Study On The Effects Of Persimmon Tannin On Starch Digestibility And Its Mechanism

Starch is a major source of carbohydrate for humans.The level of blood glucose is closely related to the digestion of starch.Persimmon tannin,which is a kind of polyphenol with high polymerization degree has important health-benefical effects such as: anti-oxidant,cholesterol lowering effect etc.However,there is limited information about its effects on starch digestion and glucose intake.Compared to proanthocyanidins from other fruits and vegetables,persimmon tannin has a unique structure with high polymerization degree and high galloylation,which may interact with starch digesting enzymes and starch strongly,thus inhibiting starch digestion and blood glucose forantion.This paper investigated the effect of persimmon tannin on the digestibility of low,intermediate and high amylose corn starch,and the interaction between persimmon tannin and the digestive enzyme which could provide theoretical foundation for the application of persimmon tannin as a functional food ingredients in starch food.The main results of this study were as follows:(1)The effect of persimmon tannin on starch digestibility and postprandial glycemic levelStarch digestion in vitro showed that,with the increase of amylose content,the enzymatic hydrolysis rate of starch increased gradually and the digestibility of three kinds of starch was inhibited after adding persimmon tannin.When the hydrolysis time was 120 min,15% persimmon tannin decreased the low amylose starch,intermediate amylose starch and high amylose starch hydrolysis rate by 22.64%,22.84%,32.24% compared to the control suggesting that the inhibitory effect of persimmon tannin on the digestibility of high amylose starch was better than that of low amylose starch.In vivo experiments,the blood glucose level of the rats fed with the persimmon tannin-starch paste was lower than that only fed the starch paste.The area under the blood glucose curve of three kinds of starch indicated that glucose curve area of the low amylose starch,intermediate amylose starch,high amylose starch added with 15% of persimmon tannin decreased by 6.61%,9.05%,11.33% respectively compared with the control group.It could be concluded that persimmon tannin could strongly inhibit the digestion of high amylose starch.Through the established of Caco-2 single cell model,we further found that 20?g/m L of persimmon tannin could effectively inhibit the absorption and transportation of glucose.(2)Interaction between persimmon tannin and starch digesting enzymeIn the Caco-2 cell model and in vitro starch digestion experiments,we found that persimmon tannin could effectively inhibited the activity of starch digesting enzymes.The inhibitory mode of persimmon tannin on alpha amylase and alpha glucosidase was competitive inhibition.The fluorescence spectra showed that the fluorescence intensity of alpha amylase and alpha glucosidase decreased with the increase of persimmon tannin.The fluorescence quenching mode of persimmon tannin on alpha amylase was mainly dynamic quenching,while the fluorescence quenching mode on alpha glucosidase was static quenching.The results of Fourier transform infrared spectroscopy showed that persimmon tannin could reduce the secondary structure content of alpha amylase and alpha glucosidase.These results primiarily indicated that the existing interaction between persimmon tannin and starch digesting enzyme.(3)Effects of persimmon tannin on physicochemical properties of starchThe effect of persimmon tannin on the physicochemical properities of three kinds of starch was explored by DSC,XRD and TA methods.The results showed that the gelatinization temperature,crystallinity and hardness of starch increased with the increase of amylose content.The gelatinization temperature,degree aging and gel strength of three kinds of starch were decreased when the persimmon tannin was added.The rheological properties of starch were different with different amylose content.After adding persimmon tannin,low amylose starch exhibits more viscous fluid properties,but the network structure of intermediate and high amylose gel system was strengthen.Persimmon tannin-starch showed similar infrared spectrum as that of starch and SEM analysis indicated that the structure of the three kinds of starch added with persimmon tannin was more porous than that without persimmon tannin.By studying the effects of persimmon tannin on the binding of starch and iodine,variation of starch size and changes of total phenolics content in persimmon tannin-starch complex,we found that persimmon tannin could combine with amylose and amylopectin,and it is stronger to bind to amylose than amylopectin.The interaction between these three kinds of starch and persimmon tannin could be through hydrogen bonds and hydrophobic interactions.