Study On The Digestibility Of Rice Starch Subjected To High Pressure Homogenization And Fatty Acid Complex

Rice starch,a main ingredient in human diet,is mostly rapid digestible starch（RDS）which will produce high blood sugar response after absorption,and increase the risk of chronic metabolic diseases such as diabetes and obesity.Considering the trend of modern nutritious healthy diet and the importance of starch digestibility in trophic function,a method combined with high-pressure homogenization（HPH）and fatty acids was used to regulate the digestibility of rice starch in this study.Based on a systematic study of the effects of HPH on the multi-scale structure and digestibility of rice starch,HPH was then used to prepare rice starch-fatty acid complex and the relationship between multi-scale structure and digestibility of complex was further revealed.The results could provide theoretical basis for the application of HPH in food production with specific digestibility.During HPH,on the one hand,the molecular chains of rice starch was broken by the shearing force,resulting the decrease of the average molecular weight,mean square radius of rotation andα-1,6 ratio,and the increase of amylose content.Meanwhile,the hydrogen bonding mode,helix structure and ordered structure were disrupted,transforming into the amorphous structure.On the other hand,the molecular chains with higher degree of freedom in amorphous state were rearranged by hydrogen bond interaction,and the new single helix structure,double helix structure and ordered structure were formed.It could help shield the action site of amylase in starch molecule,resulting in a decrease in rapidly digestible starch（RDS）content and an increase in resistant starch（RS）content in rice starch.Low circles with high pressure,or high circles with low pressure are beneficial to the orderly arrangement of molecular chains of rice starch and promote the formation of RS.When the homogenization condition was 150MPa×1,the ordering degree of rice starch molecule was the highest,and its anti-digestion performance was also the highest.Rice starch-saturated fatty acid complex was prepared by HPH under 150MPa×1.The structure and digestibility of complex were studied with modern analytical techniques.The results showed that the increasing amount of saturated fatty acid led to an increase of complex index,short-range ordered degree,single helix content,the relative crystallinity and the ordered structure of complex,and the amorphous structure gradually turned to a structure in which the crystal and the amorphous lamella were staggered.Moreover,with the same addition,the saturated fatty acids with longer carbon chain decreased the complex index,but increased the short-range ordered degree,the single helix content and the relative crystallinity.In addition,the helix structure changed from V₇ to V₆ while crystalline structure transformed from typeⅡ_b to typeⅡ_a.The increase of molecular arrangement degree and the decrease of amorphous structure content intended to form an alternative permutation by ordered and amorphous lamella.Those changes finally revealed that the increase of the addition amount and carbon chain length of saturated fatty acid could decrease the RDS content and promote the formation of slowly digestible starch（SDS）and RS content in rice starch.Furthermore,the rice starch-unsaturated fatty acid complex was prepared by HPH and the effects of different kinds of unsaturated fatty acid and its addition on the structure and digestibility of complex were discussed.The results showed that the rice starch-unsaturated fatty acid complex was mainly composed of typeⅡ_a structure.With the increase of addition,the changing trend in complex index and multi-scale structure of unsaturated fatty acid complex is consistent with that of saturated fatty acid complex.With the same addition,the unsaturated fatty acids complex with longer carbon chain decreased the complex index and amorphous structure content,but increased the short-range ordered degree,single helix content,relative crystallinity and ordered structure.In addition,compared with cis-monounsaturated fatty acid complex,trans-monounsaturated fatty acids complex had higher complex index,degree of short-range structure,single helix content,relative crystallinity and ordered structure.Besides,the complex index,single helix content and relative crystallinity of polyunsaturated fatty acid complex were the lowest while its short-range ordering degree,double helix content and ordered structure content were the highest,resulting to a more homologous alternative arrangement of ordered and amorphous lamella.These structural alternations eventually increased the content of SDS and RS in rice starch,and the trend became more obvious with the increase of the content of unsaturated fatty acids.The anti-digestibility order of complexes:saturated fatty acid>polyunsaturated fatty acid>trans-monounsaturated fatty acid>cis-monounsaturated fatty acid.After clarifying the changes of multi-structure and digestibility of rice starch induced by HPH and fatty acid with different structures（chain length,cis-trans and unsaturation）and additive levels,Pearson correlation analysis was used to reveal the key factors regulat ing the digestibility of rice starch.The related physical models were further established,revealing the relationship among HPH conditions,structure and addition of fatty acids,multi-structure and digestibility of rice starch-fatty acids complexes at molecular level,which provided a theoretical basis for the development of new starch-based nutritional health foods.