Effect Of Germination On Physiological Activity Of Soymilk Fermented By Lactic Acid Bacteria And Quality Of Soy-based Yoghurt

During soybean germination,the endogenous enzyme system was activated,the storage substances including protein and fat were decomposed into small molecular substances such as free amino and free fatty acids which were more suitable for human absorption,along with the increase of physiologically active components and the decrease of antinutrients.Germinated soybean is a raw material of plant protein different from soybean sprouts which were used only as vegetables.This topic studied the influence of germinated soybean components,fermentation performance and physiological activity of soymilk fermented by lactic acid bacteria while investigated the effect of germination on the off-flavor components of soymilk.Based on the above research,the germinated soybean with appropriate bud length was selected to prepare yoghurt.The research results will provide a basis for the deep processing of germinated soybean and the improvement of the quality of soy-based yoghurt.Firstly,the effects of germination on various components of soybean and the fermentation performance of soymilk fermented by lactic acid bacteria were investigated.The results showed that within 72 h of germination time,the bud length of soybean was 12 cm;glycinin andβ-conglycinin degraded obviously while the contents of trichloroacetic acid soluble nitrogen and total free amino acid increased by 3.76 and 2.23 times respectively.In addition,the contents of soybean oligosaccharides,trypsin inhibitor and phytic acid decreased in varying degrees.Soymilk prepared from germinated soybean with different bud length was fermented by lactic acid bacteria,the time to reach the fermentation end point（p H 4.5）decreased from 7.2 h to 5 h while the titratable acidity increased from 42.18°T to 66.56°T.The hardness and consistency of fermented soymilk decreased with the extension of bud length,and the gel strength also decreased.The number of viable lactic acid bacteria by germinated soybean with bud length of 12 cm increased by 5.17 times.Then,the effects of germination on the physiological activity of soybean and soymilk fermented by lactic acid bacteria was investigated.Within 0～12 cm of bud length,the contents ofγ-aminobutyric acid,isoflavones in soymilk fermented by lactic acid bacteria increased by 5.30 and 1.15 times respectively,the total phenols content reached 108.59μg GAE/g,and the vitamin B₁₂ content increased significantly（P<0.05）.The in vitro antioxidant capacity of germinated soybean and soymilk fermented by lactic acid bacteria increased with the extension of soybean bud length.The ACE inhibition rate of fermented soymilk was 1.46times higher than ungerminated soybean fermented by lactic acid bacteria when the bud length was 12 cm.Through gas chromatography-mass spectrometry analysis,it was found that with the increase of bud length,the content of off-flavor in soymilk prepared by germinated soybean increased significantly（P<0.05）.The content of off-flavor can be reduced by the treatment of germinated soybean with bud length of 9 cm,.The germinated soybean with 4 cm bud length and the treated germinated soybean with 9 cm bud length were fermented under the same conditions after pulping,on the basis of comprehensive consideration of flavor,physiological activity and input-output,it was determined that the germinated soy-based yoghurt with bud length of 4 cm was used as the raw material to prepare the germinated soy-based yoghurt.The effects of six different direct-throwing starters on the flavor components,texture properties and sensory evaluation were compared to further improve the quality of germinated soy-based yoghurt.The sensory evaluation and overall acceptance of germinated soy-based yoghurt prepared by starter A was the highest.Then,the effects of carbon and nitrogen sources on the fermentation characteristics and flavor of germinated soy-based yoghurt were investigated.It was found that with the addition of sucrose,glucose and soybean peptides,the fermentation acid production rate was improved while its acidity was reach above 70°T.Finally,the technological process of preparing germinated soy-based yoghurt with soybean as raw material was put forward on the basis of the above research.Through the above process,the acidity,texture characteristics and physiological active ingredients of soy-based yoghurt were significantly improved.