Effects Of Exogenous Starch On Quality And Digestive Tract Metabolic Performance Of Konjac Tofu

Konjac tofu was a thermo-irreversible gel product formed by the removal of acetyl groups from konjac glucomannan（KGM）under alkaline heating conditions.As a low-calorie satiety healthy food,it had a broad market.However,konjac tofu was prone to dehydration and shrinkage,which reduced the appearance quality and could be stored for a short time.It affect the commerciality of the product.In addition,the konjac tofu made from high-purity KGM had a hard texture when heated,which affected the palatability of the product.Therefore,in order to improve the appearance and edible quality of konjac tofu,producers added starch when making konjac tofu.The high caloric value of starch might reduce the health value of konjac tofu.In this article,the texture profile analysis（TPA）index and water holding capacity of konjac tofu were used as evaluation indicators.The production formula of pure konjac tofu was optimized by a random combination test of two factors.Based on this,the amount of KGM was adjusted,and starch was added.Orthogonal experiments were performed to select optimized formulas that added corn starch（CS）,plantain starch（CKS）,and potato starch（PS）when making konjac tofu.Through rapid visco analyzer（RVA）,rheology,and scanning electron microscope（SEM）,the mechanism of the effect of starch on the quality of konjac tofu was explored.The microstructure,hardness change and flavor of konjac tofu containing three kinds of starch were compared with pure konjac tofu to study the addition of starch effect on the quality of konjac tofu.And in vitro simulation of human oral,stomach,small intestine digestion and cecal fermentation in mice was conducted to explore the effect of starch on konjac tofu.The effect of digestive performance and cecal fermentation performance reflected the effect of starch on the health value of konjac tofu.In addition,through the color reaction between iodine-potassium iodide and starch,a method for quantitative detection of added starch in konjac tofu was established by spectrophotometry.The main conclusions of the study are as follows:（1）Pure konjac tofu production formula:2.0%KGM（w/w）,Ca（OH）₂ was added at 3%of KGM usage;corn konjac tofu production formula:1.4%KGM（w/w）,CS addition amount was 300%of KGM usage,Ca（OH）₂ was added at 3%of KGM usage;canna edulis ker konjac tofu formula:1.7%KGM（w/w）,CKS addition was 50%of KGM usage,Ca（OH）₂ was added at 3%of KGM usage;potato konjac tofu formula:1.7%KGM（w/w）,PS addition amount was 50%of KGM use amount,Ca（OH）₂ was added at3%of KGM usage.The TPA indexes and water holding capacity of the prepared konjac tofu were better than those of commercial konjac tofu samples 1 and 3.The TPA indexes and water holding capacity of corn konjac tofu were much better than those of pure konjac tofu,canna edulis ker konjac tofu and potato konjac tofu.were slightly better than pure konjac tofu.（2）Using RVA to prepare KGM solutions with a concentration of 1.4%and 1.7%.During the swelling of KGM in water,the viscosity of the solution continues to rise,without peak viscosity and valley viscosity,that is,the maximum value of KGM water absorption and swelling was not reached within 13 minutes of the gelatinization procedure.When CS,CKS and PS were added at 100%,50%,and 50%of the amount of KGM used,the gelatinization characteristics of KGM dominated the gelatinization characteristics of the mixed system,and the system still had no peak viscosity and valley viscosity during gelatinization.But as the amount of starch added increased,the gelatinization characteristics of the system were getting closer to the gelatinization characteristics of the added starch.The added starch particles will compete with KGM for water molecules in the mixed system.Among them,PS had the strongest ability to compete with water molecules,which seriously hindered the swelling process of KGM,while CS had the weakest ability to compete with water molecules.（3）During the steady shearing process,as the amount of starch added increased,the determination coefficient R² of the Power-Law model fitting increased.When the amount of CS was 300%of the amount of KGM,and the amount of CKS and PS was50%of the amount of KGM,n was the smallest and K was the largest.It was consistent with the optimized formula selected in the orthogonal test.In dynamic rheology,the G’value of all systems was always greater than G’’,which had good gel characteristics.With the increased of frequency,G’and G’’in all systems increased,the amount of CS added increased,and the system G’increased;the amount of CKS and PS increased,the system G’decreased.G’’had the same trend with G’as the amount of starch added.（4）The microstructure of pure konjac tofu was a messy honeycomb,and starch konjac tofu had a flaky network.As the temperature rose,the hardness of all types of konjac tofu increased,the hardness of pure konjac tofu increased rapidly,and the addition of starch slowed the rate of increase of konjac tofu hardness.The oil absorption rate and salt content of starch konjac tofu were higher than those of pure konjac tofu,which has stronger flavor.（5）Pure konjac tofu has no digestible sugar production in the mouth,stomach,and small intestine,and the konjac tofu mixed with starch could be partially hydrolyzed in the mouth and not hydrolyzed in the stomach,most of the hydrolysis can be completed within 20 min.But compared with pure starch,The rapidly digestible starch（RDS）content of starch incorporated into konjac tofu decreased,slowly digestible starch（SDS）content increased,and resistant starch（RS）content did not change significantly（P>0.05）.It shows that deacetylated konjac glucomannan（D-KGM）can delay starch digestion,but can not prevent starch digestion.In the process of cecal fermentation,the ability of konjac tofu with starch to lower pH is higher than that of pure konjac tofu,but the short chain fatty acid and lactic acid bacteria content produced by fermentation for24 h by the former are less than the latter.It is indicated that eating konjac tofu with starch will rapidly raise blood sugar and reduce the intestinal probiotic effect of konjac tofu.（6）A method for detecting whether starch was added to konjac tofu was established.Scanned in the 400¹000 nm wavelength with a spectrophotometer,the scanning spectrum of the konjac tofu without starch in the 400¹000 nm wavelength has no obvious peak.The maximum absorbance wavelength of konjac tofu with different starch was 595⁶05 nm,and the maximum absorbance value had a linear relationship with the starch concentration in the solution.Established a linear equation for regression of starch absorbance at 600nm on starch content after starch konjac tofu solution developed color by iodine-potassium iodide solution.The equation was used to detect the amount of starch incorporated in konjac tofu.This method has good reproducibility when the solution absorbance is 0.232⁰.653.