Study On Inhibition Of Lipid Rancidity In Dried Whole Wheat Noodles

Dried whole wheat noodles(DWWN)meet the needs of consumers for nutritional health and balanced diet,so it has a broad market prospect.However,the raw material for making DWWN—whole wheat flour(WWF)contains a large amount of unsaturated fatty acids(UFAs)and highly active lipid degrading enzymes.Coupled with the influence of multiple processing steps in the making of noodles.DWWN are prone to rancidity during storage,which affects the edible safety of the product.Based on this,this dissertation mainly studies the technology and means of superheated steam treatment(SST),extrusion treatment(ET),superheated steam combined with the control of key points in the process of making dry noodles to inhibit the lipid rancidity of DWWN,and provides a theoretical basis for the industrial production and popularization of DWWN.Firstly,the effects of SST on the lipid stability of WWF and DWWN were studied.After SST,the lipase and peroxidase(POD)of WWF were completely inactivated,and lipoxygenase(LOX)activity decreased by 95%;total tocopherols content did not change significantly(p>0.05).During storage,the increase of fatty acid value in the control WWF was 151-fold of that in the SST groups;the degradation of UFAs and the consumption of total tocopherols by SST at 190℃ for 5 s were less than those in the control WWF.SST significantly reduced the activities of lipase,LOX and POD(p<0.05),inhibited the growth of fatty acid value,the degradation of UFAs,and the consumption of tocopherols and tocotrienols in DWWN;the main volatile compound in the control DWWN was 2-pentylfuran,while the main volatile compound in the SST groups was hexanal.Among them,the UFAs and tocopherols of the DWWN treated with SST at 190℃ for 5 s decreased by 2.7%and 10.9%respectively after 12 weeks of accelerated storage,which were much lower than those of the control group(12.3%,41.4%).In conclusion,SST significantly inhibited the lipid degradation of WWF and DWWN during storage,and the effect of SST at 190℃ for 5 s had the best inhibition effect.Secondly,the effect of ET on the lipid stability of WWF and DWWN were studied.After ET,the activities of lipase,LOX,POD,fatty acid value,the content of UFAs and polyphenols decreased by 89.1%,85.4%,95.7%,28.6%,15.6%and 7%,respectively.After ET,the enzyme activities of WWF and DWWN decreased significantly during storage(p<0.05).After 12 weeks of accelerated storage,the increase of fatty acid value,degradation of UFAs,consumption of polyphenols in the control WWF were 5.2,19.6 and 8.5-fold than those in the ET-processed WWF,respectively;the relative content of 2-pentylfuran and n-hexanal of volatile compounds in the control WWF were 2.7 and 0.4-fold than those in the ET group.The increase of fatty acid value,degradation of UFAs,consumption of polyphenols and total volatile compounds in the control DWWN were 8.8,116,13 and 1.8-fold than those in the ET-processed DWWN,respectively;the relative content of 2-pentylfuran and n-hexanal in the control DWWN were2.9 and 2.3-fold than those in the ET-processed DWWN.In conclusion,ET significantly inhibited the lipid degradation of WWF and DWWN during storage.In addition,ET-160℃ had better inhibition effect.Finally,the effect of superheated steam combined with the control of key points in the process of making dry noodles on the lipid stability of DWWN was studied.The lipid degradation was severe in the process of making DWWN,the activities of lipase,LOX,POD,fatty acid value,the content of UFAs and tocopherols decreased by 35.7%,85.4%,44%,40.3%,40.6%and 82.7%,respectively,after WWF was made into DWWN.And the dough mixing had the greatest influence,the activities of lipase,LOX,POD,fatty acid value,the content of UFAs and total tocopherols in WWF decreased by 28.8%,76.7%,32.4%,32%,13.2%and 57.7%,respectively,and the total volatile compounds increased by 23.9%after dough mixing.It was found that superheated steam combined with vacuum mixing could significantly alleviate the degradation of UFAs,the reduction of tocopherols and tocotrienols and the formation of volatile compounds during storage.After 12 weeks of accelerated storage,UFAs and total tocopherols decreased by 2.7%and 10.9%,which were much lower than those of other groups(17.6%,46%).In a word,the lipid degradation of DWWN was severe during processing,but the lipid degradation of DWWN during storage was significantly alleviated by superheated steam combined with vacuum mixing.