Study On The Factors And Regulation Of Dried Noodles Lipid Rancidity

Dried noodles(DN)have the advantages of lower water content,ease of preservation and convenience,which are popular with consumers and have a broad market demand.However,DN have obvious drawbacks with regard to the long-term storage since lipid rancidity occurs,generating unpleasant acid off-odors and raising safety concerns.Many factors could influence DN lipid rancidity.This paper will disscuss the factors from three aspects: raw materials,processing and storage conditions.Firstly,the effect of wheat flour freshness on lipid rancidity of DN during storage was studied.Wheat flour(WF)was stored for 0,4,8 and 16 weeks to obtain WF with different freshness.And then they were made into DN for storage.Results showed that the free fatty acid value(FFA)of stored WF increased significantly(p<0.05),revealing that lipid hydrolysis occurred and freshness decreased;And the lower the WF freshness was,the more the FFA and linoleic acid content were decreased during processing.During storage,the FFA of dried noodles made from wheat flour stored for 8 weeks(DN-WF8)and 16 weeks(DN-WF16)significantly(p<0.05)increased.The linoleic acid content of DN-WF16 reduced and the content of aldehydes and acids were higher,showing lipid oxidation.Overall,WF freshness decreased,causing lipid hydrolyzed and oxidized easily during processing and storage.Secondly,the effect of wheat flour processing degree on lipid rancidity of DN during storage was studied.Results showed that during storage,total lipid(TL)and bound lipid(BL)content decreased,free lipid(FL)content decreased,then increased and then decreased,indicating lipid loss.FFA increased significantly(p<0.05),and the lower the WF processing degree was,the higher the lipid hydrolysis levels and rates were.Endogenous lipase activity decreased,but dried noodles made from low processing degree wheat flour(DN-LPDWF)were still higher than other groups.The linoleic acid content increased and then decreased(p<0.05),and the DN-LPDWF group had the lowest content.The lower the WF processing degree was,the greater the increase in the content of acetic acid,hexanoic acid and nonanoic acid,and the higher the content of free radicals,indicating the faster rate of lipid rancidity.In summary,as the WF processing degree decreased,lipid hydrolysis and oxidation occurred more easily in dried noodles during storage.Thirdly,the effect of bran and germ addition on DN lipid rancidity during storage was studied.The results showed that the FFA of DN: bran and germ mixed addition group> bran addition group> germ addition group> blank group;Hexanoic acid content increased during storage and the mixed addition group was higher.Conclusions could be made that mixed addition of bran and germ would produce synergistic effects,which made lipid hydrolysis and oxidation levels higher than that of the separate bran and germ addition group,and the effect of bran was significantly higher than that of germ.Fourthly,the effect of processing(hydration,sheeting and drying procedures)on DN lipid rancidity was studied.Results showed that hydration and sheeting procedures leaded to FL converting to BL,changing lipid profile.Meanwhile,FFA and polyunsaturated fatty acid(PUFA)content decreased(p<0.05),peroxide value(PV)and free radical content increased,indicating lipid in the dough and noodles oxidized.The decrease in FFA and PUFA content during drying procedure also reflected lipid oxidation.Lipase was stably during processing while lipoxygenase activity decreased.The content and types of volatile aldehyde and acids increased.Overall,processing especially the hydration and sheeting procedures changed lipid profile,induced lipid oxidation and lowered the lipid stability in dough and dried noodles.Fifthly,the effect of wet broken noodles(WBN)and dry broken noodles(DBN)on DN lipid rancidity during storage was studied.The results showed that the total plate count of WBN increased significantly(p<0.05)during storage.The initial FFA value of dried noodles with the addition of wet broken noodles stored for 0 h,8 h and 16 h(DN-WBN0,DN-WBN8,DNWBN16)was significantly(p<0.05)lower than that of DN-WBN24.Meanwhile,during storage the FFA value of DN-WBN24 was significantly(p<0.05)higher than other groups.It was revealed that adding WBN within 16 h had little effect on DN lipid rancidity,while adding WBN stored for 24 h would significantly affect the storage stability of DN.Microbial effects would be the main reason.In addition,the FFA value of DN at 0,4 weeks had no significant difference(p>0.05)between 0%,4% and 8% DBN addition groups.After 8 weeks,the FFA value of the 8% addition group was significantly(p<0.05)higher than that of the 4% addition and non-addition groups.It could be concluded that the addition concentrations of DBN had little effect on the DN lipid in the short-term storage,but during long-term storage,the higher concentrations of DBN addition would reduce DN lipid stability.Lastly,the effect of packaging materials(Paper+POF,PET,PA/PE)on DN lipid rancidity during storage was studied.The results showed that moisture content increased,the FFA value increased first and then decreased,and the linolenic acid content decreased.The changes in Paper+POF packaging group was the greatest,while the differences between PET and PA/PE groups were little.To conclude,packaging materials with high moisture and oxygen permeability would make DN absorb water vapor and become damp,thereby intensifying lipid hydrolysis and oxidation.