Research On Quality Analysis And In Vitro Gastrointestinal Digestion Characteristics Of Low-fat Soy Yogurt

The Low-Fat diet has gradually become the focus of people's attention.Low-Fat food can not only reduce the intake of calories,but also reduce the intake of excessive fat.Soy yogurt is a lactic acid fermentation product with a variety of nutrients and functional characteristics.However,there are few studies on Low-Fat soy yogurt,especially the effects of fat content and pH on texture,rheological properties and microstructure of soy yogurt.In this paper,soybean milk prepared with whole fat soybean powder and degreased soybean powder was used as the fermentation matrix,and the texture,rheological properties and microstructure of the fermentation products were compared by inoculation with lactobacillus plantarum B1-6.On the basis of previous studies,the effects of different fat contents and pH values on texture,rheological properties,microstructure and in vitro dynamic digestion of soy yogurt prepared with defatted soybean powder were compared.Finally,the texture and in vitro dynamic digestion of soybean yoghurt with different amounts of inulin and whey protein concentrate were studied.The main research results are as follows:1.With full-fat soy flour and the defatted soy flour as fermentation substrate preparation soy yogurt,it is found that low fat soy yogurt(SY-LF)in the same fermentation time than full-fat soy yogurt(SY-FF)higher acidity and lactic acid bacteria number of living bacterium,and higher hardness and elasticity,showed lower syneresis and has higher ability to hold moisture.By comparing the SY-LF and SY-FF gel behavior in the process of fermentation,SY-LF exhibited faster gel formation,gel time(energy storage modulus G'>1 pa)for 204 min,significantly below SY-FF gel time of 276 min,the gel pH of SY-LF(pH 5.49)less than SY-FF(pH 5.59),the combination of scanning electron microscopy(SEM)microstructure as a result,found in the SY-LF 8 h after fermentation protein gel microstructure more dense than SY-FF.Through principal component analysis,it was found that acidity,number of live lactic acid bacteria,texture and rheological properties were negatively correlated with terminal pH value.2.By comparing the texture,rheological properties and microstructure of soy yogurt with different fat contents,the effects of fat contents on the digestive characteristics of soy yogurt were compared by using the in vitro dynamic gastrointestinal digestion model.The results showed that with the increase of fat content(1%-5%)at the end of fermentation pH5.0 and 4.6,the number of viable lactic acid bacteria was in the range of 8.99-9.26 log CFU/mL,which was significantly higher than that of SY-LF 8.3-9.09 log CFU/mL(P<0.05)at corresponding pH.At the end of fermentation pH4.6,the soy yogurt with high fat content(3%-5%)reduced the hardness and increased the apparent viscosity.The results of oral chewing showed that both fat content and pH could affect chewing parameters and oil release rate.The chewing time of the samples with a harder texture were higher than those with a softer texture,among which SY-5.0(terminal pH)-2%(oil content)had the lowest chewing parameters due to its soft structure.The experimental results showed that with the increase of fat content,the adsorption amount of interfacial proteins increased gradually within the range of 1%-4%and reached the maximum adsorption value at 4%.When the adsorption value reached 5%,the adsorption amount of interfacial proteins began to decrease.The adsorption behavior of soybean protein affected the texture and microstructure characteristics of soybean yogurt.In vitro digestion results showed that the addition of soy oil could significantly affect the degradation of proteins and the release of peptides and free amino acids,among which the peptide content and free amino acid of S Y-4.6-4%were 3.11 mg/mL and 3473.77 mg/100g,respectively,which were 2.85 and 1.91 times of the peptide content and free amino acid of SY-4.6-LF.3.With inulin and whey protein concentrate(WPC)as the fat replacer added to soy yogurt,microbial results show that adding 1%-2%of inulin can significantly improve the titratable acidity,the acidity of SY-inulin(fat replacer)-2%(content)was 58°T,SY-inulin on the number of viable lactic acid bacteria in 8.73-8.95 log CFU/mL,higher than the number of viable lactic acid bacteria of SY-LF(8.39 log CFU/mL),When the inulin content was 1%,the water holding capacity reached the maximum(77.19%),and when it exceeded 1%,it would lead to excessive whey precipitation and poor texture.The texture results showed that when the inulin content was 1%,its hardness was similar to hardness of SY-LF.When the inulin content exceeded 2%,the hardness began to decrease and phase separation appeared.WPC also can improve the titratable acidity and the number of viable lactic acid bacteria.Among them,SY-WPC-4%had the highest acidity(60°T),and the number of viable lactic acid bacteria of SY-WPC was 8.48-9.12 log CFU/mL.When the WPC content was 2%-4%,the water holding capacity was higher than SY-LF.With the increase of WPC,the hardness of soy yogurt gradually increased,indicating that whey protein participated in the gel structure and formed a compact structure.According to SDS-PAGE results,inulin can make soybean protein more easily degraded during gastrointestinal digestion.The release of small peptide(<10 KDa)in gastric digestion stage is limited to a certain extent,but with the development of digestion time,the content of small peptide(<10 KDa)increases significantly under the combined action of pepsin and trypsin at the end of intestinal digestion(1-120).