effect of atmosphere condition of packaging on physicochemical, microbial and sensory properties of dried pistachio (ohadi variety)

introduction:pistachio (pistaciavera l.) is a tasty nuts and a good source of nutrients. during the last decade, the worldwide trades of pistachio have increasing trend, likely reflecting on the increase in consumers demand for this nuts. the high oil and essential fatty acid contents of the pistachio kernel is important from a nutritional point of view. however, high unsaturated fatty acids content makes pistachio nuts susceptible to oxidation and consequently off-flavors and off-aromas during storage.mold growth and the production of aflatoxins is another food-safety concern about pistachio nuts. lipid oxidation and fungal growth can be controlledby using an appropriateatmosphere in packaging.therefore, the main objectives of this study were to determine the effect of modified atmosphere(ma) compared with vacuum and air condition packaging on physicochemical, microbialandsensory properties of raw dried pistachio nuts (ohadi variety) in an accelerated storage conditions at 30±2°c and 50°c for 12 weeks. material and methods: the pistachio nuts were treated with 3 different system packaging, these treatment includes modified atmosphere packaging (map at 88% n2; 10% co2 and 2% o2), vacuum packaging and air condition packaging. the pistachio nuts were packed in five-layerpouches (2 pe+ 2 pa+1 glue :80 microns)and stored in triplicate at 30°c and 50°c for12 weeksand they were sampled every four weeks. oil from pistachio kernels for peroxide, and fatty acid assay were extracted by cold extraction and n-hexane was used as extraction solvent. peroxide value (meq.kg-1) of the extracted oil was determined by spectroscopic absorbance reading at 500 nm. free fatty acids (%), as oleic acid percentages in oil samples, were determined using the titration method. moisture content (%) was determined by drying 5 g of ground kernels at 103±2 °c until constant weight. the mouldcontent (log cfu/g) of pistachios were performed according to the iran standard method. the textural analysis of the pistachio nuts were performed using cylinderprobe (diameter: 20 mm) at test speed 50 mm/min and deformation of 4 mm for samples. fracture force (n) and hardness (n) parameters were measured to evaluate textural properties ofpistachio nuts samples.sensory evaluation was carried out by a 20 member trained panel (10 females and 10 males). sensory attributes evaluated included color, firmness, rancidity and overall acceptability on 5 point hedonic scale, whit 5 for excellent and 1 for very dislike. analysis of variance (anova) was carried out using the least significance difference(lsd) test (p<0.05). the data wereanalyzed using the minitab 16 software. results& discussion: observations indicated that the packaging conditions hadno effecton themoisture content ofraw dried pistachio nuts.but, the study of moisture content in different storage temperature showed that the moisture content of samples in both temperature were extremely decreased after 4weeks storage, but after this time the trend of reducing moisture was stopped at 30 °cand the moisture ofpistachios were reachedto equilibrium with ambient moisture, while the reducing trend of pistachio nuts moisture were continued at the higher temperature (50 °c) until 60 days after treatment.this was attributed to higher capacity of warm air to absorb moisture. therefore, the significant differences in final moisture content of dried raw pistachio nuts were observed in different temperature during 12 weeks. the peroxide values andfree fatty acid of ma and vacuum packaging samples were significantly lower than these paramours in air condition packaging (p<0.05). the lower oxygen content of these atmospherecan reduce the rate of lipid oxidation in the pistachio nuts. also, decreasing the oxygen content of package atmosphere (ma and vacuum packaging) was resulted in decreasing in mould content of pistachio. in addition, higher co2 content of map have an antifungal effect in pistachio nuts and subsequently the lowest fungal contamination was observed in map. texture profile analysis (tpa) revealed that modifiedatmospherepackaging decreases fracture force and these pistachio had better texture than two other samples. however, there was no significant difference between samples.also thesensory evaluation demonstrated that ma and vacuumpackagingimprovedcolor, firmnessandoverallacceptance ofpistachio nuts. conclusion:it is concluded that modifiedatmospherepackagingcan increase shelf life of raw dried pistachio nuts by reducing lipid ox idation and fungal contamination as well as improving sensory quality of pistachio nuts. then it is recommended to use map alone or in combination with other protective strategies to improve quality and increase shelf-life of pistachio nuts.