| Soybean dietary fiber,the most abundant fiber in China,is mainly derived from the by-products of soybean processing.Due to the beany flavor,soybean dietary fiber is used as feed or fertilizer.At present,there are many methods to lighten the beany flavor in soy products,including enzymatic inactivation and fermentation,etc.However,the methods that can improve the flavor of dietary fiber are limited.Based on this fact,this study chose two soybean dietary fibers(okara,S-IDF)and their raw material-soybean meal as the research objects to explore the methods to improve the flavor of soybean dietary fiber based on edible fungi fermentation.Firstly,fermentation strains were selected,then the factors affecting flavor improvement and the application of dietary fiber after flavor modification in yogurt were explored.This study aimed to provide new strain selection and technical support for soybean dietary fiber flavor improvement.The main results are as follows:Combined with sensory evaluation,GC-MS and GC-O,the changes of flavor profiles and volatile compounds in soybean meal and two kinds of soybean dietary fiber before and after fermentation by four edible fungi(5.466 Tremella,5.528 Wolfiporia cocos,5.78 Wolfiporia cocos and 5.55 Wolfiporia cocos)were investigated.The results showed that the main beany volatile compounds in soybean meal,okara and S-IDF were as follows: Hexanal,trans-2-Hexenal,1-Octene-3-Ol,Decanal,and cis-6-Nonenal,etc.With a total relative content of more than 60%,these compounds caused the undesirable flavors of grassy,green and earthy smell.All of the 4 kinds of edible fungi have aroma-accompanying phenomena during fermentation.The beany flavor in each fermentation product all weakened,while the aromatic flavor such as floral and sweet generated.The results of GC-MS showed that the total relative content of beany flavor volatile compounds in the fermented product decreased.Among them,5.55 Wolfiporia cocos fermented okara decreased the most to 99.52%.Linalool,methyl phenylacetate,and phenethyl alcohol were produced by fermentation.Among them,the total relative content of aromatic flavor volatile compounds in 5.55 Wolfiporia cocos fermented okara was the most,which was 93.76%.This showed that the fermentation of edible fungi improved the flavor by reducing the content of beany flavor compounds,while generating volatile compounds with aromatic flavor.Among the four selected edible fungi,the 5.78 Wolfiporia cocos had the highest sensory acceptability and the best flavor improvement effect.A follow-up investigation was to investigate some of the biological characteristics of5.78 Wolfiporia cocos and inoculated it into three raw materials,and studied the effect of flavor improvement under different culture time.The growth curve,p H and volatile compounds of the fermentation broth were measured at the same time by collecting the fermentation broth of 5.78 Wolfiporia cocos in PDA medium for 3 d,5 d,7 d,and 9 d.The best cultivation time was 5 d?9 d,and the optimum growth p H was 3.0?5.0.The main volatile compounds in the fermentation broth were Linalool,Methyl Phenylacetate,Phenethyl Alcohol and 2-Undecone.With the extension of the cultivation time,the content of volatile compounds increased,and the flavor characteristics of flower aroma,tea aroma and sweet aroma continued to strengthen.The 5.78 Wolfiporia cocos were inoculated into 3 kinds of raw materials for fermentation.The results showed that in soybean meal fermented product,the total relative content of beany flavor volatile compounds in the 5 d product decreased the most from 70.01% to 12.89%,while the total relative content of aromatic flavor volatile compounds increased from 5.74% to 63.11% in the 7 d fermented product.In okara fermented product,the total relative content of beany flavor volatile compounds in the 9 d fermented product decreased the most from 77.33% to 14.88%,while the total relative content of aromatic flavor volatile compounds increased from 6.16% to 69.83% in the 9 d fermentation product.The total relative content of beany flavor volatile compounds in the 9 d fermented S-IDF products decreased the most from 60.14% to 21.53%,while the total relative content of aromatic flavor volatile compounds increased from 3.17% to 46.18% in the 7 d fermentation products.In summary,all the fermentation products had the best flavor profile and the highest sensory acceptability when the culture time was 7 d.Among them,linalool was the main aromatic volatile compound,which was the highest in the 7 d fermented okara product.Based on the sensory evaluation and the types of volatile compounds,the okara was used as a fermentation substrate for subsequent research.After adding additional glucose and amino acid,it was found that the additional glucose could speed up the growth of 5.78 Wolfiporia cocos to a certain extent.It had a positive effect when the addition amount was 0.5%,but it would cause a rapid decrease of p H when the addition amount was above 2.0%,hindering the normal growth of 5.78 Wolfiporia cocos.The additional phenylalanine could promote the synthesis of phenyl ethanol by 5.78 Wolfiporia cocos.When the dose was 0.1%,the content of phenyl ethanol was 27.56 ?g/L.The additional addition of glutamic acid could not cause the significant changes in volatile compounds.Solid-state fermentation was different from liquid-state fermentation.The decrease in moisture content made a large amount of mycelium cover the surface of the okara,resulting in a significant increase in the content of 1-octen-3-ol.By measuring the content of protein,dietary fiber and amino acid in the fermented product,the effect of 5.78 Wolfiporia cocos fermentation on the quality of okara was investigated.The results showed that with the extension of the fermentation time,the protein and dietary fiber content showed a trend of decreasing firstly and then increasing.The protein content was the lowest at 13.51% after 5 d fermentation.With the extension of fermentation time,the ratio of SDF and IDF in fermented okara tended to be balanced.At 7 d fermentation,IDF/SDF ratio reached 2.88.However,the content of all amino acids was below the taste threshold,which has little effect on the taste of the system.By adding flavor-improved okara into the flavored yogurt,the application of flavor-modified okara was studied.The results showed that when the added amount was 0.4%,both the stirred and solidified yogurt no longer had the beany flavor,and the taste improved compared with the original okara.The GC-MS results also confirmed the sensory evaluation results.In addition,typical volatile compounds in flavor-improved okara such as linalool and phenethyl alcohol were detected.All these results indicated that the method based on the flavor improvement of edible fungi can solve the problem of beany flavor. |
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