effect of edible composite coatings on shelf life of roasted pistachio nuts

introduction : pistachio (pistaciavera l.) is a tasty nut and a good source of nutrients. ithas a high content of numerous beneficial nutritive and bioactive compounds such as proteins, carbohydrate, moisture, vitamins, minerals, fiber and other micronutrients compounds, but the most exceptional components are the amount of fats and especially unsaturated fatty acids. therefore, this nut is highly susceptible to rancidity, especially after roasting. despite the high quality, raw pistachio and pistachio processing industry at iran, export of roasted and packaged pistachio, due to low shelf life and drastic changes intaste, is not very successfull. an effort was made to investigate the efficacy of gelatin in comparison with carboxymethyl cellulose (cmc) as edible coating to retard fat oxidation in roasted pistachio. materials and methods:five coating formulations were investigated in this study as follow: a) gelatin (4% w/v) + ascorbic acid (1% w/v): tga, b) cmc (1% w/v)+ ascorbic acid (1% w/v): “tca”, c) ascorbic acid (1% w/v): “ta”, d) gelatin (4% w/v) + cmc (1% w/v) + ascorbic acid (1% w/v): “tcga” and 5) control sample (uncoated sample): “tco”.roasted pistachio nuts were coated by dipping the nuts in the coating solutions. for each treatment, 100 gram of pistachio nuts were packaged (bopp/al/cpp, 80 micron plastic bags) in triplicate. the physicochemical analysis included measurement of free fatty acid (ffa), peroxide value (meq.o2 kg-1),hardness (n), moisture (%) and the sensory evaluation (texture, rancidity, taste and overall acceptability) were performed on coated and uncoated pistachio nuts stored at 35 and 50 °c. the nuts were sampled on the 0th, 1st, 2nd and 3rd month of storage. data was analyzed using minitab 16. analysis of variance (anova) and general linear models (glm) procedure wereused to compare the mean values of each treatment and significant differences between the means of parameters were determined based on the results of the tukey’s multiple range test (p 0.05).ffa content of tcga sample was significantly lower than other samples.the highest protection, according to these criterions, was provided by gelatin-cmc coating containing ascorbic acid.the control samples exhibited more bitterness and off flavor than the coated samples, seemingly on account of chemical reaction and second products of oxidation content. instrumental and sensory hardness of pistachio nuts which were coated with gelatin and/ or cmc (tca, tga and tcga) were significantly (p<0.05) higher than control and ta samples. the highest hardness was observed in tca sample buton the otherhand, uncoated sample (tco) showed the lowest hardness.the effect of storage time on hardness was also significant (p<0.05). hardness in control samples increased during storage while that of gelatin and or cmc coated pistachio showed decreasing trend.the moisture content of cmc and gelatin coated pistachios were more than control samples. statistically significant different were recorded for color of coated and uncoated pistachio nuts during 3 months of storage which score of color for control sample was higher than other samples and lowest score corresponding to ta samples. in other words, use of ascorbic acid lonely or in the coating matrix caused reduction of sensory evaluation of color. conclusion:the results of this study showed that edible coatings based on gelatin and cmc containing ascorbic acid protect roasted pistachio from oxygen and delay lipid oxidation. gelatin and cmc coating increased instrumental hardness and sensory firmness of pistachio but provided positive sensory preference compared to the control by protection pistachio nuts against lipid oxidation during the storage. therefore, use of gelatin-cmc coating containing ascorbic acid as a commodious coating has a good potential for reduction in the rate of oxidation and subsequently increase of shelf life of pistachio nuts and probably other food products containing a high lipid proportion, while gelatin and cmc edible coating did not adversely affect ontotal acceptance of the product.