| Okara is by-product produced in the process of producing bean products.Okara is rich in dietary fiber,protein,free amino acids,vitamins and minerals.Because of its higher water content,roughness and strong beany smell,only a few of them are used as feed.Besides,okara is easy to rot,which leads to most of them being discarded,resulting in waste of resources and environmental pollution.To sum up,it is necessary to make better resource utilization of okara and turn waste into treasure.The fishy taste and rough feeling of okara can be overcome by fermentation such as edible fungus fermentation rich in a variety of enzymes,and yeast fermentation can give it a strong flavor of fermentation.at the same time,fermentation can also hydrolyze its rich proteins into peptides and amino acids that are easier to absorb.And the roughness can be overcome by further enzymatic hydrolysis.Considering that noodles are one of the staple foods of Chinese people,but there are few highly nutritious noodles,fermented okara rich in protein peptides and soluble dietary fiber can be used as one of the raw materials of noodles,which can greatly improve the nutritional value and flavor of noodles.Therefore,in this paper,Pleurotus ostreatus and Saccharomyces cerevisiae were used as fermentation bacteria to study the changes of nutritional components and physiologically active substances in okara during fermentation.Then the fermented okara were hydrolyzed by enzymatic hydrolysis,and the optimum enzymatic hydrolysis conditions were determined.Then the changes of nutritional composition and functional characteristics of noodle samples with different amount of okara were studied,and the best addition amount of okara in noodles was determined.（1）Taking soluble protein,polysaccharide content and mycelium growth as indicators,Gaofeng 246 was selected as the fermentation strain.Taking crude polysaccharide and amino acid nitrogen as indexes,the optimum fermentation conditions of Gaofeng 246 fermented okara were determined as follows:inoculation amount 7.4%,fermentation time 7 d,fermentation temperature 27.5℃and sucrose addition 0.26%.During the fermentation of bean dregs by Pleurotus ostreatus,the radical scavenging rates of 2,2-diphenyl-1-picrylhydrazyl radicals（DPPH）and 2,2-azinobis（3-ethylbenzothialozinesulfonic acid）（ABTS）increased to 97.94%and 28.74%respectively on the 7th day,and the absorbance of reducing power increased significantly from 0.23 to 1.35.The free sulfhydryl group reached a peak value of 5.54μmol/g on the 5th day,which was 44.98%higher than that on the 0th day.The content of crude polysaccharide increased significantly with the increase of fermentation time,and reached the highest at the end of fermentation,which was 6.07%.Under the optimum conditions,the free amino acid content,soluble dietary fiber content and protein content of fermented bean dregs were 1491.1 mg/100g,5.67 g/100g and 23.28%,respectively.To sum up,the nutritional components and antioxidant activity of okara were improved by Pleurotus ostreatus fermentation.The trend of Fourier transform infrared spectroscopy of okara before and after fermentation is almost the same,only the intensity of absorption peak is slightly different,which shows that fermentation has not changed the structure of bean dregs.（2）After the fermentation of Pleurotus ostreatus,Saccharomyces cerevisiae was added to continue the co-fermentation.Compared with the okara of 0 h,the soluble protein reached the maximum value at the fermentation time of 48 h,which increased by 1.9 times.The content of crude polysaccharide reached the maximum at 24 h,which increased by 8.87%.The contents of total phenol and free sulfhydryl reached the maximum at 36 h,which increased by 54.11%and 12.96%respectively.Fermentation improved the flavor of bean dregs,especially the types and contents of aldehydes and esters changed significantly.After fermentation,although the content of aldehydes did not decrease,the content of aldehydes with beany smell,such as hexanal,decreased significantly,and the content of aldehydes with fruit flower fragrance,such as phenylacetaldehyde,increased.The ester content of okara fermented by Pleurotus ostreatus and Saccharomyces cerevisiae increased obviously,and the threshold of ester compounds was low,which made great contribution to the aroma and flavor of okara.With the contents of soluble dietary fiber（SDF）and insoluble dietary fiber（IDF）as indicators,the optimum conditions for hydrolyzing fermented okara by cellulase were as follows:enzymolysis time 2 h,p H 4,enzymolysis temperature 45℃and enzyme addition 3.5%.Under these conditions,the SDF content of bean dregs is 16.8%,which is 8.75 times,2.96 times and 2.1 times higher than that of unfermented okara,okara fermented by Pleurotus ostreatus and okara fermented by Pleurotus ostreatus yeast respectively.The infrared spectra of control okara,co-fermented okara and okara treated by co-fermentation and enzymolysis all have typical absorption peaks of cellulose polysaccharides,but only some bands and absorption peak intensities are different,indicating that most functional groups and group structures in okara have not been changed by fermentation and enzymolysis.After fermentation and enzymolysis,the absorption peak at 1250 cm-1 was weakened,indicating that fermentation and cellulase hydrolyzed some cellulose and lignin in okara dietary fiber.（3）The okara fermented by Pleurotus ostreatus and Saccharomyces cerevisiae supplemented by enzymolysis were added to flour to make noodles,and the effects of different okara addition on noodle quality were studied.The results showed that with the increase of dosage,the cooking loss rate of okara noodle decreased,with the lowest loss rate of 4.65%at 35%,and the highest comprehensive sensory evaluation of noodles was 21.27.With the increase of dosage,the contents of SDF and IDF in noodles increased significantly.When the dosage was 40%,the contents of SDF and IDF in noodles were the highest,which were 1.67%and 12.70%respectively.SDF was 6 times and 1.5 times higher than that in noodles without okara.In vitro starch digestion experiments were carried out on noodle samples with different addition amounts.It was found that the rapid digestible starch content（RDS）in noodles with okara decreased（63.79%～49.82%）,while the slowly digestible starch（SDS）increased from 20.99%to25.45%,and the resistant starch（RS）increased from 5.62%to 13.58%.Compared with the reference food white bread,the starch hydrolysis rate of noodles with 0%～40%bean dregs decreased,and reached the lowest at 40%,which was 38.83%.With the increase of the dosage,the hydrolysis index and predicted glycemic index（p GI）of noodles showed a downward trend.When the addition was 35%and 40%,the p GI was 69.16and 65.13 respectively,which changed the noodles from high（glycemic index）GI food to medium GI food.The protein amide I region of noodls was studied.The results showed that when the addition was 40%,theα-helix andβ-sheet in noodles were 16.79%and 33.52%,respectively,which indicated that its structure was more orderly and protein polymerization was stronger.According to the cooking characteristics and sensory score of noodles,the final addition amount of okara was determined to be 35%. |
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