Effects On Nutrition And Bio-functionality Of Okara By Solid-state Fermentation With Actinomucor Elegans DCY-1

Soybean is one of the most important legumes and oil crops in world.The popularity of consumption of soy derived foods,such as soymilk and tofu has led to generation of the soymilk residues.Soymilk residues is a group of insoluble byproducts deriving from the production of soybean curd(tofu),soymilk and other soybean products.Except for a small part using for animal feed,the rest are discarded as industrial garbage.To solve this problem,the solid-state fermentation(SSF)technology can be applied in food industrial production.SSF is not only environmentally friendly,but can enhance the nutritional value and functional properties of cereal gains.Fermented soybean residues,also named Meitauza,is a traditional Chinese food with a long history.Fermented soybean residues in the form of a small family factory production,so the lack of standardized production process,uncertainty of fermentation microorganisms and uncontrolled fermentation conditions.In this paper,a food-grade fungal strain DCY-1 was isolated from Chinese traditional fermented soymilk residues and identified as Actinomucor elegans.The novel strain was used to solid-state fermentation(SSF)of okara for improving the functional properties and encourage their utilization in the formulation of value-added functional foods.Followed are the main research contents and results:1.Isolation and identification of fungal strain DYC-1 and the determination of soybean residues fermentationThe strain DCY-1 was isolated and screened from the Chinese fermented soymilk residues.The morphology observation and molecular identification indicated that the strain was Actinomucor elegans.Using Actinomucor elegans DCY-1 to prepared soybean residues and taking the sensory evaluation and ammonium nitrogen content as the standard,the three factors of initial moisture of okara,temperature and time of fermentation were carried on the single factor expriment.The optimum condition were determined:70%moisture content of okara were homogeneously inoculated with 1%(v/w)A.elegans DYC-1 spore starter and culturing 60 h at 25 °C.2.Effects on the chemical and nutritional characteristics of okara by solid-state fermentation with Actinomucor elegans DCY-1According to the best fermentation conditions,the contents of nutritional components were analyzed,and the results indicated that the quality was enhanced after the fermentation.The total crude protein?fat and soluble fiber increased from 28.14%to 30.61%,12.05%to 13.32%and 6.01%to 11.71%,respectively.Besides the okara protein amino acid composition has changed,and improve the basic nutritional value of soymilk residues.The change of pH,total acidity,reducing sugar content and glycoamylase activity were also monitored during the fermentation.During the SSF,the pH increased while fermentation process,just a slight downward in the early moments of the experiment.During the fermentation with Actinomucor elegans DCY-1,the content of reducing sugar increased from 7.63 mg/10 g to 44.36 mg/10 g and the value of glycoamylase activity was 2789.52 U/g at 60 h.3.Effects on protein degradation and the ACE-inhibitory activity of okara by solid-state fermentation with Actinomucor elegans DCY-1Protein pofiles of okara isolates were monitored by sodium dodecyl sulfate polyacrylamide-gel electrophoresis(SDS-PAGE)and reverse phase high-performance liquid chromatography(RP-HPLC)indicated that okara proteins were degraded into peptides during fermentation.Degree of hydrolysis(DH),content of soluble protein and protease activity were also investigated.During the fermentation with Actinomucor elegans DCY-1,the value of DH and soluble protein content increased from 1.28%to 15.10%and 7.17 mg/g to 11.54 mg/g,respectively.The protease activity also increased to 1319.33 U/g at 60 h.In addition,peptide contents of molecular weight cut-off at 10 kDa also increasing,increased from 27.72 to 115.57 mg L-glu-tathione/g dry matter.SSF okara also showed a significantly higher angiotensin I-converting enzyme(ACE)inhibitory activity(61.17%)at the end of fermentation and the contents of peptide were highly correlated with ACE inhibitory activity(r=0.945).4.Effects on the total phenolic content and in vitro antioxidant activity of okara by solid-state fermentation with with Actinomucor elegans DCY-1The total phenolic content(TPC)of okara gradually increased during fermentation,the highest value was 2.07 mg GAE/g dry matter at 48 h.SSF okara showed high antioxidant activities,which included ferric reducing antioxidant power,reducing power,ferrous ion chelating activity and scavenging effect of 2,2-diphenyl-1-picrylhydrazyl(DPPH),2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt(ABTS)and hydroxyl radicals.Compared to the control,the antioxidant activities mentioned above increased by 2.54,2.36,2.67,3.00,4.03 and 4.38-fold,respectively.The contents of total phenolic contents were highly correlated with FRAP(r = 0.966),reducing power(r = 0.850),ferrous ion chelating activity(r = 0.891),DPPH radicals scavenging activity(r=0.803),ABTS radicals scavenging activity(r=0.885)and hydroxyl radicals scavenging activity(r = 793).