Preparation And Characterization Of Yam Resistant Dextrin By Acid Heating Method And Microwave Pretreatment-enzymolysis Method

Yam is a medicine and food homologous plant that can improve the function of the st omach and spleen.The comprehensive utilization of the by-products such as yam starch remaining after the extraction of the active ingredients is important.Resistant dextrin is a kind of water-soluble dietary fiber that can be added as a prebiotic to the food industry.It was studied that yam resistant dextrin was prepared from yam starch by acid-heating method and microwave pretreatment-enzymatic method.The physicochemical properties of the obtained YRD,including its stability,molecular weight,thermal and freeze-thaw stability characteristics as well as its digestibility and prebiotic effects were evaluated.In addition,the obtained YRD were further applied to investigating its effect on the formation of soy protein gel.The main results were as follows:(1)Preparation of yam resistant dextrin by acid-heating method:Yam starch was used as raw material to prepare yam resistant dextrin by acid-heating method.With resistance content and whiteness of the YRD as evaluating indicators,hydrochloric acid dosage,heating time,heating temperature and citric acid supplementation in the preparation process were optimized.The results showed that under the conditions of 0.11% hydrochloric acid addition,0.2% citric acid supplementation,150 heating temperature,℃1h heating time,the resistance content of YRD reached 48.07% with whiteness 48.38%.With the molecular weight about 6300 Da,the obtained YRD also exhibited excellent acid and thermal stability and contained α-1,2 glycosidic bond which was hard to be digested by in vivo enzymes.(2)Preparation of yam resistant dextrin by microwave pretreatment-enzymolysis method:Yam starch was used as raw material to prepare yam resistant dextrin by microwave pretreatment-enzymatic method.With the resistance content and DE value of the YRD as evaluating indicators,the microwave power and temperature,enzymolysis temperature,heating time,β-amylase and transglycosidase dosage,these technology parameters were explored for their influence on the preparation of YRD.The result showed that the optimal conditions were:starch pretreated by microwave with power of 60 W for 6 minutes,enzymolysis temperature of 75℃,heating time of 20 minutes,β-amylase addition of 20 U/g and transglycosidase addition of 35 U/g.Resistance content and solubility of the obtained YRD under the above conditions could be up to 40.33% and 47.01%,respectively.With a relatively low molecular weight of 4000 Da,it also displayed fairly good water solubility,thermal stability and high tolerance to artificial gastric and intestinal fluid.(3)In vitro Digestibility and prebiotic effect of yam resistant dextrin : The antidigestion ability of yam-resistant dextrin was determined by in vitro simulated artificial gastric / intestinal fluid,the results showed that: The prepared YRD by the two methods could be digested less than 1% after 240 min in artificial gastric fluid and less than 5% after 360 min in artificial intestinal fluid,exhibiting a strong antidigestion ability to both gastric and intestinal fluid;Further research focusing on YRD prebiotic effects were conducted through the study of yam resistant dextrin on the growth of intestinal probiotics and harmful bacteria.The results suggested that yam resistant dextrin had corresponding the most suitable concentration for each kind of intestinal probiotics,and a very obvious proliferation of the four tested intestinal probiotics was observed when the optimal amount was added.Yam resistant dextrin showed inhibition on intestinal harmful bacteria,Escherichia coli and Staphylococcus aureus.And the inhibitory effect enhanced gradually with increasing YRD concentration,however,the inhibitory effect was not as strong as fructooligosaccharides,the positive control of the experiment.(4)Applied characteristics of yam dextrin in soy protein gel formation: The effects of YRD addition(0%-1.0%,w / v)on the SPI gel formation were measured from aspects of its microstructure,rheological properties and secondary structure.The results showed that gel properties of soy protein gels could be significantly enhanced by YRD supplementation in a concentration-dependent manner.Compared with YRD-free SPI gel,SPI gel containing 1%(w / v)YRD exhibited a 11.4 times elevation of gel strength and a 27.87% increase of water retention,respectively.According to the SEM and FTIR analysis,the enhancement of YRD-induced SPI gel properties may be attributed to the formation of a stable three-dimensional gel network with reduced free sulfhydryl groups and altered protein structure,suggesting that YRD may be a good gel modifier.