were reported by Carbonell-Barrachina et al. (2015) and Galindo et al. (2015), stating that the RDI treatments applied did not significantly affect pistachio nut color.

Figure 4. Variation in nut color from the pistachio cultivars (C) under irrigation treatments (T). L* means the brightness of the sample while a* and b* represent color directions, and C* = chroma. Values are mean values of three measurements (n = 3) ± SE. Different letters a, b, and c indicate significant differences between the storage periods of each cultivar (NS: not significant; *p < 0.05, **p < 0.01) according to Duncan’s multiple range test.

Regarding the effect of water regimes on pistachio nut color, results of the present study were in accordance with Guerrero et al. (2005), showing that irrigation increased kernel weight but did not show significant impact on shell and kernel colors. The obtained values in the present study were consistent with those observed by Dini et al. (2019), studying the kinetics of color degradation, chlorophylls, and xanthophylls loss in pistachio nuts during roasting.

Composition of Nuts

Nut composition (moisture, carbohydrates, ash, protein, fiber, and oil yield) varied between cultivars, depending on RDI treatments (Table 3). Hence, treatment T2 presented significant (p < 0.05) lower values of carbohydrates, compared to the control and RDI treatments. Ash content also decreased under stressed treatment (T2), showing a statistically significant (p < 0.05) difference between cv. Mateur, Kerman, and Ohadi. The protein content ranged from 18.6% in cv. Mateur to 25.1% in cv. Ohadi. This trait was also affected by water restriction, showing significant (p < 0.05) lower values with treatment T2. The fiber content presented a similar trend showing significantly lower values with treatmentr T2 whereas treatments T0 and T1 presented the same content. Moisture in nuts decreased with decrease in water supply, showing significant (p < 0.05) lower values under stressed treatment T2.

Table 3. Nut composition (%) for the studied pistachio cultivars grown under RDI treatments.

Traits Mateur Elguetar Kerman Ohadi
Carbohydrates T0 9.20 ± 2a,A 8.70 ± 1a,B 7.80 ± 2a,B 10.20 ± 1a,A
T1 8.10 ± 2a,A 8.10 ± 1a,A 7.23 ± 2a,B 9.83 ± 1a,A
T2 7.85 ± 2b,B 7.73 ± 1b,B 7.00 ± 2b,B 9.35 ± 1b,A
Ash T0 0.50 ± 0.2a,A 0.43 ± 0.1a,B 0.46 ± 0.1a,B 0.52 ± 0.1a,A
T1 0.45 ± 0.2a,A 0.37 ± 0.1b,B 0.45 ± 0.1a,A 0.48 ± 0.1a,A
T2 0.36 ± 0.2b,B 0.40 ± 0.1a,A 0.38 ± 0.1b,B 0.42 ± 0.1b,A
Proteins T0 20.5 ± 0.1a,B 22.5 ± 0.1a,A 21.4 ± 0.1a,B 25.1 ± 0.2a,A
T1 19.3 ± 0.1a,B 20.1 ± 0.1a,B 20.4 ± 0.1a,B 23.1 ± 0.2a,A
T2 18.6 ± 0.1b,B 19.5 ± 0.1b,B 19.1 ± 0.1b,B 22.3 ± 0.2b,A
Fiber T0 1.23 ± 0.5a,B 1.35 ± 0.2a,B 1.52 ± 0.5a,A 1.60 ± 0.2a,A
T1 1.20 ± 0.5a,B 1.15 ± 0.2b,B 1.34 ± 0.5a,A 1.56 ± 0.2a,A
T2 1.13 ± 0.5b,B 1.05 ± 0.2b,B 1.12 ± 0.5b,B 1.21 ± 0.2b,A
Moisture T0 28.26 ± 0.6a,B 29.94 ± 0.5a,A 30.07 ± 0.6a,A 35.61 ± 0.1a,A
T1 24.52 ± 0.4b,B 30.16 ± 0.4a,A 29.47 ± 1.0a,A 33.54 ± 0.6a,A
T2 22.92 ± 0.5b,B 24.66 ± 0.7b,B 26.41 ± 0.9b,B 32.1 ± 0.6b,A
Oil yield (%) T0 54.45 ± 0.3a,A 53.62 ± 0.2a,A 56.63 ± 0.1a,A 46.84 ± 0.3b,B
T1 54.07 ± 0.9a,A 52.77 ± 0.2a,A 55.76 ± 0.3a,A 54.45 ± 0.3a,A
T2 54.38 ± 0.3a,A 53.24 ± 0.1a,A 57.11 ± 0.3a,A 47.57 ± 0.2b,B

FW: fresh weight; DW: dry weight, FC: fat content.

Data are presented as mean ± SE (n = 3). Different superscripted lowercase letters a, b, and c indicate difference (p < 0.05) among three irrigation treatments (T0: control; T1: regulated deficit irrigation; and T2: stressed) in the same cultivar. Uppercase superscripted letters A and B indicate differences (p < 0.05) among cultivars in the same treatment. Mean separation within columns by Scheffe´s test (p ≤ 0.05). In each column, values with the same letter are not significantly different.

Regarding oil yield, cv. Mateur, Elguetar, and Kerman presented similar values under three water regimes. Cv. Ohadi presented higher oil content under RDI treatment, showing a significant difference between treatments T0 and T2. These results were in accordance with those reported by Carbonell-Barrachina et al. (2015), stating that the nuts from treatment T1 showed the highest oil content, followed by control and treatment T2. Yahyavi et al. (2020) reported that differences in oil contents of pistachio cultivars could be due to differences in factors, such as growing conditions, harvesting, and climate.

As expected, irrigation regimes significantly affected nut composition, except for oil yield, which was consistent with water treatments. Nut composition identified cv. Ohadi with high carbohydrates, ash, protein, fiber, and moisture contents. In the present study, nut composition was affected by drought stress, showing lower contents in treatment T2. Kola et al. (2018) reported that irrigation increased crude fiber, ash, and oil contents of pistachio nuts, but decreased protein content. Oil yield showed the same pattern under three water regimes, showing that water restriction did not affect oil content.

Biochemical parameters of nuts

Contents of anthocyanins, flavonoids, and total phenolics and the antioxidant capacity of pistachio nuts are shown in Table 4. Treatments T0 and T1 presented the same values of anthocyanins, flavonoids, total phenols, and RAC, showing statistically significant differences (p < 0.05) with treatment T2. Cv. Elguetar showed low flavonoid content, compared to other three cultivars. Cv. Mateur presented high TPC (410.5 mg GAE/100 g of DW), followed by cv. Kerman (365.38 mg GAE/100 g of DW). Changes in the antioxidant capacity of pistachio nuts were consistent with changes in flavonoid and TPC. The observed values of RAC with DPPH, FRAP, and β-carotene assays showed that DPPH scavenging ability was stronger, which could be due to specific antioxidant compounds discovered in pistachio nuts. In the present study, TPC in pistachio nuts presented high variability between cultivars under three water regimes. It was observed that treatments T0 and T1 presented high values of bioactive compounds whereas treatment T2 presented lower values. As stated by Ojeda-Amador et al. (2019), the observed variability in phenolic compounds was explained by different factors, such as cultivar, geographical origin, ripening stage, and industrial processing. Our findings were in line with the results of Noguera-Artiaga et al. (2020a), reporting that moderate RDI (T1 treatment) produced nuts with good functional quality (high values of TPC and antioxidant capacity), without affecting their sensory quality.

Table 4. Phenolic compounds in pistachio nuts under RDI.

Traits Mateur Elguetar Kerman Ohadi
Pistachio fresh nuts
Anthocyanins T0 7.72 ± 2a,A 6.63 ± 1a,B 6.38 ± 2a,B 8.25 ± 1a,A
T1 6.78 ± 2a,A 5.98 ± 1a,B 5.82 ± 2a,B 7.51 ± 1a,A
T2 4.85 ± 2b,A 4.38 ± 1b,A 3.40 ± 2b,B 4.33 ± 1b,A
Flavonoids T0 12.18 ± 0.2a,B 10.63 ± 0.1a,B 15.38 ± 0.1a,A 14.25 ± 0.1a,A
T1 13.28 ± 0.2a,A 8.68 ± 0.1a,B 12.82 ± 0.1a,A 13.51 ± 0.1a,A
T2 8.75 ± 0.2b,B 7.38 ± 0.1b,B 9.40 ± 0.1b,A 10.33 ± 0.1b,A
Total phenols T0 410.50 ± 0.1a,A 323.63 ± 0.1a,B 365.38 ± 0.1a,B 334.25 ± 0.2a,B
T1 385.50 ± 0.1a,A 300.20 ± 0.1a,B 305.58 ± 0.1b,B 344.51 ± 0.2a,A
T2 311.50 ± 0.1b,A 207.38 ± 0.1b,C 257.40 ± 0.1c,B 237.33 ± 0.2b,A
RAC T0 121.90 ± 0.5a,B 131.20 ± 0.2a,B 162.43 ± 0.5a,A 153.00 ± 0.2a,A
T1 112.40 ± 0.5a,C 123.08 ± 0.2a,B 142.99 ± 0.5a,A 132.69 ± 0.2a,B
T2 84.31 ± 0.5c,B 92.75 ± 0.2b,A 73.46 ± 0.5b,C 102.47 ± 0.2b,A
FRAP T0 125.00 ± 1.5a,B 123.00 ± 0.5a,B 150.00 ± 1.5a,A 140.00 ± 0.5a,A
T1 110.00 ± 1.0b,C 120.00 ± 2.0a,B 140.00 ± 1.5a,A 143.00 ± 1.0a,A
T2 100.50 ± 0.5b,B 123.00 ± 1.0a,A 115.00 ± 1.0b,A 98.00 ± 2.0b,B
β-carot (%) T0 60.50 ± 2.0ª,A 56.50 ± 1.0ª,A 40.00 ± 2.0ª,A 42.50 ± 2.0b,B
T1 55.0 ± 3.0a,A 52.0 ± 2.0a,A 45.50 ± 2.0a,A 57.10 ± 3.0a,A
T2 40.60 ± 2.0b,B 43.60 ± 3.0b,B 37.20 ± 1.0b,B 52.20 ± 2.0a,A
ANOVA C * * * *
T ** ** ** **
C*T * * * *

Anthocyanin: mg C3Geq kg-1 of DW; flavonoids: mg CE/100 g of DW; total phenols: mg GAE/100 g of DW; RAC: relative antioxidant capacity (μg TE/g of DW). C3Geq: Cyanidin-3-glucoside equivalents; CE: catechin equivalents; GAE: gallic acid equivalence; β-carot: β-carotene bleaching activity; DW: dry weight.

Values are means (n = 3) ± SE. Different superscripted lowercase letters a, b, and c indicate difference (p < 0.05) among the irrigation treatments in the same cultivar. Superscripted uppercase letters A, B, and C indicate differences (p < 0.05) among cultivars (C) in the same treatment (T) (T0: control [100% ETc]; T1: treatment RDI [50% ETc during stage I and stage of nut development and 100% ETc during the stage III]; T2: stressed treatment (50% ETc).

Physicochemical and biochemical parameters of pistachio oil

Physicochemical parameters of pistachio oil

Pistachio oil samples were investigated for acidity, chlorophyll, carotenoid pigments, and specific extinction coefficient (K232, and K270) as shown in Table 5. Physicochemical parameters varied between cultivars whereas water regimes did not show significant differences. Acidity showed a statistically significant difference (p < 0.05) between the studied cultivars. Cv. Ohadi showed the highest value (0.55 g/100 g) of acidity with treatment T2 whereas the lowest value (0.32 g/100 g) was observed in cv. Mateur with treatment T1. The lower values of acidity in oil samples of raw kernels indicated that hydrolytic rancidity had not occurred. Oil acidity observed in the present study was in the range of 0.37–0.62 meq O2/kg of oil, as also reported by Daneshmandi et al. (2014).

Table 5. Physicochemical and biochemical parameters of pistachio oil of the four studied cultivars grown with RDI treatments.

Cultivar Treatment Acidity Chlorophyll Carotenoids K232(1%) K270(1%) Total phenols RAC FRAP β-carot
Mateur T0 0.35 ± 0.1a,B 3.89 ± 0.05a,C 27.38 ± 2.0a,C 1.85 ± 0.14a,B 0.17 ± 0.04a,A 128.26 ± 0.1a,B 48.80 ± 0.5a,B 52.50 ± 1.0a,B 47.20 ± 2.0a,B
T1 0.32 ± 0.2b,B 4.20 ± 0.01a,B 26.59 ± 1.6a,B 1.88 ± 0.25a,B 0.15 ± 0.05a,A 127.21 ± 0.1a,B 42.40 ± 0.5b,A 40.10 ± 0.5b,B 35.70 ± 1.5b,B
T2 0.40 ± 0.1a,B 3.93 ± 0.27a,C 27.27 ± 0.7a,B 1.84 ± 0.11a,B 0.17 ± 0.01a,A 113.79 ± 0.1b,B 30.20 ± 0.5c,A 50.50 ± 1.0a,A 45.30 ± 2.0a,A
Elguetar T0 0.44 ± 0.1a,A 4.91 ± 0.96a,B 31.61 ± 2.1a,B 1.98 ± 0.19a,A 0.14 ± 0.03a,A 109.58 ± 0.1a,C 53.63 ± 0.2a,A 62.20 ± 0.5a,A 57.10 ± 1.5a,A
T1 0.37 ± 0.2a,B 4.71 ± 0.40a,B 34.74 ± 1.4a,A 2.12 ± 0.11a,A 0.15 ± 0.04a,A 113.36 ± 0.1a,B 40.98 ± 0.2b,A 53.50 ± 1.0b,A 48.20 ± 1.0b,A
T2 0.40 ± 0.1a,B 4.63 ± 0.64a,B 32.43 ± 0.3a,A 2.01 ± 0.41a,A 0.14 ± 0.07a,A 101.55 ± 0.1b,B 27.38 ± 0.2c,B 45.50 ± 0.5c,B 40.30 ± 1.5c,B
Ohadi T0 0.49 ± 0.1a,A 7.35 ± 0.05b,A 38.04 ± 2.0a,A 2.17 ± 0.10a,A 0.18 ± 0.04a,A 138.85 ± 0.2a,A 47.25 ± 0.2a,B 45.55 ± 0.5a,C 40.25 ± 1.5a,C
T1 0.42 ± 0.1b,A 8.11 ± 0.05a,A 38.66 ± 2.0a,A 2.31 ± 0.11a,A 0.19 ± 0.01a,A 137.25 ± 0.2a,A 37.51 ± 0.2b,B 47.20 ± 1.5a,B 42.70 ± 2.5a,B
T2 0.55 ± 0.1a,A 7.80 ± 0.95a,A 36.37 ± 2.0b,A 2.05 ± 0.10b,A 0.17 ± 0.01a,A 125.41 ± 0.2b,A 27.33 ± 0.2c,B 47.15 ± 2.0a,B 44.55 ± 1.0a,A
Kerman T0 0.43 ± 0.1b,A 5.07 ± 0.31a,B 29.28 ± 4.2a,C 1.67 ± 0.06b,C 0.15 ± 0.03b,A 73.25 ± 0.1b,C 40.80 ± 0.5a,C 50.20 ± 1.5a,C 45.50 ± 2.5a,C
T1 0.43 ± 0.1b,A 5.35 ± 0.09a,B 29.21 ± 6.4a,B 1.86 ± 0.05a,B 0.18 ± 0.03a,A 76.67 ± 0.1a,C 32.82 ± 0.5b,C 30.10 ± 1.0b,C 25.50 ± 2.0b,C
T2 0.54 ± 0.1a,A 5.34 ± 0.42a,B 29.39 ± 1.2a,B 1.71 ± 0.04a,B 0.16 ± 0.04a,A 68.29 ± 0.1c,C 22.40 ± 0.5c,C 32.20 ± 0.5b,C 27.50 ± 1.5b,C
ANOVA C * * * * NS * * * *
T * * * * NS * * * *
C*T * NS NS NS NS ** ** ** **

Acidity: g 100 g-1; chlorophyll: mg kg-1; carotenoids: mg kg-1; K232 = absorbance at a wavelength of 232 nm; K270 = absorbance at a wavelength of 270 nm; total phenols: mg kg-1; RAC: relative antioxidant capacity (μg TEg-1 of DW). T0: control (100% ETc); T1: regulated deficit irrigation (RDI; 50% ETc during stage I and stage of nut development and 100% ETc during stage III); T2: stressed treatments (50% ETc).

Values are means (n = 3) ± SE. Different superscripted lowercase letters a, b, and c indicate difference (p < 0.05) among three irrigation treatments (T0, T1, and T2) in the same cultivar. Different superscripted uppercase letters A, B, and C indicate differences (p < 0.05) among cultivars in the same treatment.

Arena et al. (2007) found 6.8 meq O2/kg of oil as peroxide number in Iranian pistachio oil. Yahyavi et al (2020) reported that the peroxide number was the main indicator of fat oxidation, measuring the concentration of hydroperoxide formed during lipid oxidation. The specific extinction index is often used to evaluate the presence of primary (K232) or secondary (K270) oxidation products. The K232 values in pistachio oil were higher in cv. Ohadi (2.17, 2.31, and 2.05 for treatments T0, T1, and T2, respectively) followed by cv. Elguetar. Interestingly, no significant variation of RI, even at 270 nm, was observed in pistachio oil of the studied cultivars. RI of pistachio oil samples was the same between cultivars (1.47) and years of study. These results were consistent with the results of the previous studies, reporting that the RI of pistachio oil was around 1.4 for different varieties and regions without any significant changes (Yahyavi et al., 2020; Yildiz et al., 1998). Results further showed that cv. Ohadi showed the most considerable content of chlorophyll for three irrigation regimes (7.35, 8.11, and 7.8 mg/kg for treatments T0, T1, and T2, respectively). However, carotenoids content showed a significant difference (p < 0.05) between cultivars. Hence, carotenoid dominated in cv. Ohadi (38.04, 38.66, and 36.37 mg/kg for treatments T0, T1, and T2, respectively), followed by cv. Elguetar. Analysis revealed that the oil extracted from cv. Mateur had the lowest content of carotenoids (25.38 mg/kg) for treatment T0. Treatment T0 showed lower values of carotenoids, compared to treatments T1 and T2. Bellomo and Fallico (2007) reported that the content of pigments in pistachio oils was in the range of 18–52 mg/kg of DW. These values were linked to genotype, degree of ripeness, environmental conditions, and geographical origin (Giuffrida et al., 2006).

Biochemical parameters of pistachio oil

The TPC of the extracted pistachio oil in control and treatment T1 was the same, showing a statistically significant difference (p < 0.05) with the treatment T2 (Table 5). Among cultivars studied, TPC of pistachio oil samples showed statistically significant differences (p < 0.05). Cv. Ohadi had the highest values of TPC, followed by cv. Mateur and Elguetar, while cv. Kerman presented the lowest values of TPC for three irrigation treatments. Irrigation treatments significantly affected the TPC, with treatment T2 presenting lower values for the four studied cultivars. These results were in line with the study done by Miraliakbari and Shahidi (2008), showing a TPC of 158 mg/kg oil for commercial pistachio. Irrigation treatments affected significantly the TPC, with treatment T2 presenting the lowest values in the four studied cultivars.

The RAC values conducted with DPPH assay showed values of DPPH ranging from 22.40 µg TE/g to 53.63 µg TE/g of oil. Pistachio oil from treatment T2 always presented lower values of RAC, compared to treatment T0 and RDI (treatment T1). Extracted oil from cv. Kerman showed lower values for AC and presented statistically significant difference (p < 0.05) compared to cv. Mateur, Ohadi, and Elguetar. The AC values were consistent within the range of 20.7–87.4 µg TE/g of oil as reported in a previous paper on fatty acid composition, antioxidant, and antibacterial activities of Pistacia fruit oils (Mezni et al., 2020).

Correlations between antioxidant compounds

Pearson’s correlation between antioxidants showed a strong positive association between total phenols and DPPH (r = 0.45), flavonoids and anthocyanin (r = 0.56), flavonoids and FRAP (r = 0.52), and flavonoids and β-carot (r = 0.40) (Table 6). A low positive correlation was observed between anthocyanin and β-carot (r = 0.32). Negative correlations were observed between total phenols and flavonoids (r = -0.50), total phenols and anthocyanin (r = -0.62), total phenols and FRAP (r = -0.68), and anthocyanin and β-carot (r = -0.70). Moreover, a positive relationship (r = 0.45) that manifested between total phenols and DPPH implied the contribution of phenols in DPPH capacity. However, total phenols showed a negative correlation with FRAP and β-carot. Meanwhile, flavonoids and anthocyanin had a positive correlation with FRAP and β-carot but a negative association with DPPH. These demonstrated their contributions to radical scavenging in pistachio nuts, but they were not key components of DPPH activity.

Table 6. Correlation between antioxidants and antioxidant activity in pistachio nuts.

TP Flav Anth FRAP DPPH β-carot
TP 1 –0.50** –0.62** –0.68** 0.45** –0.70**
Flav 1 0.56** 0.52** –0.32* 0.40*
Anth 1 0.60** –0.42** 0.32**
FRAP 1 –0.10NS 0.60**
DPPH 1 –0.37**
β-carot 1

*, **, and *** indicate significance at p < 0.05, 0.01, and 0.001, respectively.

NS = not significant; TP: total phenols; Flav: flavonoids; Anth: anthocyanin; FRAP: ferric-reducing antioxidant power; DPPH: 1,1-diphenyl-2-picrylhydrazyl capacity; β-carot: β-carotene bleaching activity assay.

Content of volatile compounds in nuts

The analysis of volatile compounds in raw pistachio nuts identified 76 volatiles belonging to the chemical classes of acids, aldehydes, alcohols, terpenes, ketones, esters, aromatics, and nitrogen compounds as shown in Table 7. Water regime affected the volatile content of the studied cultivars, showing high values in treatment T2 whereas treatments T0 and T1 presented similar volatile compounds content. The most abundant compounds were terpenes, such as α-pinene, terpinolene, and limonene, followed by 1-methyl-pyrrole. Terpenes and 1-methyl-pyrrole (nutty and sweet) constituted 80% of volatile compounds. The results revealed statistically significant differences (p < 0.05) in the contents of volatile compounds of the studied cultivars under three water regimes. The amount of terpenes and 1-methyl-pyrrole in raw pistachio nuts was higher with T2 stressed treatment in all studied cultivars. In the same manner, aliphatic alcohols, aldehydes, and 1-methyl-pyrrole also increased with decrease in water regime. Hence, the amount of 1-methyl-pyrrole increased by about 50% in cv. Mateur and Ohadi with stressed treatment T2. Alcohols were the second most represented class consisting mainly of 1-hexanol, 1-nonanol, and 1-dodecanol. Among the aldehydes, nonanal (nonanaldehyde) had the highest content, especially in cv. Ohadi and Elguetar.

Table 7. Amount* of volatile aroma compounds for classes of substances in raw pistachio samples of the four studied pistachio cultivars subjected to different irrigation treatments.

Compounds LRI Mateur Kerman Ohadi Elguetar
VF-Vax SLB-5 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2
Acids
  Acetic 1,448 596 195b 201b 176a 273b 284b 142a 174a 172a 314b 157a 143a 296b
  Isobutyric 1,566 742 54b 60b 0a 10a 15a 18a 103b 111b 88a 46b 50b 35a
  Pentanoic 1,740 894 101b 105b 36a 40a 38a 43a 161b 180b 70a 35a 36a 53b
  Hexanoic 1,849 983 200a 206a 225b 372b 315a 325a 342a 349a 387a 361a 386a 526b
  2-Ethyl-hexanoic 1,952 1,123 32a 33a 38a 75b 79b 25a 53a 52a 47a 20a 29a 48b
  Octanoic 2,062 1,180 173b 159b 84a 79a 96b 77a 150a 172a 163a 214b 244b 136a
  Nonanoic 2,149 1,280 119a 125a 208b 162b 120a 135a 389b 355b 319a 172a 170a 230b
  All 874b 889b 767a 1011c 947b 765a 1,372a 1,391a 1,388a 1,005a 1,058a 1,324b
Aldehydes
  2-Methyl-butanal 915 646 55a 53a 78b 71a 71a 96b 33a 25a 87b 23a 29a 48b
  3-Methyl-butanal 919 652 20a 17a 44b 28a 22a 39b 12a 19a 30b 13a 19a 38b
  Hexanal 1,076 810 850a 871a 1218b 356a 359a 579b 165a 166a 374b 504a 578a 842b
  Heptanal 1,175 912 410a 428a 531b 180a 235a 295b 121a 133a 289b 146a 143a 267b
  Octanal 1,279 1,006 120a 132a 245b 30a 26a 56b 60a 58a 254b 235a 241a 320b
  (Z)-2-Heptenal 1,316 964 129a 144a 172b 29a 35a 50b 95a 93a 184b 79a 84a 188b
  Nonanal 1,377 1,107 410a 432a 552b 495a 545a 968b 1,732a 1,681a 3,819b 2,491a 2,556b 3,344c
  (E)-2-Octenal 1,419 1,057 33a 34a 40a 80a 79a 203b 63a 66a 124b 24a 27a 31a
  Decanal 1,491 1,209 168a 177a 264b 175a 157a 246b 216a 230a 351b 128a 155a 258b
  Benzaldehyde 1,520 953 166a 167a 189b 133a 131a 238b 132a 133a 281b 75a 84a 186b
  (E)-2-Nonenal 1,530 1,161 144a 136a 240b 160a 122a 273b 180a 226a 337b 145a 104a 270b
  1-Methyl-pyrrole-2-carboxaldehyde 1,621 993 39a 41a 84b 27a 21a 47b 26a 21a 102b 26a 24a 72b
  All 2,544a 2,632a 3,657b 1,764a 1,803a 3,090b 2,835a 2,851a 6,232b 3,889a 4,044b 5,864c
Alcohols
  2-Methyl-1-butanol 1,201 730 289a 275a 394b 97a 107a 209b 88a 99a 150b 99a 100a 143b
  1-Pentanol 1,240 768 92a 90a 254b 168a 199b 618c 603a 622a 859b 323a 360a 786b
  Heptan-2-ol 1,307 900 125a 129a 266b 80a 76a 120b 112a 116a 380b 81a 111a 144b
  Hexanol 1,340 871 364a 344a 750b 1,574a 1,523a 2,683b 2,202a 2,209a 2,861b 3,064a 3,066a 4,025b
  2-Butoxy-ethanol 1,393 910 160a 175a 219b 330a 344a 578b 308a 302a 411b 253a 279a 324b
  2-Octanol 1,406 997 77a 89a 132b 32a 47a 68b 53a 86a 124b 58a 55a 137b
  1-Octen-3-ol 1,437 985 240a 220a 331b 177a 156a 321b 174a 163a 240b 223a 236a 290b
  1-Heptanol 1,443 972 270b 201a 633c 275a 284a 511b 350a 363a 383a 337a 339a 778b
  6-Methyl-hept-5-en-2-ol 1,451 994 87a 90a 161b 105a 120a 277b 105a 101a 154b 79a 106a 183b
  2-Ethyl-1-hexanol 1,477 1,038 271a 293a 335b 449a 474a 597b 510a 501a 584b 340a 376a 476b
  Nonan-2-ol 1,507 1,088 53a 41a 90b 45a 53a 87b 60a 62a 118b 52a 67a 139b
  1-Octanol 1,548 1,075 328a 377a 643b 1,311a 1,297a 2,773b 631a 637a 950b 851a 868a 938b
  1-Nonanol 1,653 1,172 387a 417a 532b 727a 785a 899b 955a 958a 1,112b 1,039a 1,047a 1,494b
  (Z)-3-Nonen-1-ol 1,680 1,160 43a 40a 124b 56a 53a 151b 46a 42a 92b 46a 56a 79a
  1-Decanol 1,760 1,267 102a 99a 216b 72a 85a 167b 81a 87a 101a 109a 138a 222b
  Benzylalchohol 1,879 1,029 176a 173a 240b 175a 173a 241b 216a 213a 245b 361a 343a 480b
  Phenylethylalchohol 1,913 1,112 80a 92a 190b 165a 135a 294b 132a 184a 257b 313a 317a 397b
  1-Dodecanol 1,967 1,475 317a 378a 991b 205a 184a 292b 148a 114a 765b 112a 139a 472b
  All 3,461a 3,523a 6,501b 6,043a 6,095a 10,886b 6,774a 6,859b 9,786c 7,740a 8,003b 11,507c
Terpenes
  Tricyclene 1,005 922 129a 119a 246b 76a 78a 180b 112a 102a 200b 131a 140a 268b
  α-Pinene 1,019 940 1,6103b 15,895a 17,433c 11,018a 12,897b 15,450c 13,458a 13,357a 16,501b 15,071a 15,602b 16,309c
  α-Thujene 1,023 932 76a 83a 96a 222a 201a 390b 224a 217a 402b 81a 100a 123a
  α-Fenchene 1,052 953 53a 43a 79a 59a 54a 70a 38a 37a 47a 59a 61a 74a
  Camphene 1,058 955 473a 502a 654b 393a 362a 1034b 500a 529a 661b 522b 474a 637c
  β-Pinene 1,094 980 808a 807a 934b 399a 530b 1483c 1780a 1774a 1851b 663a 639a 750b
  Sabinene 1,107 978 40a 38a 57a 138a 134a 202b 91a 91a 111a 42a 30a 61a
  2-Carene 1,119 1006 80a 82a 113a 108a 114a 137b 87a 104a 245b 46a 42a 149b
  3-Carene 1,128 1,012 445a 456a 483a 215a 234a 340b 514a 487a 670b 138a 173b 571c
  Myrcene 1,138 991 809a 806a 1420b 818a 849a 2,575b 1,113a 1,114a 1,325b 1,954a 2,232b 3,817c
  α-Phellandrene 1,141 1,005 106a 117a 320b 217a 255a 278a 192a 183a 282b 138a 146a 274b
  α-Terpinene 1,153 1,018 158a 144a 250b 212a 192a 600b 250a 288a 356b 284a 258a 860b
  Limonene 1,183 1,032 2,215a 2,243a 4,088b 12,618a 13,499b 16,691c 11,528a 11,842b 17,707c 10,768a 10,943b 12,120c
  β-Phellandrene 1,194 1,030 210a 261a 356b 369a 318a 553b 423a 429a 385b 132a 187a 328b
  γ-Terpinene 1,231 1,064 335a 327a 456b 1351b 1292a 1516c 632a 640a 1211b 742a 754a 938b
  β-Ocimene 1,236 1,050 50a 43a 73a 208a 183a 326b 49a 37a 82b 489a 532a 937b
  p-Cymene 1,246 1,022 1,778a 1,786a 1,813b 2,365a 2,500b 3,202c 1,448a 1,997b 3,029c 2,206a 2,292b 2,957c
  o-Cymene 1,250 1,021 47a 50a 105b 344a 360a 429b 207a 209a 316b 15a 37a 79b
  Terpinolene 1256 1088 9421a 9394a 10058b 2119a 2159a 5743b 2612a 2789b 3664c 6958b 6875a 7794c
  p-Mentha-1,5,8-triene 1,410 1,113 180a 197a 330b 61a 52a 80a 69a 76a 80a 101a 128a 282b
  p-Cymenene 1,423 1,091 1,078a 1,016a 1,498b 512a 503a 614b 599a 580a 966b 1,404a 1,438a 2,669b
  m-Cymenene 1,431 1,085 68a 79a 139b 352a 314a 402b 243a 255a 412b 152a 134a 233b
  Camphor 1,509 1,143 78a 95a 154b 137a 124a 255b 99a 118a 271b 128a 127a 310b
  Linalool 1,536 1,098 117a 111a 285b 242a 283a 363b 129a 109a 227b 173a 158a 314b
  α-Terpineol 1,694 1,191 38a 30a 89b 105a 109a 242b 38a 37a 62b 26a 39a 86b
  m-Cymen-8-ol 1,850 1,185 179a 187a 389b 161a 168a 208b 162a 187a 206b 294a 287a 423b
  Nerylacetone 1,855 1,435 90a 87a 219b 23a 29a 50b 19a 25a 53b 80a 62a 142b
  Eucalyptol 1,190 1,032 44a 35a 75b 870a 872a 902b 113a 106a 143b 38a 53a 114b
  Bornylacetate 1,575 1,280 20a 25a 58b 38a 37a 51b 35a 32a 48a 18a 16a 112b
  All 35,228a 35,058a 42,270b 35,750a 38,702b 54,366c 36,764a 37,751b 51,513c 42,853a 43,959b 53,731c
Ketones
  6-Methyl-5-hepten-2-one 1,326 986 113a 156b 220c 208a 235a 391b 136a 151a 321b 320a 305a 691b
  Oct-3-en-2-one 1,399 1,040 34a 46a 176b 89a 83a 177b 55a 60a 134b 119a 141a 235a
  Acetophenone 1,651 1,068 43a 37a 131b 32a 54a 137b 41a 62a 152b 48a 39a 138b
  All 190a 239a 527b 329a 372a 705b 232a 273a 607b 487a 485a 1,064b
Others
  Toluene 1,038 761 83a 94a 79a 148b 100a 84a 183a 163a 155a 145b 99a 121b
  1-Methyl-pyrrole 1,133 750 3,917a 3,952a 6,925b 5,462a 5,612b 7,415c 2,648a 2,700b 5,901c 2,790a 2,863a 5,374b
  Styrene 1,242 889 35a 28a 25a 22a 20a 55b 36a 18a 32a 41a 31a 49a
  Octylacetate 1,465 1,213 15a 24a 48b 105b 105b 67a 44a 40a 55a 36a 35a 71b
  Benzothiazole 1,956 1,224 351a 347a 428b 279a 270a 432b 361a 388a 410b 340a 355a 417b
  Phenol 2,011 992 212a 204a 354b 270a 263a 320b 244a 276a 348b 250a 230a 355b
  γ-Nonalactone 2,032 1,344 36a 20a 124b 13a 20a 52b 35a 42a 143b 35a 45a 85b
  All 4,649c 4,677c 8,031a 6,301b 6,390b 8,425a 3,551c 3,627c 7,044b 3,637c 3,658c 64,72b

Peak area, arbitrary scale; T0: control; T1: regulated deficit irrigation (RDI); T2: stressed; different lowercase superscripted letters in the same row indicate difference (p < 0.05) among three irrigation treatments (T0, T1, and T2) and cultivars by Scheffe´s test.

Seventy volatiles were identified in pistacho nuts after the roasting process, including acids, aldehydes, alcohols, terpenes, ketones, esters, aromatic compounds, pyridine, pyrazines, pyrimidines, and furan derivatives (Table 8). The predominant volatile compounds were α-pinene and limonene, which are terpenes. Terpenes constituted the primary class of substances, comprising 50% of all volatile compounds, followed by aldehydes and nitrogenous compounds. The roasted pistachio showed an evident increase in pyridine, pyrazines, pyrimidines, furan derivatives, and aldehydes arising from Maillard reaction during roasting (Table 8).

Table 8. Amount* of volatile compounds and classes of substances in roasted pistachio samples of the four studied pistachio cultivars subjected to different irrigation treatments.

Compounds LRI Mateur Kerman Ohadi Elguetar
VF-Vax SLB-5 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2
Acids
  Acetic 1,448 596 584a 591a 649b 514b 548b 437a 261a 395b 372b 220a 252a 339b
  Pentanoic 1,740 894 55a 50a 55a 49a 57a 71b 41a 43a 48a 73a 89a 135b
  Hexanoic 1,849 983 755b 784b 703a 328b 273a 305b 547a 564a 559a 1,309a 1,399b 1,322a
  Heptanoic 1,956 1,083 336a 363b 316a 219a 210a 238a 204a 235b 238b 442a 410a 580b
  Octanoic 2,062 1,180 286a 269a 332b 89a 76a 85a 117a 126a 144b 378a 357a 395b
  Nonanoic 2,149 1,280 351b 327a 320a 119a 118a 165b 217a 249b 213a 221a 220a 225a
  All 2,367a 2,384a 2,375a 1,318b 1,282a 1,301b 1,387a 1,612c 1,574b 2,643a 2,727b 2,996c
Aldehydes
  2-Methyl-butanal 915 646 2,148a 2,604b 2,847c 1,674a 1,975b 3,412c 1,858a 1,856a 5,229b 4,733a 4,733a 6,105b
  3-Methyl-butanal 918 652 972a 977a 1083b 684a 688a 890b 449a 495a 631b 155a 180a 348b
  Pentanal 919 715 307a 316a 445b 248a 273a 478b 170a 147a 509b 129a 126a 345b
  Hexanal 1,076 810 1,658a 1,617a 2,404b 1,073a 1,016a 2,436b 1,388a 1,381a 1,783b 1,300a 1,356a 2,675b
  Heptanal 1,175 912 378a 373a 423b 113a 92a 501b 746a 791a 948b 584a 589a 813b
  Octanal 1,279 1,006 748a 725a 1514b 742a 699a 822b 919a 918a 2,705b 1,444a 1,440a 2,189b
  Nonanal 1,377 1,107 5,250a 5,166a 8,844b 2,580a 2,573a 4,084b 2,81a 2,70a 398b 56a 64a 780b
  (E)-2-Octenal 1,419 1,057 19a 65b 91c 32a 24a 76b 55a 91a 276b 272a 261a 315b
  Decanal 1,491 1,209 45a 56a 98b 12a 18a 54b 154a 172a 360b 60a 76a 122b
  Benzaldehyde 1,520 953 467a 418a 611b 609a 655a 758b 890a 848a 1,082b 769a 761a 1,494b
  (E)-2-Nonenal 1,530 1,161 292a 350b 540c 11a 16a 23b 69a 70a 199b 39a 44a 77b
  1-Methy-pyrrole-2-carboxaldehyde 1,621 993 154a 146a 385b 112a 122a 295b 129a 139a 424b 322a 307a 465b
  Benzeneacetaldehyde 1,644 1,043 74a 78a 199b 156a 167a 300b 232a 231a 430b 54a 67a 154b
  Pyrrole-2-carboxaldehyde 2,028 1,015 45a 56a 123b 51a 75b 90c 59a 82a 134b 78a 99a 236b
  All 12,557a 12,947a 19,607b 8,097a 8,393a 14,219b 7,399a 7,491a 15,108b 9,995a 10,103b 16,118c
Alcohols
  2-Methyl-1-butanol 1,201 730 178a 201b 369c 312a 325a 426b 163a 165a 542b 160a 187a 255b
  Hexanol 1,340 871 1,435a 1,433a 2,395b 1,066a 1,087a 1,941b 1,739a 1,762a 2,380b 963a 1,116a 2,451b
  2-Octanol 1,406 997 71a 82a 124b 61a 40a 120b 103a 110a 261b 398a 421a 564b
  1-Heptanol 1,443 972 487a 481a 710b 251a 221a 599b 341a 447a 644b 165a 184a 295b
  2-Ethyl-1-hexanol 1,478 1,038 165a 219b 375c 330a 302a 473b 257a 276a 894b 357a 365a 723b
  1-Octanol 1,548 1,548 1,114a 1,180a 1,575b 1,156a 1,178a 2,106b 1,073a 1,072a 2,111b 87a 85a 180b
  1-Nonanol 1,653 1,653 539a 615b 824c 534a 554a 680b 599a 601a 791b 419a 467a 606b
  Benzylalchohol 1,879 1,029 56a 59a 143b 179a 144a 214b 176a 168a 602b 420a 452a 676b
  Phenylethylalchohol 1,913 1,112 167a 162a 209b 300a 335a 410b 516a 547a 702b 170a 179a 739b
  1-Dodecanol 1,967 1,475 1,193a 1,200b 1,738c 70a 132b 274c 94a 90a 163b 61a 67a 99b
  Pentadecanol 2,151 1,778 352a 298a 451b 69a 64a 80b 42a 41a 100b 29a 32a 75b
  All 5,757a 5,930a 8,913b 4,328a 4,382a 7,323c 5,103a 5,279a 9,190b 3,229a 3,582a 6,663b
Terpenes
  Tricyclene 1,005 922 127a 132a 303b 124a 100a 208b 154a 161a 268b 105a 108a 129b
  α-Pinene 1,019 940 14,739a 1,5114b 16,556c 10,193a 10,997b 13,215c 14,984a 15,700b 16,259c 13,722a 14,159b 16,063c
  α-Thujene 1,023 932 111a 103a 228b 198a 192a 303b 161a 167a 346b 309a 370a 910b
  Camphene 1,058 955 669a 613a 768b 851a 857a 1043b 693a 695a 757b 659a 652a 789b
  β-Pinene 1,094 980 859a 870a 1020b 1015a 1020a 1240b 980a 1074b 2079c 491a 538a 679b
  Sabinene 1,107 978 24a 30a 44a 35a 55a 105b 130a 123a 168b 109a 118a 236b
  Myrcene 1,138 991 1,296a 1,323a 1,582b 1,077a 1,080a 1,406b 1,281a 1,465b 3,278c 2,328a 2,883b 4,570c
  α-Terpinene 1,153 1,018 291a 297a 378b 424a 444a 792b 251a 283a 366b 1,729a 1,770a 2,917b
  Limonene 1,183 1,032 6,313a 6,867b 9,348c 9,266a 9,366b 10,613c 10,855a 10,852a 15,004b 1,4888a 15,821b 17,002c
  β-Phellandrene 1,194 1,030 201a 170a 309b 388a 420a 540b 381a 417a 638b 359a 439b 664c
  γ-Terpinene 1,231 1,064 612a 669a 909b 613a 627a 836b 846a 870a 1123b 626a 666a 860b
  p-Cymene 1,260 1,022 1,610a 1,632a 2,541b 2,455a 2,480a 2,728b 3,158b 2,907a 7,239c 9,618a 9,784b 11,656c
  Terpinolene 1,273 1,088 5,063a 5,101b 6,664c 1,365a 2,155b 3,659c 2,406a 2,420a 3,641b 1,709a 1,720a 3,275b
  p-Mentha-1,5,8-triene 1,410 1,113 128a 169a 212b 33a 35a 89b 76a 70a 138b 105a 148a 229b
  p-Cymenene 1,423 1,019 185a 170a 282b 204a 201a 291b 366a 336a 432b 319a 320a 665b
  Linalool 1,537 1,191 71a 80a 142b 129a 191a 295b 93a 131a 732b 222a 227a 412b
  Bornylacetate 1,575 1,280 34a 39a 80b 59a 67a 132b 37a 27a 91b 52a 60a 179b
  m-Cymen-8-ol 1,850 1,185 521a 521a 722b 273a 276a 400b 357a 443b 553c 447a 477a 770b
  All 32,854a 33,900b 42,088c 28,702a 30,563b 37,895c 37,259a 38,141b 53,112c 47,797a 50,260b 62,005c
Nitrogenous
  2,6-Diethyl-pyrazine 1,426 1,093 87a 90a 199b 78a 95a 132b 82a 107a 261b 32a 36a 68b
  3,5-Diethyl-2-methyl-pyrazine 1,486 1,166 543a 571a 763b 430a 441a 540b 162a 230b 348c 45a 47a 173b
  (E)-2-Methyl-5-(1-propenyl)-pyrazine 1,712 1,133 81a 82a 127b 58a 62a 83b 103a 144a 258b 124a 129a 332b
  2-Ethyl-5-methyl-pyrazine 1,378 998 359a 360a 514b 202a 259a 374b 335a 354a 615b 283a 311a 536b
  Trimethyl-pyrazine 1,398 1005 393a 411a 618b 244a 317b 496c 444a 467a 687b 760a 769a 913b
  2,5-Dimethyl-pyrazine 1,318 927 1,369a 1,395a 1,662b 1,060a 1,130b 1,525c 1,099a 1,339b 2,741c 1,169a 1,180a 2,648b
  4,6-Dimethyl-pyrimidine 1,323 928 71a 80a 179b 45a 57a 87b 162a 175a 471b 149a 197a 424b
  2-Ethyl-3,5-dimethyl-pyrazine 1,437 1,082 1,542a 1,557a 2,011b 1,067a 1,072a 1,662b 1,901a 1,966a 2,725b 4,987a 4,990a 6,164b
  N-acetyl-4(H)-pyridine 1,721 1,038 184a 185a 270b 84a 102a 137b 156a 217b 282c 101a 120a 206b
  All 4,629a 4,731b 6,343c 3,268a 3,535b 5,036c 4,444a 4,999b 8,388c 7,650a 7,779b 11,464c
Furans
  2-Pentyl-furan 1,220 992 56a 61a 78a 29a 30a 82b 75a 77a 183b 66a 69a 166b
  Furfural 1,460 836 628a 669a 890b 479a 515b 742c 600a 614a 800b 89a 94a 145b
  5-Methyl-furfural 1,572 964 73a 75a 86b 39a 49a 154b 55a 71a 684b 533a 537a 757b
  2-Furanmethanol 1,659 864 90a 91a 200b 120a 126a 244b 59a 79a 111b 58a 76a 189b
  All 847a 896a 1254b 667a 720b 1222c 789a 841b 1778c 746a 776a 1257b
Ketones
  2,3-Pentanedione 1,055 702 123a 131a 166b 103a 135a 324b 139a 142a 248b 113a 148a 194b
  2-Heptanone 1,174 889 538a 552a 700b 217a 266a 455b 409a 420a 647b 237a 264a 338b
  2-Octanone 1,276 986 803a 816a 1077b 580a 589a 830b 1037a 1041a 1934b 395a 433a 780b
  2-Nonanone 1,380 1,093 99a 120a 184b 64a 68a 112b 78a 98a 187b 70a 78a 135b
  Oct-3-en-2-one 1,401 1,040 318a 319a 240b 137a 139a 272b 116a 155a 289b 238a 241a 309b
  Acetophenone 1,650 1,068 34a 43a 97b 86a 94a 180b 68a 78a 92b 12a 24a 113b
  All 1,915a 1,981a 2,464b 1,187a 1,291b 2,173c 1,847a 1,934b 3,397c 1,065a 1,188b 1,869c
Pyrroles
  1-methyl-pyrrole 1,133 750 3,098a 3,173b 5,064c 8,174a 8,260b 10,632c 4,067a 4,099a 4,725b 4,187a 4,190a 5,164b
Others
  Phenol 2,011 992 234a 268a 432b 15a 35a 86b 249a 267a 374b 143a 154a 327b

*Peak area, arbitrary scale; T0: control; T1: regulated deficit irrigation (RDI); T2: stressed; different lowercase superscripted letters in the same row indicate difference (p < 0.05) among three irrigation treatments (T0, T1, and T2) and different cultivars by Scheffe’s test. Each compound was identified using mass spectral data, NIST’ 20 and FFNSC 3.0 database, linear retention indices (LRI) according to the Van Den Dool and Kratz equation, calculated on VF-Wax 60 m and SLB-5ms 30-m capillary columns.

Irrigation treatments have similar effects on the content of volatile compounds of raw and roasted pistachio nuts. Results showed that terpenes were the most abundant compounds. Kendirci and Onoğur (2011), studying raw pistachio nuts of different cultivars in Turkey, observed that terpenes and mainly α-pinene (pine-like, resinous) were the major volatile compounds contributing to flavor. These authors suggested that terpenes and 1-methyl-pyrrole were the key odorants found in the highest amount in all cultivars grown under the T2 stressed treatment. Key aroma compounds, such as terpenes, aldehydes, and nitrogenous compounds, were improved in raw and roasted nuts grown under the T2 irrigation treatment. Galindo et al. (2018) reported that severe RDI during stage II increased the contents of aldehydes and reduced those of pyrazines and terpenes. These findings were in accordance with the results shown by Şahan and Bozkurt (2020), reporting that flavoring compounds were higher in rain-fed pistachios than irrigated trees and the concentration of terpenes, the most abundant volatile compounds in dried pistachio nuts, decreased with irrigation. Increase in pyridines, pyrazines, pyrimidines, and furan derivatives as well as aldehydes in roasted pistachio was evident. This behavior is related to the roasting process, as these volatiles arise from Maillard reactions as well as from the Strecker degradation of α-amino acids, producing aldehydes and α-aminoketones, as reported by Rodríguez-Bencomo et al. (2015).

Composition of fatty acids

In the present study, the RDI irrigation treatments did not affect the fatty acid profile, and the fatty acid composition didn’t show a consistent behavior with irrigation treatments (Table 9). Moreover, Noguera-Artiaga et al. (2020b) showed that pistachios obtained under moderate RDI (treatment T1) had the highest content of oleic acid and the lowest content of α-linolenic, compared to those of control (T0) and treatment T2. In the same manner, Carbonell-Barrachina et al. (2015) reported that moderate RDI increased the content of linoleic acid. Moreover, 50% ETc water regime (treatment T2) contributed to higher fatty acid content for all cultivars in both years, compared to control (100% ETc) and RDI (T1) treatments. It was clear from the results of this investigation that the fatty acid content appeared to be insensitive to water deficit. This finding confirmed the results of previous investigations under deficit irrigation, showing that deficit irrigation allowed the maintenance of higher fatty acids, compared to full irrigation (Ahumada-Orellana et al., 2018; Motilva et al., 2000). This contrasting behavior could be attributed to the higher influence of varietal factors and climatic conditions on the composition of fatty acids than to water status (Fernandes-Silva et al., 2021).

Table 9. Fatty acids profile of four pistachio nuts grown under RDI treatments.

Cultivar Trt C16:0 C16:1 C17:0 C17:1 C18:0 C18:1 C18:2 C18:3 C20:0 C20:1
  Mateur T0 9.25±0.17aA 0.55±0.01aA 0.02±0.0aA 0.05±0.01aA 1.45±0.04aA 68.23±1.03aA 19.88±1.22aA 0.24±0.01aA 0.07±0.01aA 0.27±0.04aA
   T1 9.48±0.16aA 0.61±0.06aA 0.02±0.0aA 0.04±0.01aA 1.47±0.12aA 68.13±1.29aA 19.70±1.56aA 0.24±0.01aA 0.07±0.01aA 0.26±0.04aA
   T2 9.42±0.31Aa 0.62±0.03aA 0.02±0.0aA 0.04±0.01aA 1.45±0.04aA 68.3 ±0.87aA 19.53±1.24aA 0.24±0.02aA 0.07±0.01aA 0.29±0.02aA
  Elguetar T0 8.47±0.53aB 0.68±0.14aA 0.02±0.0aA 0.05±0.01aA 1.52±0.01aA 68.7 ±0.66aA 19.84±0.01aA 0.30±0.08aA 0.08±0.01aA 0.32±0.06aA
   T1 8.85±0.91aB 0.74±0.09aA 0.02±0.0aA 0.05±0.01aA 1.40±0.02aA 68.7 ±0.89aA 19.63±0.01aA 0.29±0.01aA 0.07±0.01aA 0.21±0.08aA
   T2 8.86±0.69aB 0.71±0.19aA 0.02±0.0aA 0.05±0.01aA 1.51±0.16aA 68.7 ±0.73aA 19.49±0.14aA 0.3±0.02aA 0.06±0.03aA 0.24±0.13aA
  Ohadi T0 9.92±0.15aA 0.81±0.01aA 0.02±0.0aA 0.04±0.01aA 0.95±0.04aB 59.0 ±1.00aB 28.62±1.20aB 0.34±0.00aA 0.05±0.00aA 0.22±0.01aA
   T1 10.13±0.15aA 0.97±0.01aA 0.02±0.0aA 0.05±0.01aA 0.8±0.01aB 58.7 ±1.00aB 28.75±1.02aB 0.28±0.01aA 0.05±0.01aA 0.20±0.01aA
   T2 9.67±0.75aA 0.72±0.18aA 0.02±0.0aA 0.05±0.01aA 0.93±0.06aB 59.4 ±0.37aB 28.52±0.41aB 0.31±0.01aA 0.07±0.01aA 0.27±0.04aA
  Kerman T0 9.35±0.12aA 0.68±0.06aA 0.02±0.0aA 0.05±0.01aA 1.44±0.11aA 68.7 ±0.05aA 19.88±0.22aA 0.26±0.01aA 0.06±0.01aA 0.27±0.01aA
   T1 9.72±0.55aA 0.69±0.01aA 0.02±0.0aA 0.05±0.01aA 1.44±0.01aA 68.35±0.1aA 19.24±0.64aA 0.24±0.01aA 0.06±0.02aA 0.21±0.01aA
   T2 9.51±0.4aA 0.62±0.13aA 0.02±0.0aA 0.05±0.01aA 1.44±0.04aA 68.23± 1.0aA 19.88 ± 1.2aA 0.24±0.01aA 0.07±0.01aA 0.27±0.04aA
  ANOVA C * ns ns ns * * * ns ns ns
   T ns ns ns ns ns ns ns ns ns ns
   C*T ns ns ns ns ns ns ns ns ns ns

palmitic acid (C16:0); palmitoleic acid (C16:1); margaric acid (C17:0); Heptadecenoic acid (C17:1); stearic acid (C18:0); oleic acid (C18:1); linoleic acid (C18:2); linolenic acid (C18:3); arachidic acid (C20:0) and gadoleic acid (C20:1)

Analysis of the fatty acid profile revealed four main fatty acids: oleic acid (C18:1), linoleic acid (C18:2), palmitic acid (C16:0), and stearic acid (C18:0) (Table 8). Oleic acid was dominant (68% of the total content), followed by linoleic (19% of the total content), palmitic (9% of the total content), and steric acids (1% of the total content). Our findings matched with Acar et al. (2017), reporting that main fatty acids found in pistachio were oleic, linoleic, and palmitic acids. Oleic acid ranged from 58.75% in cv. Ohadi to 68.70% in cv. Elguetar. Our results for the oleic acid content (58–68%) in pistachio samples were confirmed by previous studies (Arena et al., 2007; Noguera-Artiaga et al., 2020a). In the same line, Ghrab et al. (2010) reported that oleic acid was the main monounsaturated fatty acid, the total contents of saturated and unsaturated fatty acids being constant at 10% and 89%, respectively, and other fatty acids were determined in traces. Cv. Ohadi showed the lowest value of oleic acid (59.0; 58.7, and 59.4 with treatments T0, T1, and T2, respectively). Linoleic acid was the dominant polyunsaturated fatty acid, varying from 19.49% in cv. Elguetar to 28.75% in cv. Ohadi. Hence, the extracted oil from cv. Ohadi had higher content of linoleic acid (28.62%, 28.75%, and 28.52% with treatment T0, T1, and T2, respectively). Palmitic acid was the main saturated fatty acid ranging from 8.85% in cv. Elguetar to 10.13% in cv. Ohadi. Regarding stearic acid, it was found as a minor saturated fatty acid in pistachio kernels, ranging from 0.8% in cv. Ohadi to 1.52% in cv. Elguetar. Our results revealed that both cv. Ohadi and Elguetar had the most interesting fatty acid compositions among the studied cultivars. Statistically, neither of the treatments nor the ‘cultivar × treatment’ interaction (C × T) showed significant results; the only significant differences (p < 0.05) observed among cultivars were for four main FAMEs (oleic acid, linoleic acid, palmitic acid, and stearic acid).

Sensorial analysis

Sensory attributes of nuts, such as color, odor, size, sweetness, acidity, and hardness, were studied to assess their organoleptic quality and meet consumer preferences (Figure 5). These attributes influence the consumer’s sensory experiences, contributing to the overall perception of product. As expected, irrigation treatments significantly (p < 0.05) affected the sensory features and consumer’s global preferences. Pistachios grown with treatments T0 and T1 gained higher values of the most studied attributes, showing statistically significant differences (p < 0.05) with treatment T2. Our findings matched with those of Noguera-Artiaga et al. (2020a), studying sensorial properties of pistachios under RDI and reporting that pistachios under treatment T1 were the most appreciated ones. In addition, an international consumer study on the same topic indicated that the kernels resulting from moderate RDI applied during stage II had a higher intensity of sensory attributes and a greater level of satisfaction among consumers than the kernels obtained from well-watered trees or from those exposed to severe RDI during stage II (Noguera-Artiaga et al., 2016).

Figure 5. Sensorial analysis of salted and roasted (SRP) nuts of four pistachio cultiars grown under RDI treatments. Abbreviations: M = Mateur, E = Elguetar, K = Kerman, O = Ohadi. T0 = well watered, T1 = regulated deficit irrigation treatment, and T2 = stressed treatment.

Regarding nut color (Figure 5A), cv. Ohadi showed the highest values with irrigation treatments T2 and T0. Cv. Mateur with treatment T0 (7.5) had the highest value of sweet taste (Figure 5B). In the present study, sour taste (Figure 5C) showed a different trend, with treatments T0 and T1 having less sour taste than treatment T2 samples. The highest value of sour taste (6.5) was observed in cv. Mateur for treatment T2.

The nut size was cultivar-dependent, with cv. Ohadi demonstrated the highest value for treatment T0 (Figure 5D). Cv. Ohadi showed the highest value of nut hardness (Figure 5e) for treatment T0, with no significant difference compared to treatment T1.

The highest score for the roasted odor resulted in cv. Mateur grown for two water regimes of T0 and T1 (Figure 5f). The sweet/almond odor was also noted in cv. Mateur for two water regimes of T0 and T1 (Figure 5g). Considering global satisfaction (Figure 5h), which defines the final opinion of consumers about the overall quality of samples, all the studied cultivars grown under treatment T0 obtained the highest score, followed by treatment T1, which received water restriction during stages I and II of nut development, whereas treatment T2 was statistically different from both treatments T0 and T1.

The sensorial analysis performed in this study showed that cv. Mateur and Ohadi grown with treatments T0 and T1 were the most appreciated varieties among consumers. The roasting process had a significant impact on the sensorial quality of pistachio nuts. Roasted nuts from cv. Ohadi and Mateur grown under 100% ETc water regime were the most appreciated nuts, followed by treatment T1 nuts. Rodríguez-Bencomo et al. (2015) reported that the roasting process makes the pistachio commercially viable and valuable as it improved nut’s hallmark sensory characteristics, such as flavor, color, odor, and texture.

Nuts of local cv. Mateur were highly appreciated by consumers. Ojeda-Amador et al. (2018) reported that cv. Mateur presented a marked green appearance and higher intensity of the roasted nuts attribute and were appreciated for their flavor, intensity, and the persistence of pistachio aroma in the mouth. Regarding the roasted and sweet/almond odor, the resulting acceptability was confirmed by Noguera-Artiaga et al. (2016) and Ojeda-Amador et al. (2018).

Analysis of principal components

The multivariate analysis of data permitted the reduction of variables to two principal components, PC1 and PC2, revealing an interesting grouping of the studied cultivars under RDI strategy (Figure 6a). Depending on the water regime, the studied cultivars were distributed into four groups. Cv. Mateur, Elguetar, and Ohadi, grown with treatments T0 and T1, occupied the positive side of PC1 and PC2. These cultivars occupied the negative side of PC2 if subjected to severe drought stress (treatment T2). Cv. Kerman subjected to treatments T0 and T1 occupied the positive side of PC2 and the negative side of PC1. Cv. Kerman under severe drought stress (treatment T2) occupied the negative side of both PC1 and PC2.

Figure 6. Principal component analysis of main agronomical and biochemical pistachio nuts and oil quality of the four studied cultivars under RDI treatments: (treatment T0) control (100% ETc); (treatment T1) regulated deficit irrigation RDI (50% ETc during stage I and stage of nut development and 100% ETc during stage III); (T2) stressed treatment (50% ETc). Values are means (n = 3) ± SE. Abbreviations: TCSA = trunk cross-sectional area; FW = fresh weight; DW = dry weight.

The two principal components presented 61.0% of total variability. The first principal component PC1 showed 35.52% of the observed variability and separated the cultivars based on biochemical traits, fatty acid profile, composition, and size of nuts.

According to a PCA biplot, size, fat content (FC), C18:1 content, total phenols in oil, and carbohydrates of nuts were positively correlated to PC1 whereas absorbance at a wavelength of 270 nm (K270), chlorophylls, and C18:2 content were negatively correlated to PC1. Parameters such as biochemical traits, oil quality, and composition of nuts explained PC1 separation in a better way (Figure 6b). Principal component PC2, explaining 25.57% of total variability, was able to separate cultivars depending on water regime. Hence, treatment T2 occupied the negative side of PC2 whereas treatments T0 and T1 occupied its positive side. Among all the traits that contributed mostly to PC2 separation were phenolic compounds and the nutritional components of pistachios, with split nut and C18:1 being the only two parameters showing a negative correlation (Figure 6B).

Conclusions

The moderate water stress generated by RDI (treatment T1; 50% ETc during fruit development stages I and II, followed by full irrigation at 100% ETc during stage III) maintained nut organoleptic quality as compared to control trees. Water restriction applied in treatment T2 (50% ETc) during all growing seasons decreased nut composition and biochemical compounds. Cv. Ohadi presented nuts with higher dimensions and higher content of carbohydrates, ash, fiber, and proteins under three water regimes. Cv. Mateur and Ohadi presented high sensorial quality and were more accepted by consumers. Cv. Mateur appeared suitable for high-density planting under semiarid conditions. In the present study, the RDI irrigation treatments did not affect fatty acid profile. Oleic, linoleic, palmitic, and steric acids were the main components. Higher contents of volatile compounds were observed in pistachios roasted under stressed treatment T2 (50% ETc); hence, terpenes were abundantly found in non-irrigated pistachios. Oil yield of pistachio nuts was improved under treatment T2. Treatment T1 (RDI) reduced water supply by 20% during stages I and II of nut development, thus increasing water use efficiency without compromising yield and nut quality. Our results suggested that the RDI water management strategy could be applied in pistachio orchards grown under arid and semiarid conditions.

Acknowledgments

The authors thanked Boutheina Fridhi, Chaima Maamri, Boutheina Hajlaoui, and Dhiaa Miri for technical assistance and support, and Prof. Antonella Verzera for her helpful advice. Authors also thanked the staff of Aroma and Sensory Laboratory (ASLab) of the University of Messina for the analysis of volatile compounds.

Author Contributions

Walid Abidi and Rawaa Akrimi: conceptualization, data curation, formal analysis, and writing of original draft and review & editing. Valeria Rizzo: formal analysis, and writing of original draft and review & editing. Fabrizio Cincotta: data curation, formal analysis, and writing of original draft. Antonella Verzera: resources, supervision and writing and review & editing. Giuseppe Muratore: resources, supervision, and writing and review & editing. All authors read and approved the final manuscript.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Ethics and Consent

Panellists were informed about the conducted study and they agreed to the publication of the results of their sensorial modules. They were fully aware of the implications of publication and accepted any associated risk. All collected forms were anonymous. None of the participants was identified based on the details or images contained in the paper.

Conflict of Interest

The authors declared that they had no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data Availability

Data are available on request.

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