Formation Mechanism And Physicochemical Properties Of Lotus Seed Amylose-fatty Acid Complexes Induced By Ultra-high Pressure Treatment

Recently,amylose-fatty acid complexes were defined as resistant starch type-5.Their anti-digestion effects are of particular importance for regulating postprandial blood glucose and promoting gastrointestinal health.In this paper,we present an innovative approach employing non-thermal treatment of ultra high pressure to prepare lotus seed amylose-fatty acid complexes.The effect of different fatty acids with distrinct chain length and degree of saturation on the physicochemical properties,multiscale structure(granular structure,aggregation structure,short range structure and molecular chain structure),thermal properties and anti-digestive properties of complexes were investigated.This study intends to explore the potential application of ultra high pressure in starch modification and further provide a theoretical basis for enhancing nutritive starch within staple foods.Main conclusions were displayed as follows:(1)Formation of lotus seed amylose-fatty acid complexes and their molecular propertiesThe self-prepared lotus seed amylose were employed to prepare complexes with fatty acids under different ultra high pressure treatments.Complex index,size distribution and molecular weight were obtained to analyze the basic properties of lotus seed amylose-fatty acid complexes.The results shows that the high pressure treated lotus seed amylose formed aggregations when contacted with water,while the formation of crystal complexes with fatty acids weakened this phenomenon.The molecular weight of lotus seed amylose declined with the pressure increased nevertheless the formation of complexes raised the value of Mw,Mn and polydispersity.The complex index of lotus seed amylose-fatty acid complexes were related to the chain length and degree of saturation of fatty acids,and decreased with the increase of processing pressure.(2)Structural properties of lotus seed amylose-fatty acid complexesWide-angle X-ray diffraction(WAXD)diffractograms indicated the presence of B-type polymorph within lotus seed amylose and both V6-type along with B-type polymorphs within complexes.The relative crystallinity enhanced since the formation of complexes and their value were related to the chain length,dispersity and degree of saturation of fatty acids.The result of nuclear magnetic resonance(NMR)further indicated the amylose-fatty acid single helix complexes were in V6?-type.Small-angle X-ray scattering(SAXS)and scanning electron microscopy showed that lamellar conformations were existed within both lotus seed amylose and lotus seed amylose-fatty acid complexes,and the crystal lamellae of complexes further packed as a framework of spherulites.Mass fractal dimension of lotus seed amylose increased due to the formation of lotus seed amylose-fatty acid complex.The free saturated fatty acids entrapped in amorphous lamellae can be detected by Fourier infrared spectroscopy,while the confocal laser scanning microscopy observed both entrapped saturated and entrapped unsaturated fatty acids.(3)Thermal properties of lotus seed amylose-fatty acid complexesThe thermal properties of lotus seed amylose-fatty acid complexes were discussed on the basis of their crystal structures.The result of differential scanning calorimetry(DSC)demonstrated that the complexes presented type I variation and the formation of complexes increased the onset temperature(To),peak temperature(Tp),conclusion temperature(Tc),and enthalpy change(?H).The melting temperature of lotus seed amylose-fatty acid complexes were in correlation with the chain length and degree of saturation of fatty acids.The mass-loss observed by thermogravimetric analyzer(TGA)appeared in both lotus seed amylose and lotus seed amylose-fatty acid complexes,nevertheless the loss rate of complexes were lower than that of amylose.The formation of lotus seed amylose-fatty acid complex decreased the solubility and swelling power of lotus seed amylose,which indicated the formation of thermal stable crystal structures.(4)Anti-digestibility of lotus seed amylose-fatty acid complexesThe in vitro digestion method established by Englyst were employed to evaluate the anti-digestibility of lotus seed amylose-fatty acid complexes.The formation of complexes increased the content of resistant starch(RS)and decreased the amount of rapid digestible starch(RDS)and slow digestible starch(SDS).The the chain length and degree of saturation of fatty acids affected the amount of resistant starch within complexes,in detail the RS content increased in the order of amylose-lauric acid>amylose-myristic acid>amylose-stearic acid among and amylose-oleic acid>amylose-linoleic acid>amylose-stearic acid.Besides,the rate of digestion of both lotus seed amylose and lotus seed amylose-fatty acid complexes were in the same digest pattern due to their helical structures.