| Sweet potato with high development and utilization values is one of the most importantcrops in our country. Its quality depends on the properties of sweet potato starch. Theamylose content of sweet potato starch affects the physicochemical properties. In study ofstarch/hydrocolloid mixtures, the amylose content plays a significant role in the synergisticeffect between starch and hydrocolloid. Therefore, this research aimed to investigate theeffect of amylose content on the structure of sweet potato starch and physicochemicalproperties of sweet potato starch/hydrocolloid mixtures. Besides, correspondingphysicochemical properties were employed to evaluate the starch films attributed by theaddition of hydrocolloid. Researches were conducted as follows:Firstly, the differences in chain structure of sweet potato starch with different amylosecontent (waxy (WSP), normal (NSP) and high amylose sweet potato starch (HSP), amylosecontent of1.75%,20.33%and41.33%, w/w, respectively) were compared. The resultsindicated that the weight-average molecular mass of starch molecule of NSP was highest,while that of HSP was lowest. The mean square radius of HSP was biggest while that ofWSP was smallest. The polydispersity index and chain length of WSP was biggest andlongest, while that of NSP and HSP were similar. The external chain length of NSP waslongest while that of HSP was shortest. The inner chain length of HSP was longest whilethat of WSP was shortest. Amylopectin of NSP had the maximum content of A chainsegment, while HSP had the maximum content of B chain segment. NSP and HSP werecompact globular structure except WSP in solvent DMSO.Secondly, WSP, NSP and HSP were mixed with guar gum (GG) to study the effects ofamylose content on physicochemical properties of the mixture systems. The results showedthat WSP/GG system was biphasic with the gum located in the continuous phase. Phaseseparation led to the increase of peak viscosity, yield stress, consistency coefficient and thedecrease of dynamic modulus (G’ and G’’) of the mixtures. And due to without of amylosecontent, the synergistic effect between starch and gum was not obvious. For HSP, theinteractions between amylose and GG via hydrogen bonding inhibited the aggregation ofamylose. Therefore, the three-dimensional network structure of the gel system wasenhanced and the retrogradation of starch was inhibited. The interactions between GG andamylose were more obvious when starches contained more amylose. The SEM of allsamples showed that the addition of GG enhanced the order of three kinds of starch/gummixtures.B1, B2segment content and external chain length of amylopectin influenced the steady flow properties of starch/GG mixtures significantly. The chain length of amylopectinsignificantly affected the gel strength of mixtures. And the molecular weight distributionaffected the syneresis of mixtures significantly. Thus, amylopectin with shorter chain length,longer external chain length and more B1, B2segment content was easily combined withGG.Finally, the different mixing ratios of guar gum were applied to waxy, normal and highamylose sweet potato starch films. The results showed that the tensile strength of themixture films increased with the increasing gum concentration. And the similar trendfavored the amylose content. The tensile strength of NSP/GG mixtures film was greaterthan HSP film, when the mixing ratio was40:1and20:1. Interaction between amylose andGG via hydrogen bonding improved the tensile strength of mixture films. The addition ofGG reduced the elongation at break. But there is no obvious regularity between changes andGG content. |
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