Effects Of Physical Modification On Physicochemical Properties And Starch Digestibility Of Chinese Yam Flour

In this paper,the effects of physical modification on physicochemical properties and starch digestibility of Chinese yam flour were studied.First,the raw/cooked yam flours were prepared by vacuum drying,freeze vacuum drying and spray drying to study their rheological properties,gelatinization properties and digestion properties.The results showed that raw yam flour reflected a higher pasting temperature,and the freeze-dried cooked yam flour had higher peak viscosity.All yam flours showed non-Newtonian fluid characteristics,and the viscoelasticity of frozen cooked yam flour was the highest.Among three drying methods,freeze vacuum drying was more suitable for drying the yam flour needed in the follow-up research.Based on the determination of drying method,the raw material of yam flour was obtained,the yam flour was modified by heat-moisture treatment(HMT),autoclaving treatment(AT)and annealing(ANN)to investigate the effects of different hydrothermal treatments on the physicochemical properties and in vitro starch digestibility of yam flour.The thermal stability of yam flour modified by HMT distinctly improved.An obvious inhibition of in vitro starch digestibility was found in yam flour modified by HMT,with the resistant starch(RS)content increasing by13.41%.The crystalline pattern of all modified yam flours was still A-type,and the crystallinity was increased compared with that before modification.Hydrothermal treatments made the protein in yam flour agglomerate and adhere to starch granules,and the effect of HMT was the strongest.CLSM showed that the starch being coated or embedded by protein was the principal cause for the differences in the digestibilities of modified samples.In order to further improve the modification effect and increase the RS content of the sample,the combined-hydrothermal treatments were performed on the yam flour.The results showed that the RS content of the four groups of combined-hydrothermal treated samples is as follows: AT-HMT > HMT-AT > ANN-HMT > HMT-ANN.The combination of HMT and AT is more likely to improve the stability of the sample and promote the formation of recrystallization.The change of crystallinity of the combined-hydrothermal treated samples is consistent with the change of RS content.At the same time,this paper also made a preliminary exploration on how the yam protein(YP)affects the properties of the yam starch(YS)in the system.Under thecondition of physical mixing,there are hydrogen bond and electrostatic complexation between YS and YP.The presence of YP affected the physical accessibility of amylase,resulting in decreased RDS content and increased SDS and RS content.With the increase of YP,the thermal stability,pasting viscosity and pasting temperature increased,and the swelling ability of yam starch was inhibited.Finally,yam starch-yam protein blend was treated by HMT to study the change of physicochemical properties and starch digestibility.The results showed that adding yam protein to yam starch before HMT significantly improved the thermal stability of the samples.With the increase of yam protein content,the crystallinity of the blends increased first and then decreased.The addition of yam protein further reduced the in vitro starch digestibility,which significantly reduced the RDS and SDS content and increased the RS content of the sample.