Effect Of Premma Microphylla Turcz Addition On Physicochemicl And Digestive Characteristics Of Probiotic Tofu

Premna microphylla turczs(PMTL)wildly distributed in China and has high edible,economic,and medicinal value.Due to the rich of pectin and flavonoidsin PMTL,it has been received increasingly attention,but most of the researches focuse on the extraction and production of pectin.Moreover,fermentation is regarded as an acceptable and reliable food technological method to improve sensory qualities and health benefits of the final product.In order to satisfy consumers’ pursuit of high nutritional value and high sensory attributes food,PMTL was added in probiotic tofu to improve the texture,sensory qualities,functional and digestive characteristics of probiotic tofu.The results were expected to provide theoretical guidance for the development of functional foods with PMTL added.Moreover,this study also has certain reference meanings to available utilisation and development of the wild resource of PMTL.PMTL as a potential low-methoxyl pectin sources to make soy protein-based products.Hence,the effect of PMTL on tofu qualities such as textural characteristics,rheological properties,water distribution,sensory attributes were investigated to determine the optimal amount of PMTL addition.Three antioxidant indexes were used to evaluate the antioxidant activities of probiotic tofu added with PMTL and the total phenol content,total flavonoid content,and 6 main phenolic compounds were also determined.Since the change of texture may affect the digestive characteristics of probiotic tofu with PMTL added,the changes of protein degradation and bioacceptability of proteins were investigated by determing the particle size,hydrolysis degree and other indexes in the process of digestion.This study consists of three parts.The main results are as follows:1.Effect of PMTL addition on physicochemical properties of probiotic tofuThe addition of PMTL can promote the growth of lactobacillus plantarum in probiotic tofu,and the number of live bacteria increases with the addition amount of PMTL(0.4-1.6%,w/w).The results of water holding capacity and texture profile analysis showed that the hardness,gumminess and chewiness of probiotic tofu were significantly improved while the PMTL addition amount was 0.4%and 0.8%(w/w).The values reached maximum at 0.8%(w/w),which were 1.49 times,1.44 times,and 1.43 times of plain probiotic tofu,respectively.However,when the added amount increased to 1.6%(w/w),the water holding capacity,adhesiveness and chewability all significantly decreased.Moreover,PMTL addition improves the rheological properties of probiotic tofu,significantly increase G’value at the end of fermentation,and present a certain dose-dependent relationship.When the added amount is 1.6%(w/w),the value of G’ at the end of fermentation was increased by about 4.23 times compared with the plain probiotic tofu.T2 relaxation time distribution curves were found variously in tofu samples supplied with different PMTL concentration.The relaxation time of water exhibited a significantly decrease with increasing PMTL concentration,which implied the reduction of water protons mobility in tofu samples.The addition of PMTL had a significant effect on the color of probiotic tofu.With the increase of the addition amount,the color of probiotic tofu was darker(L*value significantly decreased,a*value and b*value significantly increased).The results of sensory evaluation showed that the probiotic tofu with an additive amount of 0.8%(w/w)PMTL was the most acceptable,with highest scores for appearance and taste,an appropriate herbal flavor and low beany flavor.2.Effects of fermentation and the addition of PMTL on the antioxidant activity of probiotic tofuLactobacillus plantarum fermentation and the addition of PMTL to probiotic tofu could both significantly improve the DPPH free radical scavenging activity(DPPH),reducing power(RP)and ferric reducing antioxidant power(FRAP)of soy milk and probiotic tofu,respectively with a dose-dependent relationship.The values of DPPH,RP and FRAP of probiotic tofu with PMTL added were the highest.The EC50 values of the DPPH and RP of the probiotic with PMTL added are 3.39 mg/mL and 34.24 mg/mL.Lactobacillus plantarum fermentation increased the content of total phenols and total flavones in soybean milk and promoted the conversion of glucoside isoflavones to aglycones isoflavones.The addition of PMTL in probiotic tofu increased the content of total phenols,total flavones and aglycones isoflavones in probiotic tofu by 1.20 times,1.65 times and 1.10 times respectively.Principal component analysis showed that the contents of total aglycones isoflavones,genistein,total flavones,total phenols,DPPH,RP and FRAP had good correlation,which indicated that aglycones isoflavones,genistein,flavones and phenols had strong antioxidant capacity,aglycones isoflavones had stronger antioxidant activities than glucoside isoflavones.3.Effects of addition of PMTL on the digestive characteristics of probiotic tofuAddition of PMTL in probiotic tofu can significantly reduce the particle size of probiotic tofu before and during the digestion.During intestinal digestion,the degree of hydrolysis of probiotic tofu added with tofu wood was always the largest among the three samples,indicating that adding tofu wood to probiotic tofu could promote the hydrolysis of soybean protein during digestion.During intestinal digestion,the degree of hydrolysis of probiotic tofu with PMTL added were always the highest among the three samples,indicating that adding PMTL to probiotic tofu could promote the hydrolysis of soybean protein during digestion.SDS-PAGE results showed that the probiotic tofu with PMTL added had more bands before fermentation and in stomach digestion.During intestinal digestion,large molecular weight proteins which could not enter lanes were both observed at the top of electrophoresis gel of probiotic tofu and probiotic tofu with PMTL added.Smaller particle size is beneficial to the reaction of food matrix and digestive enzymes in the gastrointestinal tract.Combined with the high degree of hydrolysis of the sample,it can be concluded that the probiotic tofu with PMTL added is easier to be digested by the human body than the plain probiotic tofu.The addition of PMTL has no significant effect on the soluble protein content of probiotic tofu in the gastric digestion stage,while the soluble protein content of probiotic tofu increased significantly in the intestinal digestion stage due to the addition of PMTL.The content of small peptides(<10 kDa)of probiotic tofu supplemented with PMTL was significantly higher than that of probiotic tofu during the whole digestion process.It can be concluded that the addition of PMTL in probiotic tofu had a positive effect on improving the bioacceptability of probiotic tofu.