The Effects Of Storage Conditions And Processing Methods On The Quality Of Walnut

Walnut(Carya cathayensis Sarg.)is a unique woody oil tree species in China.It is the third-class national endangered plants,which has medicinal,health and beauty values.However,the external environmental conditions and internal factors will accelerate the oxidative rancidity,which will lead to the loss of their commercial character during storage and processing.At present,20% of the total production were lost because of the improper storage and processing conditions.This study intends to explore the optimum storage conditions and processing technology from the safety storage and high-quality processing of raw walnut,and the extension of shelf life of pecan kernel products.The result are as follows:(1)In order to investigate the effects of storage temperature on lipid oxidation,antioxidant activity and physiological activity of walnut,the raw Lin'an walnut was storaged at frozen(-18?),refrigerated(4?)and room temperature(25?)respectively for 6 months.The results showed that low temperature was conducive to inhibit lipid oxidation,lipase activity and respiration intensity;maintain antioxidant activity,antioxidant enzyme activity,and unsaturate fatty acid content;decrease the weight loss rate;and reduce the production of membrane lipid peroxides(MDA)during storage.Walnut storaged at 4? had better SOD,POD and CAT activity,reduced less production of membrane lipid peroxides(MDA)compared with Walnut storaged at-18?.However,Walnut storaged at-18 ? had better lipid quality,antioxidant activity and more unsaturated fatty acid content than walnut storaged at 4?.(2)In order to study different processing methods on the lipid oxidation,fatty acids composition and antioxidant activities of walnut,naked seed,hand-stripping and walnut kernel were used to process walnut from Lin'an city of Zhejiang Province in this experiment.The results showed that after processing the acid value and peroxide value of all samples showed a significant increase(P<0.05),and the content of total phenols content(TPC),total flavonoids(TFC),total tocopherol and unsaturated fatty acid had a significant decrease(P<0.05).Among the three processing methods,hand-stripping processing methods resulted in the lowest POV,that was 1.61 g/kg,the higest TPC,TFC,total tocopherol content,and unsaturated fatty acid content that was 6.16 mg/g,0.83 mg/g,52.10 mg/kg,21.22 mg/g,respectively,and the strongest antioxidant activity evaluated by reducing power and DPPH· assays.(3)In order to study the effects of storage condions on lipid oxidation,antioxidant activity and fatty acids composition in pecan kernel during storage,different methods were used to treat walnut including(PA / PE,dark treatment,no vacuum),(PA / PE,dark treatment,vacuum),(PA / PE,light treatment,no vacuum),(PA / PE,light treatment,vacuum)and(PET / PE,light treatment,no vacuum).The results showed that the peroxide value exceeded the high limit of edible vegetable oil hygiene standards in GB 2716-2005(0.25 g / 100 g)after 6 months storage except dark and vacuum co-treatment group.On the maintanace of peroxide value and anisidine value,the vacuum treatment was better than the dark treatment.In maintaining the acid value,total phenol content,flavonoid content,DPPH· assays,and unsaturated fatty acid such as oleic acid,linoleic acid and linolenic acid,the dark treatment was better than the vacuum treatment.There was no significant difference between dark and vacuum treatment in the effects of iodine value,reduce power,palmitic acid and stearic acid(P> 0.05).The packaging materials of PA / PE performed better than PET / PE during storage of pecan kernel.