Background: Fresh pistachio can be affected by physiological and biochemicalchanges both during harvest and after harvest, and its optimum duration ofstorage cannot therefore be prolonged. Materials andmethods: In order to maintain the quality offresh pistachio fruits (Pistacia vera L. Ahmad Aghaei),carboxymethyl cellulose at different concentrations accompanied by differentconcentrations of Zataria multiflora essential oil was used to producean edible coating.
The effects of these combinations were examined on thequality, shelf life, and sensory properties of the fresh fruit during a storageperiod of 32 days (3±1°C, 85±5% RH). Results: The results of sensory and instrumental tests during storage ondays 8, 16, 24, and 32 showed that coated samples with 1.5% (w/v) carboxymethylcellulose used in combination with Zataria multiflora essential oil hadthe longest shelf life compared to the other treatments.
Among the treatmentscontaining 1.5% (w/v) carboxymethyl cellulose, the lowest weight loss and thehighest kernel carbohydrate, total soluble solid, phenolic compounds, andantioxidant activity were observed in the treatments containing 1.5% (w/v) carboxymethylcellulose accompanied by 0.4% (w/v) and 0.2% (w/v) Zataria multifloraessential oil.
Conclusion: Application of 1.5% (w/v) carboxymethyl cellulose in combinationwith 0.4% (w/v) and 0.2% (w/v) Zataria multiflora essential oileffectively maintained the quality of fresh pistachio during the 32 days of storage.
Keywords: Fresh pistachio; edible coating; carboxy methyl cellulose; essentialoil; Zataria multiflora 1. IntroductionPistachio is an agricultural product with high nutritional value. Thisfruit is a good source of vitamins A, B1, B2, B6,and E, and minerals such as iron, phosphorus, selenium, zinc, and fatty acids.Fatty acids are precursors in the synthesis of prostaglandins and ultimatelyprevent the accumulation of erythrocytes in the blood (1).
Recently, the application of natural and biodegradable coatings instead of artificial waxes has increased (2). Edible coatings consist of a thin layer of nutrientsthat form directly on the fruit’s surface. These coatings have the potential tocreate a selective barrier to moisture, CO2, and oxygen.
Edible coatings maycontrol the internal atmosphere of the fruit, minimize the respiratory rate ofthe product, and delay the evaporation of water and moisture loss (3). Edible coatings increase the shelf life of fresh fruits and vegetables byreducing metabolic processes and microbial growth (4). Cellulose derivatives are linear polysaccharides composed of ?-1 and 4 glucoseunits with methyl, hydroxypropyl, or carboxyl substitutions.
Carboxymethylcellulose is one of the most common cellulose derivatives used in thepreparation of edible films (5). It is linear, has a long chain, and is awater-soluble, anionic, and non-allergenic polysaccharide (5). This coating, incombination with antioxidant and antimicrobial agents, can effectively preventthe growth of fungi and microorganisms (5).
The respiration rate isone of the major factors contributing to the postharvest loss of fruit (6). Azarakhsh et al. showed that the respirationrate of fresh-cut pineapple samples coated with an edible alginate coating was significantlylower than the uncoated samples during storage (6). This reduced respiration rate is achieved bythe coating creating an internal modified atmosphere which reduces the exchangeof carbon dioxide and oxygen between the environment and the coated fruit (7).Also, Asgar at al.observed that papayas coated with chitosan showed a lower respiration rate andethylene production during storage (8).
Reductions in respiration rate andethylene production as a result of edible coating has also been reported bymany researchers reporting research on various fruits, such as grapes,strawberries, papayas, tomatoes, and mangos (9). The application of this cellulose coating on pecancan limit the contact of oxygen with kernels and the exchange of gases by acting as a barrier. This results in a reducedoxidation of lipids in the kernel (10).
Edible coatings have the potential to carryactive ingredients, such as anti-browning agents, coloring products,antimicrobials, and essential oils (11). The results of Raeisi et al.’s study showed that edible carboxymethyl cellulose coatingwith the essential oil of Zatariamultiflora and grape seed extract is very effective in reducing the undesirablechemical reactions in fish meat during storage (11). According to the research conducted by Dhall Group,edible coatings should basically be resistant to water. They should not showdestructive behaviors on O2 or cause the accumulation of excessiveamounts of CO2 (2). Edible coatings should have minimum permeabilityto water vapor, and their presence is expected to improve the fruit appearanceand gloss, while preventing the fruit from becoming sticky. Edible coatingsshould be economical and optically transparent during the time of storage.
Therefore, this study aimed to evaluate the effects of differentconcentrations of carboxymethylcellulose (CMC) edible coating in combination with different concentrations of Zataria multiflora essentialoil on weight loss, total soluble solids (TSS), carbohydrate, phenolics,antioxidant activity, and sensory properties of fresh pistachio during 32 daysof storage.2. Materials and Methods2.1 Materials2.1.1. FruitThis study was conducted on an important commercial pistachio cultivarcalled Ahmad Aghaei.
The samples were prepared from a pistachioorchard located in Pistachio Research Center in the city of Rafsanjan. 2.1.2. CoatingsCarboxymethyl cellulose as an edible coatingand glycerol as a plasticizer in the edible coating were supplied from Sigma-Aldrich(Steinheim, Germany).
The Essential oil of Zataria multiflora, was purchased from BarijEssence (Esfahan, Iran). 2.1.3.
Preparation of samples and treatmentsThe fresh AhmadAghaei pistachios were harvested at maturity and transferred to the laboratory,and pistachio fruits werethen isolated from the cluster in order to treat. The coating solution was prepared following themethod used in Arnon et al. (12).
Briefly, a solution of an appropriate amountof carboxymethyl cellulose powder in distilled water was prepared by heating at80°C and stirring to form a clear solution. Then, 1% (w/v) glycerol was addedto the solution as a plasticizer. Different concentrations of Zataria multiflora essential oil (0.0, 0.2, and 0.
4% (w/v)) were added tothe mixture. Finally, all formulations were homogenized for 10 min. 2.1.4.
Treating and storage of fruitsFresh Pistachios were immersed in coating solutions for 3min and were then air-dried at room temperature for 1 min. They were then sortedto 200-gr packs in each polypropylene dish and stored at 3±1°C and 85±5% RH for32 days. Fruits without coating and essential oil were also placed at the samecondition as control. Weight loss, total soluble solids,carbohydrate, phenol, antioxidant activity, and hedonic test were evaluated after 0, 8, 16, 24, and 32 days of storage. 2.2.
Parameters assay2.2.1. Weight lossFruit weight loss percentage was measured using thefollowing equation (Eq.
1): (Eq. 1) 2.2.2.
Total phenolic compounds and total antioxidant activityTo estimate the phenolic value of the pistachio, the method reported by Singletonet al. (13) was used. Briefly, 0.5 gr of thekernel was homogenized with 3 mL of 85% (v/v) methanol, and the resultingmixture was then centrifuged at 10,000 rpm for 15 min.
Then, 150 µL of thesupernatant was transferred to a test tube where 75 µL of Folin-Ciocalteuphenol reagent was added. After an incubation period of 5 min, 600 µl of 7% (w/v)Na2CO3 was added to the solution, which was then mixedwell and kept in dark for 1.5 h. The samples were vortexed. Their absorbancewas then measured at 760 nm.Antioxidant activities were measured using the method presented by the Brand-Williams Group (14). To do this, an extraction procedure similarto the one applied for phenolic value was conducted. After the extraction, 250?l of the supernatant was mixed with 250 ?l of distilled water andcentrifuged for 10 min.
Then, 75 ?l of the combined solution was mixed with2.925 ml DPPH 85% (w/v), and the absorbance of each solution was recorded at517 nm. After incubation in dark for 30 min, the absorbance was again measuredat the same wavelength.
2.2.3. Total soluble solids (TSS) and carbohydrateThe TSS valuewas measured as an average of 10 fruits in each replicate and assessed by adigital refractometer (ATAGO,PAL-1model Japan). To determine carbohydrate content, 0.5 g of pistachio ash (without oil) washomogenized with 5 ml of 95% (v/v) ethanol.
The extraction was repeated twice using 5ml of 70% (v/v) ethanol, and the obtainedmixture was then centrifuged at 3,500 rpm for 20 min. After that, 100 ?l of thealcoholic extract was mixed with 3 ml of freshly prepared anthrone (150 mg ofanthrone in 100 ml of sulfuric acid 72% (v/v)). The solution was placed in awater bath at 90°C for 10 min.
Then, absorption rate was measured at 625 nm (15). 2.2.4. Sensory analysisFor sensory analysis, eight trained panelists were selected from the Pistachio ResearchCenter staff. The sensory evaluation form had a score scale from 0 to 15, thelowest to the highest admission. The panelists assessed the parameters hull color, pistachiocolor, taste, flavor, strange flavor and odor, juiciness texture, and overallvisual and flavor acceptance based on the evaluation forms.
2.3.Statistical analysisThis experimentwas performed with three factors in a factorial design based on a completelyrandom design. Each value is the average of three replications. Sources ofvariation were CMC edible coating, Zataria multiflora essential oil, and the duration of storage. The experimental data were subjected to analysis of variance(ANOVA) by using the SAS 9.
1 statistical software. 3. Results 3.1. Weight lossAs depicted in Fig.1, the weight loss of all coated fruits increased after32 days of storage.
The highest percentages of weight loss were observed in thecontrol (8.28%) and the fruits coated by 0.2% (w/v) Zataria mulrifolra essential oil (9.06%) and the lowest was associated with1.5% (w/v) CMC. In 1.5% (w/v) CMC edible coating fruits, the weight lossgradually decreased with increasing the Zataria mulrifolra essential oil concentration, and finally 1.5% (w/v) CMC treatment incombination with 0.
4% (w/v) Zataria mulrifolra essential oil showed theleast weight loss (4.43%) after 32 days of storage. 3.2.
TSS and carbohydrate contentThe highest and the lowest TSS% were observed in the control and the fruitstreated with 1.5% (w/v) CMC, respectively (Fig. 2A). In the present study, thecoatings enriched with 0.2% (w/v) and 0.4% (w/v) Zataria mulrifolra essential oils were more effective in reducingmetabolic processes in fresh pistachio compared with the other treatments.The results indicated that there were significant differences in thecarbohydrate content between uncoated and coated fruits during the storageperiod (Fig.
2B). It was found that treatment with 1.5% (w/v) CMC enriched with0.2% (w/v) and 0.
4% (w/v) Zataria mulrifolra essential oil showed thehighest carbohydrate content in comparison with the other treatments in 32 daysof storage. 3.3. Phenolic and Antioxidant activityAs shown in Fig.
3A, the lowest and the highest contents of phenolics were observedin the control (140.15 mg gallic acid per 100 g fresh weight) and the fruits coatedwith 1.5% (w/v) CMC. Of the coatings containing 1.5% (w/v) CMC, the one enrichedwith 0.4% (w/v) Zataria mulrifolra essential oil showed the highest phenolics contents (221.59 mg gallic acidper 100 g fresh weight), which was found to be statistically significant.
Antioxidant activity of the kernel was significantly affected by thetreatment composition as well during storage (Fig.3B). During the storage period,the fruits treated with the coating containing 1.
5% (w/v) CMC and 0.4% (w/v)essential oil showed the highest antioxidant activity in comparison to the othertreatments. For example, on day 32, the fruits coated with 1.5% (w/v) CMC accompaniedby 0.
4% (w/v) essential oil showed 24.79 % antioxidant activity, while thecontrol sample showed 14.66 %. 3.4. SensoryanalysisSensoryevaluation was conducted based on hull color, taste, odor, strange flavor andodor, juiciness texture, and overall visual and flavor acceptance for bothcoated and uncoated samples during the storage period of 32 days at 3±1°C (Fig.
4). The incorporation of 0.2% (w/v) and 0.4% (w/v) zataria mulrifolraessential oil into the CMC-based coating formulation had desirable effects on thesensory attributes of the coated fruits. Of all the coatings, the one enrichedwith 0.4% (w/v) zataria mulrifolra showed more positive effectson the overall acceptability of samples (11.
41). 4. DiscussionIn 2012, the Wittaya Group reported that edible coatings containingplasticizers are good inhibitors for moisture loss, and they can specificallyreduce the rate of moisture loss from seeds (16). The weight loss of freshpistachios coated by the CMC in our study was consistent with the resultsreported by the Albanese Group in 2007 (17), who demonstrated that theimmersion of citrus fruits in CMC coating effectively reduced weight loss. Itwas suggested that the positive effect of this coating was capable of reducing respirationrate due to the development of an amorphous glass on the citrus surface which heldback water evaporation. In 2007, the Lins Group stated that edible coatingsprovided effective barriers against oxygen, carbon dioxide, and water vaportransmissions and, as a result, they could reduce moisture loss (18).
Also, in 2013, the Athmaselvi Group reported thattomatoes coated with Aloe vera showed a gradual decrease in the TSSduring storage (19), a result in line with the findings of our study. This maybe due to the break-up of pectin and carbohydrates, partial hydrolysis ofprotein, and decomposition of glycosides into subunits during respiration,which causes a decrease in the total soluble solids (19). Furthermore, the Athmaselvi Group reportedthat sugar content in coated tomatoes was higher compared to the correspondingcontrol, due to the controlled atmosphere around the fruit created by theedible coating that in turn was obtained by reducing respiration andtranspiration loss (19). Phenolic compounds are natural antioxidants that can befound in different vegetable sources (20). The relationship between the amountof the total phenolics and the antioxidant properties has been studied in manyfruits and vegetables (20). It is believed that phenolic components areconsiderably involved in the antioxidant capacity (20). The Guerreiro Grouppreviously reported that the antioxidant capacity of Arbutus unedo freshfruits increased when the fruits were treated with alginate edible coatingsenriched with eugenol and citral essential oils (4), which is in line with ourresults.
The decrease in antioxidant activity during storage may be attributedto the destruction of cell structures as the fruit undergoes senescence (21).Edible coatings may provide a barrier to reduce oxygen consumption andtherefore reduce oxidative processes (22). The antioxidant effects of someessential oil compounds may also contribute to the maintenance of antioxidantactivity in fruits (23). Furthermore, in 2008, the Oms-Oliu Group found that usingedible coatings was effective in reducing total phenolic compounds andantioxidant capacity in fresh-cut melon during storage (24). In 2015, the DashipourGroup reported that the highest total phenolic and antioxidant activity wasobserved in CMC films incorporated with Zataria multiflora essential oil(5). In our study, the increase in antioxidant activity was related to theenhancement of phenolics in the pistachio kernel.
Also, some researchers havestated that the accumulation of phenolic compounds can be a result of an increasein antioxidant activity (24-25). The addition of essential oils to edible coatings instead of the direct applicationof the essential oils can cause the oils to be released gradually. Thisimproves their performance and efficiency.
Our results are in line with those previouslyreported by the Khoshnodinia Group in 2013 who showed that the application ofantioxidant-gelatin combined with an edible coating on pistachio had greatereffects on the sensory scores in comparison with the absence of the antioxidant(26). Since edible coatings are usually eaten along with the fruits, investigationof their sensory properties is of great importance (27). The sensory resultsobtained in the present study are also in harmony with those reported by the Arnonand the Tzoumaki groups (12, 28).
In 2006, the Baldwin Group indicated that CMCcan influence the sensory parameters related to the pecan kernel (10). CMC-containingcoatings also improve the appearance and gloss of the coated fruit, maintain thefruit quality and flavors, and fully covers the fruit surface (28). Moreover, thiscoating is deemed economically affordable and is considered a homogeneous andtransparent material. Also, CMC-based coatings possess good stability and canbe easily prepared (28). Thymol and carvacrol are the most important and abundant components in thymeessential oil. These components belong to the group of phenols and haveantifungal properties (29).
It has been also reported that the phenoliccompounds available in thyme have inhibitory effects on the growth of Aspergillusflavus (30). In a study by the Baraiya Group in 2012, the application ofCMC in combination with clove essential oil effectively increased the shelflife of tomato by delaying the ripening of the fruit and postponing theirsenescence (31). 5. ConclusionThis studyshowed that the CMC edible coating enriched with Zataria multiflora essential oil can maintain the fruit quality of fresh pistachios during storage.
Furthermore, this treatment prevents excessive weight loss and improves thefruit quality in terms of phenolics, antioxidant activity, carbohydrates, andTSS. We concluded that using an edible coating containing 1.5% (w/v) CMC enrichedwith 0.4% (w/v) Zataria multiflora essential oil can extend the duration of storage andmaintain the quality of fresh pistachios for 32 days.