Study On The Formation Kinetics And Prebiotics Effects In Vitro Of Lotus Seed Resistant Starch

Lotus seed starch is one of the richest carbohydrates in lotus seed.Amylose content of lotus seed starch is up to 40%,which makes lotus seed starch a good raw material for the preparation of resistant starch type3?RS3?.Our preliminary study found that there is a corresponding relationship between the structural characteristics of lotus seed resistant starch?LRS?and its prebiotics effect.However,the preparation of type 3resistant starch should undergoes retrogradation.Retrogradation is a complex process and influenced by many factors,which root in property of starch source,as well as environmental conditions for retrogradation.In that case,the structural characteristics and prebiotics effect of resistant starch change with the variation of retrogradation conditions.Therefore,it is particularly important to study the relationship between preparation environmental conditions,structural characteristics,and prebiotics effect of LRS.In this study,lotus seed starch was used for preparation of LRS,and the effects of three factors,namely water content,retrogradation time,and retrogradation temperature,on the structural characteristics and prebiotics effect of LRS were investigated.On this basis,water distribution model and Avrami equation were utilized for describing the relationships between influencing factors and structural characteristics,and the relationships between structural characteristics and probiotics effect were studied by Pearson correlation analysis.Results of the research are as follows:?1?Effect of water content on the structural characteristics of lotus seed resistant starch.Results of environment scanning electron microscope?ESEM?showed that LRS prepared at water content of 95%has more dispersed structure,while that prepared at water content of 50%had a denser structure with a porous surface.Intermediate-level water contents?70%and 80%?allowed a relatively long starch chain to re-associate and form resistant starch,which showed larger weight-average molecular weight?Mw?.In addition,results of X-ray diffraction test,solid-state NMR(¹³C CP/MAS NMR),fourier infrared spectroscopy?FTIR?showed that LRS prepared at intermediate-level water contents?70%and 80%?have higher total crystallinity,proportion of micro-crystalline region,proportion of double-helical structure,and degree of structural order than LRS prepared at low-level water contents?60%and 50%?and high-level water contents?95%and 90%?.Correlation analysis,which is based on the result of low-field nuclear magnetic resonance test?¹H NMR?,showed that proportion of bound water?measured by ¹H NMR?was consistent with the R_995/1022?measured by FTIR test?,and the proportion of channel water in B-type crystal?measured by ¹H NMR?was consistent with proportion of micro-crystal region?measured by XRD?.In that case,water distribution model was proposed to describe the corresponding relationship between the structural characteristics and moisture content of LRS.?2?Forming kinetics study of lotus seed resistant starch under the influence of temperature and duration.In this chapter,the structural characteristic of lotus seed resistant starch retrogradated at different temperatures?4,25,4/25??for different duration?0.5,1,2,4,8 days?were compared.The results showed that Mw,total crystallinity,proportion of double-helical structure,and degree of structural order of LRS increased with retrogradation duration at each temperature.All starch samples exhibited lamellar surface,while the structural characteristics of LRS prepared at different temperatures showed differences.Compared with LRS prepared in other temperatures,LRS retrogradated at 4? has relatively loose and finely divided morphological structure;LRS prepared at 4/25? has denser and uniformed morphological structure.Result of molecular weight of LRS showed that the LRS retrogradated at 4/25? had larger Mw.Meanwhile,result of XRD and solid-state NMR showed that LRS retrogradated at4/25? have higher total crystallinity and proportion of double-helical structure,and degree of structural order than LRS prepared at 4? and25?,whereas LRS prepared at 4? and 25? formed more perfect crystals than 4/25?.Kinetic study of Avrami equation fitting showed that retrogradation of lotus seed resistant starch at 4,25 and 4/25? were processes begin from instantaneous nucleation,while the rate of formation and diffusion of nucleus were different and followed the order:4?>4/25?>25?.?3?The prebiotic properties of structurally varied lotus seed resistant starchLRS prepared under different conditions were chosen as sole carbon resource of culture media for cultivate Bifidobacterium,Clostridium butyricum,mixed bacteria of Bifidobacterium and Clostridium butyricum,and fecal flora,and the proliferation and metabolism of bacteria in different culture media were compared.The results showed that most LRS with different structural characteristics could preferably promote the proliferation and metabolism of Bifidobacterium and Clostridium butyricum.Among all,LRS retrogradated at 25? for 1 and 8 days were the best carbohydrate that promoting the growth and acid production of Bifidobacterium and Clostridium butyricum.Bifidobacteria only produced lactic acid and acetic acid in culture medias added different carbohydrates respectively.Clostridium butyricum produced lactic acid,acetic acid,propionic acid and butyric acid in culture media added different carbohydrates respectively.The growth of mixed bacteria in culture media added different carbohydrates showed significant difference else.LRS retrogradated at 4/25? for 1 and 8 days had prominent promoting effect on the proliferation of mixed bacteria,while no significant promoting effect was observed in the acid production of mixed.The structure of fecal flora changed significantly after fermented in culture medias added different carbohydrates.Among them,the LRS prepared at 4/25? for 1 and 8 days showed abnormal flora structure,especially higher abundance of Proteobacteria and lower abundance of bacteroidetes.Compared with the functional analysis of flora,it was believed that LRS retrogradated at 4/25? for 1 and 8 days may preferred the growth of harmful bacteria.