The Property Study Of High Hydrostatic Pressure Treated Buckwheat Starches And Their Effect On Mice Gut Microbiota

Starch is the second largest naturally synthesized high-molecular material.It is not only cheap but also can be isolated from millions of resources.However,due to being water insoluble,poor heating resistant performance,and easily retrogradated,native starches need to be modified by artificial methods to extend its processing characteristics and applications.Buckwheat(Fagopyrum esculentum Moench)is an unique dual-use crop of food and medicine around the world.Common buckwheat and tartary buckwheat are the two main cultivated varieties whose health benefits have been reported in many Chinese traditional medicine books.Because of having many pharmaco1 logical activities,including antioxidant,anti-inflammation,anti-diabetes,hypolipidemic and anti-tumor,buckwheat has recently caught more and more concerns from researchers.Buckwheat starch,which has a lot of special physicochemical properties,has higher amylose and resistant starch(RS)contents compared with rice,wheat and other starches,and this is not only benefit for controlling the postprandial blood glucose level,but also meaningful to prevent and regulate oxidative stress and chronic inflammation response.However,there has not found the variety of buckwheat with extremely high amylose and RS contents,so we need a safe way to modify the structure and physicochemical properites of buckwheat starch to further increase amylose and RS levels and enhance its functionality.Chemical modification is the widely applied,most productive and important method for various starches.However the chemicals will increase the safety risks of the food,therefore the study of physically modified starches has been become the research hotspot.As a nonthermal processing technique,high hydrostatics pressure(HHP)treatment,which can meet the consumers’ requirements for natural,nutritional and healthy foods,is the alternative technique to thermal processing technique.HHP treatment has already been applied to modify various starches,but there are few studies on the buckwheat starch domestically.The present research applied HHP technology to modify the common and tartary buckwheat starches incorporated the SEM,RVA,DSC,XRD,in vitro digestibility,PCR,and highthroughput sequencing technologies to investigate the effect of different HHP pressures on physicochemical,gelatinization and retrogradation,rheology,and textural properties of both common and tartary buckwheat starches.It also analyzed and tested the changes in hydrolysis rate,rapid digestible starch(RDS),slowly digestible starch(SDS),and RS contents,and preliminarily studied the molecular mechanism of HHP-modified buckwheat starches ameliorating insulin resistant and adjusting the intestinal microbiota of rat.These results will provide a theoretical basis for the application of HHP-modified buckwheat starches in the prevention and treatment of metabolic syndrome as well as adjustment of intestinal microbiota.The main results of this study are as follows:1)HHP treatment did not significantly change the moisture,total starch,protein,crude lipid,and ash contents of buckwheat starch,while notably increased the amylose content(AMC),which was positively correlated to the pressure level.The AMC in HHP-600 sample of both starches had the highest increase with 7.3% and 5.1%,respectively.2)HHP treatment markedly increased the granule size and average diameter of buckwheat starch and the ratio of large granules,and it also broke the crystalline structure and decreased the relative crystallinity.At 120~360 MPa,the morphology of buckwheat starches was not obviously altered.After treated at 480 MPa,the starches’ granules collapsed and got together,showing the buckwheat starches began to gelatinize.There may be a critical pressure value between 360 MPa and 480 MPa which can result in the gelatinization of buckwheat starch.At 600 MPa,most of the starch granules had deformed to become a gel-like appearance,and the A-type crystalline pattern was transferred to B-type pattern.3)HHP treatment significantly increased the swelling power and solubility of common and tartary buckwheat starches at 50~60 °C,while opposite trends were found at 70~90 °C.Compared with native starch,light transmittance,freeze-thaw ability,the hardness,adhesiveness and resilience of modified starch pastes significantly decreased and the agglomeration tendency progressively increased,which showed the HHP treatment limited the granule swelling during the gelatinization resulting in the increase in the retrogradation rate.4)The degree of gelatinization of buckwheat starch significantly increased with the HHP level increasing,while the gelatinization temperatures and enthalpy notably decreased.These showed HHP treatment broke the crystalline and double helix structures in buckwheat starch,decreasing the required energy for the gelatinization.The HHP treatment also limited the hydration and swelling of buckwheat starch,resulting in the decrease in viscosity of buckwheat gels and the increase in its thermal stability during heating processing.Allbuckwheat starches belong to non-Newton fluid and the rheological curves could be fitted by Herschel-Bulkley model.Under the same shear rate,the apparent viscosity of buckwheat starch was positively related to the HHP level,showing the shear thinning phenomenon.5)The in vitro hydrolysis of native tartary buckwheat was lower than native common buckwheat.HHP treatment decreased the hydrolysis and RDS content of the two starches,while increased the SDS and RS levels.Therefore,the HHP-modified buckwheat starch having more healthy potential than native starch could be used in buckwheat functional food production.6)HHP-modified buckwheat starch decreased the level of oxidative stress induced by high fat diet in mice,regulated the fat metabolism,changed the serum lipid constituents,lowered the degree of the liver damage and limited the obesity.These changes were positively related with RS content.The high fat diet significantly decreased the variety of gut microbiota in mice and the intake of HHP-modified buckwheat starch increased the variety and amount of beneficial bacterium,which was probably related to the decrease of oxidative stress and obesity in CBM and TBM groups’ mice.However,the relationship between gut microbiota structure and obesity should be further studied.The results in this study showed the significant effect of HHP treatment on the properties of two kinds of buckwheat starches.HHP-modified buckwheat starch had significant down regulation function of the oxidative stress and obesity conditions in mice feed by high fat diet.Furthermore,it also could notably alter the structure of gut microbiota,increasing the beneficial bacterium.This study provided the theoretical basis for the further application of buckwheat starch and new evidence of nutritional and functional properties of HHP-modified buckwheat starch.