Study On Improving The Instant Properties And Digestibility Of Kudzu Powder By Complexing With Fatty Acids

Kudzu powder is a popular functional food because of the presence of active ingredients,such as isoflavones.Kudzu powder has poor instant properties,and it is easy to agglomerate when directly prepared with hot water,so it must be prepared with cold water first.The conventional method improves the dispersibility and water absorption of kudzu powder by adding a large amount of sucrose,maltodextrin and other auxiliary materials to inhibit agglomeration.However,this method reduces the purity and edible quality of kudzu powder,hinders the development of kudzu powder industry.Previous studies had shown that starch could form V-type complexes with a small amount of fatty acid,thereby inhibiting the swelling and gelatinization rate of starch.It is speculated that the formation of starch-fatty acid complexes may reduce the gelatinization rate of kudzu powder,so the kudzu powder can not quickly form a gel network when directly brewed with hot water,thereby avoiding agglomeration which was caused by the encapsulation of raw particles with gel.Therefore,this paper aims to improve the instant properties of kudzu powder by forming starch-fatty acid complexes,and studied the effects of drying methods,fatty acid chain length and complex temperature on the instant properties of complexed kudzu powder.The main results were as follows:In this study,the drying method of complexed kudzu powder was optimized first.The complexed kudzu powder was obtained by kudzu powder mixed with fatty acid after co-gelatinizing and drying.The drying method had an impact on the instant properties of complexed kudzu powder.Compared with oven drying and far-infrared drying,the complexed kudzu powder prepared by spray drying and freeze-drying had lower bulk density,more uneven particle surface and amorphous structures,which made them had stronger water absorption capacity,thereby improved the instant properties.After the complexed kudzu powder prepared by spray drying and freeze drying were directly dispersing with hot water,the agglomeration rates were 6.0%and4.6%,and the consistency coefficients were 16.67 and 13.60 Pa·s~n,which were significantly better than that of oven drying and far-infrared drying.This indicated that the best preparation methods of complexed kudzu powder were spray drying and freeze drying.Then,the effect of fatty acid chain length on the instant properties of complexed kudzu powder was investigated.The spray drying method that could be commercialized and produced continuously was used to complex the kudzu powder with different chain length fatty acids.Lauric acid(C12),myristic acid(C14),palmitic acid(C16)and stearic acid(C18)could all be complexed with kudzu powder to form V-type complexes,the complexing index were 90.41%,75.35%,70.22%and 49.76%,respectively.The agglomeration rates of the obtained fatty acid complexed kudzu powder were 6.04%,0.08%,0.18%and 22.20%,which were significantly lower than the original kudzu powder(42.31%).C14 and C16 had the best effective in reducing the agglomeration rate of kudzu powder.CLSM analysis further demonstrated that the V-type complexes were formed on the surface of the kudzu particles.DSC and RVA analyses showed that the thermal stability of kudzu powder was significantly increased(peak pasting temperature from 81.40 to 103.70℃)and the onset pasting time was prolonged(from 375 to 511 s)after complexing with C14 or C16.As a result,the time for water to enter the interior of the complexed kudzu powder to generate viscosity was prolonged,which enabling the complexed kudzu powder to be fully dispersed and absorbed sufficient water for pasting,thereby reducing the agglomeration rate.Finally,the complexed kudzu powder with the lowest agglomeration rate was selected for the study,and the effect of complexed temperature(75,85 and 95℃)on the instant properties and digestibility of the complexed kudzu powder was further investigated.The complexed kudzu powder at three temperatures showed A+V,V and V crystalline with peak pasting temperatures of 84.9+100.9,102.9 and 103.7℃,respectively.The onset pasting times were 500,476 and 520 s,respectively.These results indicated that the thermal stability was improved and onset pasting time was prolonged when the kudzu powder complexed with C14 at 75℃.Compared with the original kudzu powder,the agglomeration rate of the three complexed kduzu powders decreased by 42.21%,38.86%and 42.23%,respectively;The consistency coefficient was increased by 16.73,9.76 and 2.60 Pa·s~n,respectively.These results indicated that the instant properties of the complexed kudzu powder prepared at 75℃were better than those at 85 and 95℃.Compared with the complexing temperature of 85 and 95℃,FTIR and SEM showed that the proportion of components with amorphous structure and molecular weight below 1.0×10~7g/mol was lower when the complexing temperature was 75℃,which could explain why the best instant properties of the complexed kudzu powder with fatty acids was achieved at 75℃.In addition,the optimal conditions(spray drying,myristic acid and complexing temperature of 75℃)were used to prepare complexed kudzu powder,and its digestibility was studied.Compared with original kudzu powder,its resistant starch content was significantly increased by 4.76%.In this paper,the instant properties and digestibility of kudzu powder were significantly improved by complexing with fatty acid.This research provided a new insight for the development of instant starch-based products.