Study on physicochemical properties and flavor changes of different protein components during fermentation of soybean yogurt
Soybean yogurt is a new plant-based yogurt with healthy nutrition.In this study,soybean whey,7S and 11S protein compo-nents were isolated and purified from soybean by salting-out isoelectric point precipitation method.The dynamic changes of pH value,acid-ity,lactic acid bacteria proliferation,protein hydrolysis degree,and particle size of different components during fermentation were investi-gated,as well as the differences in rheological properties,microstructure,volatile compounds,and sensory characteristics of fermentation products,to clarify the contribution of different protein components to the texture and flavor formation of soybean yogurt.Results showed that with the increase of fermentation time,the pH value of 11S protein fermentation products decreased significantly(P＜0.05),and the acidity,the lactic acid bacteria number,the protein hydrolysis degree,and the average particle size increased significantly(P＜0.05).At the same time,the rheological results showed that the 11S protein fermentation products had the highest viscosity,and the microstruc-ture showed rough granular and more compact and uniform protein aggregation.In addition,GC-MS and electronic nose results confirmed that 7S protein could produce a large number of yogurt aroma compounds such as 2-hexanone,2-octanone,2-nonanone,2,3-butanedione,2,3-pentanedione,and acetoin after fermentation,while 11S protein produced more beany flavor compounds such as hexanal,pentanal,(E)-2-heptenal,(E)-2-hexenal,1-hexanol,1-pentanol,1-octen-3-ol,benzaldehyde,acetic acid,and 2-pentylfuran,with low sensory acceptance.Results showed that 11S protein was the key component of the yogurt texture formation,and it was also the main component of the interaction with beany flavor compounds.This study would provide a theoretical reference for the quality optimization and flavor im-provement of soybean yogurt products.
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