Study On The Inhibition Of Lipid Rancidity In Oat Dried Noodles And Black Soybean Noodles

Coarse grain dried noodles(CGN)are rich in dietary fiber,polyphenols,vitamins and minerals,etc.,which cannot meet the needs of consumers for staple foods,but also meet their pursuit of nutritional health.However,the lipid of CGN is easily rancidity which caused by high content of polyunsaturated fatty acid and lipid-degradation enzymes,thereby influencing its nutritional value and safety.This article firstly studied the effects of superheated steam(SST)and extrusion treatment(ET)on the lipid storage stability of oat dried noodles(ODN)and black soybean noodles(BSN).Secondly,the method of extrusion combined with skimming and packaging improved was used to further regulate the lipid storage stability of ODN and BSN.Firstly,the effects of the two heat treatments on the endogenous enzymes,fatty acid and tocopherols in the raw oats and black soybeans was studied.The results showed that SST at160°C for 10 s,the lipoxygenase(LOX),lipase and peroxidase(POD)activities in oats were completely inhibited.After SST-190°C for 40 s,the activity of LOX,lipase,and POD in black soybeans decreased by 40.5%,94.5% and 99.9%,respectively.At the same time,the total fatty acid content of oats and black soybeans increased significantly(p < 0.05)after SST.The total tocopherol content of the oats treated with SST increased significantly(p < 0.05).However,the content of tocopherol in black soybeans was significantly(p < 0.05)reduced after SST.Extrusion treatment(ET)at 90°C reduced 100% of lipase activity in oats and black soybeans.When the temperature of ET exceeds 110°C,the POD activity of oats and black soybeans cannot be detected at all,but the activity of LOX in oats and black soybeans was only reduced by 36.0% and 98.1%,respectively.In addition,the contents of total fatty acid and tocopherol in oats and black soybeans are significantly(p < 0.05)reduced after ET at110°C and 130°C.Secondly,the effects of SST on the lipid rancidity of ODN and BSN during storage was studied.The results showed that the activities of lipase and POD in the ODN and BSN after SST were significantly(p < 0.05)reduced,the activity of LOX in the BSN was significantly lower than that of control group and decreased significantly during storage,but the LOX activity in the oat noodles after SST was significantly higher than that of control group during the early storage period,then decreased significantly after 6 weeks.The free fatty acid(FFA)value of ODN and BSN with SST-190°C was reduced by 94.4% and 16.7% respectively.And the FFA value of the ODN in SST groups did not change significantly during storage,while the FFA value of the BSN showed a downward trend.During storage,the degradation degree of total fatty acid of ODN and BSN in the SST-190°C group was the lowest,which were12.3% and 23.0%,respectively,and the stability of tocopherol in the 190°C-treated ODN and BSN were significantly(p < 0.05)increased.Moreover,SST effectively inhibited the production of acids and furans in the ODN during storage,and the content of aldehydes,acids and furans in the BSN was also significantly reduced.Thirdly,the effects of ET on lipid rancidity during storage of ODN and BSN were studied.The results showed that the enzyme activities of the ODN and BSN after ET at 130°C were significantly(p < 0.05)decreased.The FFA values of ODN and BSN in the ET-110°C and 130 °C groups were significantly lower than those of the control group,and showed a downward trend during storage.The total fatty acid in the BSN was reduced by 20.6% during storage,but ET with 110°C and 130°C accelerated the fatty acid degradation of the ODN,which was 17.3% and 19.5%,respectively.The total tocopherol content of the ODN with ET decreased firstly and then increased during storage,while the degradation degree of tocopherol content in the BSN was significantly(p < 0.05)lower than that of the control group.In addition,the content of volatile flavor compounds in the ODN increased significantly after ET,while the content of volatile compounds in the BSN were significantly reduced during storage.Fourthly,the effects of defatting-extrusion treatment(DET)on the lipid rancidity in the ODN(ET-90°C)and BSN(ET-130°C)during storage was studied.Studies have shown that the FFA value of defatted-extruded dried noodles was significantly lower than that of the non-defatted group(p < 0.05).During storage,the FFA values of ODN and BSN in the ET group decreased rapidly within 2 weeks and then increased.While the FFA value of ODN with DET did not change significantly after 2 weeks,and the changes of BSN with DET was as same as that of the ET group.The fatty acid composition of non-defatted noodles had no significant changes(p > 0.05)after 8 weeks of storage.The total fatty acids of ODN and BSN after DET were degraded by 11.2% and 8.7%,respectively.However,the consumption of polyphenols and the content of volatile compounds in the ODN and BSN with DET was markedly reduced during storage.Finally,the effects of packaging(PE,deoxidizer,and aluminum foil)on lipid rancidity in the ODN and BSN during storage were studied.Studies have shown that the FFA values of the ODN and BSN in the deoxidized package and aluminum foil package were higher than the PE group,and the changes of FFA value was the same as that of the PE group during storage.Deoxidized packaging and aluminum foil packaging had a certain effect of inhibition on the degradation of polyphenols in the ODN and BSN during early storage period.In particular,deoxidized packaging could effectively improve the stability of free polyphenols in BSN.In addition,deoxidized packaging could also effectively inhibit the release of volatile flavor compounds in the ODN and BSN,and delayed the lipid oxidation reaction.