The Effect Of Mold On The Fat Loss Of Walnut Kernels

In the process of storage and transportation,fresh walnut kernel is prone to be contaminated with mold,which will cause mildew.The type of mold that cause fresh walnut kernel to be moldy varies with seasons,growing conditions and walnut kernel varieties.Mold contamination will not only cause walnut kernel to go moldy and rotten,but also to go bad and rancid.The composition of walnut kernel could easily get physical and chemical change under oil rancidity,which would extremely reduce the commercial and nutritional value.Therefore,research on mold and its influence on oil rancidity will be a good guidance for controlling the mildew and reducing nutritional loss of walnut.In this paper,molds were separated from moldy walnuts kernel sourced from the Qinling Mountains,and then purified and identified.The dominant molds were inoculated on walnut kernel surface to explore its effect on walnut kernel mildew through measuring mold growth during different stages.The results were as follows:1.66 strains of molds were separated from moldy walnut kernel,and five genera of major molds,Fusarium,Alternaria,Aspergillus,Penicillium and Mucor,were confirmed through microscopic identification.Among these molds,there were 23 strains of Aspergillus(34.85%),20 strains of Mucor(30.30%),18 strains of Penicillium(27.27%),3 strains of Alternaria(4.55%),and 2 strains of Fusariun(3.03%).The first three genera were predominant molds,whose strains were roughly the same and accounted for 92.42%of total contamination.These dominant molds were inoculated on CA,CYA,ME A,and they were morphologically identified belonging to A.niger,P.citrinum,A.flavus and M.racemosus.2.Four kinds of dominant molds were inoculated on walnuts kernel with different water contents,and their growth was observed and analyzed.The results were indicated that,these molds could not grow on walnut kernel with the water content of 14%,but could grow on walnut kernel with the moisture content of 22%.Only A.niger and P.citrinum could grow on walnut kernel with the water content of 18%.3.Under these four molds contaminations,the pH value of walnut declined and then increased,LA activities offered upgrade firstly then descending the latter tendency.The activity of LOX,POV,AV showed a upward trend,while the content of proteins and the activities of SOD,CAT,POD all presented downtrend.There were significant differences compared with control groups(P<0.05).In terms of these changing trend,mold contamination accelerated walnut oil rancidity which varied with species,and the most destructive one was A.niger.4.A.niger was inoculated on walnut kernel to study the laws of oil rancidity.The results showed that,(1)the highest infection rate and worst oil rancidity were found in walnut kernel with a storage temperature of 35 ℃.The oil rancidity would be lightened but not controlled with temperature down to 25 ℃,and it could be controlled steadily at 15℃.(2)Water content of walnut higher or lower would both accelerate oil rancidity.For lowest rancidity,the moisture content of walnut should be controlled at 16%.(3)During storage,walnut oil rancidity occurred more easily at RH 92%than that of RH 65%,and the lower one was better.(4)A.niger was aerobic bacteria,thus walnut kernel should be sealed under nitrogen,stored in a cool and dark place to inhibit the growth of A.niger and decrease oil rancidity.