Improvement On Quality Of High-fiber Tofu And Its Mechanism

Manufacturing process of soybean products may produce a large number of wet okara,which can cause resources wasting and environmental pollution.In this study,high-fiber tofu was manufactured by high-pressure homogenization and microbial transglutaminase(TGase),and the improving mechanism of high fiber tofu quality was further studied.Firstly,the effects of homogenization pressure,okara contents,TGase concentration,and incubation time on the quality of high-fiber tofu were studied.Secondly,the optimal production process of high-fiber tofu was obtained by establishing a multiple regression model,and the nutritional components of high-fiber tofu were analyzed.Finally,the improving mechanism of high fiber tofu quality by TGase was studied in terms of the microstructure,rheological properties,intermolecular force,and protein molecular structure.The main conclusions are as follows:(1)High-pressure homogenization significantly reduced the particle size of high-fiber soymilk.At the pressure of 40 MPa,the D50 of high-fiber soymilk was reduced from 238μm to 36 μm,while the content of okara had no significant effect on it.Homogenization pressure had no significant effect on the gel strength and water holding capacity of high-fiber tofu.The gel strength of tofu did not changed significantly when the content of okara was more than 25%.In addition,there was a positive correlation between okara content and water holding capacity.When the content of okara was 100%,the water holding capacity of tofu increased from 0.54 to 0.79.Sensory evaluation experiments showed that high-fiber tofu resembled similar score in color and flavor compared with common tofu,while the score was lower in terms of taste and overall acceptability compared to traditional tofu,and the content of okara was negatively correlated with overall acceptability of high-fiber tofu.(2)TGase significantly increased the gel strength and improved the quality of high-fiber tofu.The gel strength of high-fiber tofu increased first and then decreased with the enhanced TGase concentration.Gel strength increased with the prolonged incubation time,under the conditions of TGase concentration of 0.15%and incubation at 50℃ for 2 h,the strength of high-fiber tofu increased from 50.54 g to 79.13 g.The water holding capacity of high-fiber tofu increased gradually with the increment of TGase concentration,while incubation time had no significant effect on it.Sensory evaluation experiments showed that TGase had no significant effect on the score of color and flavor,but it could increase the score of taste of high-fiber tofu.When incorporated with 0.15%(w/w)TGase,50%okara and incubated at 50℃ for 2 h,the sensory score of high-fiber tofu was 1.26 times of traditional tofu.(3)TGase offset the negative effect on the quality of high fiber tofu by okara.Multiple linear regression analysis showed that high fiber tofu possessed the best quality under the conditions of 0.15%(w/w)TGase,60%okara and incubation for 4 h.Nutritional quality analysis showed that the content of protein,fat,and ash of high-fiber tofu decreased by 8.12%,10.28%,and 18.49%,respectively,while the starch,dietary fiber,and soy isoflavone content increased by 204.93%,90.62%,and 22.22%,respectively.(4)Under the optimal process,the gel strength of high-fiber tofu increased from 54.23 g to 115.9 g.TGase induced the formation of uniform and dense gel network and significantly increased the modulus of high-fiber tofu.During the formation of tofu,hydrophobic interactions and disulfide bonds played an important role,ionic bonds and hydrogen bonds also participated in the formation of tofu.After adding TGase,ε-(γ-glutamine Acyl)lysine formation were induced,while the relative comtribution of hydrophobic interactions and disulfide bonds were significantly decreased.Changes in protein structure showed that free sulfhydryl content increased,a-helix and random coil contents decreased,while β-sheet and β-turn angle contents increased,and 7S,11S fractions polymerized into aggregates with the heating treatment With the presence of TGase,a large number of ε-(γ-glutamine Acyl)lysine were formed between the soybean proteins,which resulted in the formation of insoluble protein aggregates,and strengthened the gel network and enhanced the gel properties of high-fiber tofu.