Study Of Drying And Fresh-keeping Treatments On Quality Of Walnut (Juglans Regia L.)

Walnut is one of the most significant industries in China,which possess the maximum output and planting area in the world.But because of its high fat content,its quality degraded as a result of the oxidation and rancidity of oil,which brought up huge economic losses and healthy risk for manufactures and consumers.In the present work,the changes of oil storage quality,fatty acid composition,LOX activity,and antioxidant activity of walnut kernel were studied,usinge different methods of drying,storage or fresh keeping of walnut.The results were as follow:1.The iodine value,peroxide value,saponification value,acid value,reducing power,DPPH· clearance,tannin and total phenol content of different regions of the thin skin and leatheroid walnut were determined.It was found that there were significant differences in iodine value,peroxide value,saponification value and acid value of different regions of the walnut?P < 0.05?.Tannins and total phenol content appeared obvious difference,however,there was no significant differences in reducing power,and DPPH· scavenging activity?P > 0.05?.2.Fresh walnuts were dried by three different methods?sun drying,direct oven drying or intermittent oven drying?,then,stored under the room temperature or 4 ? after 90 d,rspectively.Results showed that under all drying and storage methods,acid value,peroxide value,and saponification value tended to rise,but walnuts in intermittent oven drying and stored under low temperature had better quality attributes than those of other samples.In addition,the acid value of walnut by intermittent oven drying was only 0.6 mg/g,and the acid value storaged under 4 ? after 90 d was 1.1 mg/g,respectively.Oleic acid content in walnut of sun dried was highest as 21%,however,only 61% linoleic acid was detected,and ratio of oleic acid and linoleic acid?O/L?was significantly higher than other drying processing?P < 0.05?.LOX activity in the process of drying and storage presented downward trend after rising,and the minimum value of 0.429 kat/mg found in sun dried walnuts.Low temperature can significantly inhibited LOX activity,sun dried walnut under 4 ? storage after 90 d was significantly lower than other samples?P < 0.05?.Antioxidant capacity of sun dried walnut was generally low,but in the storage period,antioxidant capacity of different samples did not appear significant difference?P > 0.05?.3.Green walnut was processed by 1-MCP and ClO₂ or NaHSO₃,control,and 1-MCP alone treatment,samples were stored under 4 ? for 30 d.Results showed that 1-MCP combined ClO₂ or NaHSO₃ treatment effectively reduced the acid value and peroxide value of green walnut,and inhibited LOX activity,hence delaying fruit senescence.1-MCP + ClO₂ can promote the synthesis of phenolics,and total phenol content of walnut by ClO₂ treatment in 18 d was 4.28 mg/g,meanwhile it enhanced the reducing power and DPPH· and O₂^-· scavenging activity.4.Green walnuts with the combination of 1-MCP + NaHSO₃ treatment and 30,40,60 ?m PE package,effectively reduced the acid value and peroxide value,and inhibited the LOX activity,thus delaying fruit senescence and enhance its reducing power,DPPH· and O₂^-· scavenging activity and total phenol content.Lipid oxidative rancidity inhibitory effect of walnut in 30 ?m PE package was worse than 40 and 60 ?m package?P < 0.05?.The results indicated that walnut packaged in 60 ?m PE bags with 1-MCP + NaHSO₃ treatment showed the best effect to maintain the quality.