Morphologies And Gelatinization Behaviours Of High-amylose Maize Starches During Heat Treatment

Physicochemical properties and applications of cereal starch were influenced by amylose content and amylopectin structure.It is known that various physicochemical changes and phase-transitions during heat treatment of native starch were very complex and obscure.Although much work has been reported on the thermal properties of various starches,few reports have addressed the gelatinization behaviours of high-amylose maize starches under temperatures greater than 100°C.In this paper,the morphology,structure and gelatinization characteristics of high-amylose maize starches were investigated,with the objective of elucidating the heat treatment on granule morphologies and gelatinization behaviours of high-amylose maize starches involving granular swelling,native crystalline melting,loss of birefringence.Based on this study,the gelatinization process of high-amylose maize starch treated at above 100°C and in various glycerol concentrations can be comprehensively understand.The results of this study were showed as following:1.Native high-amylose maize starch granules display substantially heterogeneous shapes consisting of spherical granules,irregular granules and elongated granules with smooth surface.Maltese crosses at the center of the granules demonstrated that the high-amylose maize starches maintained a granular structure.The mean diameter of high-amylose maize starch granules were in 3~30?m,higher than those of normal corn starch.Gelatinization of the native high-amylose maize starches started began at115.3°C(T_o),peaked at 125.7°C(T_p),and completed at 130.7°C(T_c).The XRD patterns of the native high-amylose maize starches exhibited the peaks B-type diffraction at a 2?angle of approximately 17.3°,with a few smaller peaks at 2?angles of approximately 20.0°and 22.0°.2.High amylose maize starch granules also had hilum,located in the center of the round and oval starch granules.The central area of the granule was the most incompact region because this region was disrupted originally.The growth ring was observed in some starch granules,and it extends to the periphery from the hilum.3.The granules of high-amylose maize starches swelled slightly at 100°C,swelled remarkably at approximately 120°C and fully gelatinized at 140°C.The destruction of the starch structure began at the centre and expanded rapidly to the periphery.Small granules exhibited more resistance to being gelatinized.This higher resistance stems from the amylose double helices in the small granules requiring a higher temperature and energy input to dissociate completely than the shorter double helices in the large granules.4.The effects of glycerol on gelatinization behaviours of high-amylose maize starch at above 100°C were systematically evaluated through confocal laser scanning microscopy(CLSM)together with scanning electronic microscope(SEM)and differential scanning calorimetry(DSC).The textural analyses of high-amylose maize starch gels were carried out using a texture profile analyzer(TPA).The results prove that adding glycerol would promote the gelatinization of high-amylose maize starch,and the effect of glycerol concentration with 10%is superior than that of low concentration with 5%and high concentration with 20%and 50%on the promotion of starch gelatinization.This study is important to understand the granule morphologies and gelatinization behaviours of high-amylose maize starches for the purpose of application of them in supporting films and other field.