Effect Of Lactic Acid Bacteria Fermentation On Nutritional And Physicochemical Properties Of Coix Seed

Coix seed(Coix lachryma-jobi L.),an annual or perennial herb,has been widely cultivated in China and has long been considered as both a traditional Chinese medicine and a nourishing food.In this thesis,coix seed was selected as the research object.Firstly,the effect of Lactobacillus casei fermentation on the nutritional composition,biological activity and physicochemical property of defatted coix seed were studied.Then,the effect of fermentation with enzyme addition on the nutritional quality of defatted coix seed was investigated.Finally,the nutritional composition and biological activity of germinated coix seed during fermentation were discussed.This research would provide theoretical and technical support for the development and utilization of coix seed resources.1.Defatted coix seed was fermented by Lactobacillus casei,and the results showed that fermentation could significantly improve the nutritional value and biological activity of defatted coix seed.After fermentation,defatted coix seed protein was degraded,and a large number of peptides and amino acids were produced.The proportion of peptides with molecular weight less than 2000 Da gradually increased from 61.19% to 87.90% after fermentation.The content of total free amino acids also significantly increased,and it increased by 1.66 times after 48 h.Further,fermentation substantially augmented the antioxidant activity of both the water and methanol extracts of defatted coix seed.After fermentation,the total phenolic content,FRAP and ABTS free radical scavenging ability of water extract increased by 32.28%,26.67% and 25.00%,respectively,while those of methanol extract increased by 35.79%,24.14% and 34.78%,respectively.Moreover,the tyrosinase and xanthine oxidase inhibitory activities of defatted coix seed increased 13.01% and 21.42%,respectively,after 48 h fermentation.2.The effect of Lactobacillus casei fermentation on the physicochemical property of defatted coix seed was estimated.The results showed that the reducing sugar content of defatted coix seed increased firstly,then decreased.After fermentation,the p H gradually decreased from 7.1 to 3.7,while the titratable acid(TTA)gradually increased from 0.24 mg/m L to 3.62 mg/m L.The defatted coix seed with different fermentation time all showed typical A-type diffraction characteristics,but fermentation increased the relative crystallinity of the defatted coix seed flour.After 48 h fermentation,the relative crystallinity increased from 32.25% to 33.62%.SEM results indicated that fermentation reduced the interaction among starch,protein and other substances,and the compact structure of defatted coix seed became looser.Moreover,fermentation increased the peak,breakdown,final,and trough viscosities of defatted coix seed,while decreased the setback viscosity and the gelatinization temperature.3.Defatted coix seed was fermented by Lactobacillus casei with enzyme addition,and the results showed that fermentation with enzyme addition could further improve the nutritional quality of defatted coix seed.The TTA and reducing sugar content of defatted coix seed fermented with enzyme addition were higher than those of single fermentation.The degradation of defatted coix seed protein during fermentation was further promoted with enzymes addition.Compared to single fermentation,the contents of peptide and free amino acid of defatted coix seed fermented with enzyme addition were higher,and the proportion of peptides with molecular weight less than 500 Da increased.Further,fermentation with enzyme addition significantly increased the antioxidant activity of defatted coix seed.Total phenolic content,FRAP and the ABTS free radical scavenging of defatted coix seed fermented with enzyme addition increased by 52.12-226.83%,33.03-90.61% and 26.60-68.23%,respectively,compared to single fermentation.4.Coix seeds with different germination times were fermented by Lactobacillus casei,and the results showed that fermentation could further strengthen the nutritional and biological activities of germinated coix seed.During fermentation,the starch content of germinated coix seed gradually decreased,while the protein content remained stable.The reducing sugar content increased firstly,then decreased after fermentation.Meanwhile,the protein of germinated coix seed was degraded after fermentation,and both the proportion of small molecular of peptide and the content of free amino acid increased.Moreover,the total phenolic content,FRAP,ABTS free radical scavenging ability,tyrosinase and xanthine oxidase inhibitory activity of germinated coix seed gradually increased with fermentation time.