Mechanism Governing Rice Glutelin Fibril Aggregates On Inhibition Of In Vitro Wheat Starch Digestion

Rice is one of the important food crops in China.The protein content of rice is about 8-13%;rice protein has high biological valence and digestibility,hypoallergenicity,antioxidant properties,blood pressure lowering,anti-cancer and other important functions.However,the insoluble rice protein in neutral solution and can not form a gel network structure limit its application in food.The previous research of the research group found that the rice gluten fibril aggregates(RGFAs)made from rice glutelin(RG)can significantly reduce the in vitro digestibility of starch,but the mechanism has not been clarified.In order to elucidate the inhibition mechanism of RGFAs on starch digestibility,this project deeply investigates the effects of RGFAs on starch in vitro digestibility,starch molecular structure,and starch hydrolase activity.The main findings and conclusions are as follows:(1)The addition of RGFAs(2 h,6 h and 10 h-RGFAs)significantly reduced the in vitro digestibility of starch.The hydrolysis rate of starch digestion decreased from 98.7±3.0%(pure starch)to 86.8±3.0%(6 h-RGFAs),and the content of rapid digested starch decreased from 65.2 ± 2.0%(pure starch)to 37.5 ± 1.3%(6 h-RGFAs).The inhibition rate of RGFAs to α-amylase and glucuronidase activity was 39±2.7%(2 h-RGFAs),and 37.8 ± 4%(10 h-RGFAs),and the inhibition rate of bi-enzymatic activity was 39.5±0.1%(2 h-RGFAs),significantly higher than the activity inhibition rate of mi gluten to mono-enzymes(17.7±3.2%and 25.7 ± 10.9%)and bi-enzymes(23.6 ±1.5%)(p<0.05).From the picture of SEM,it can be observed that wheat starch will adhere to RGFAs,and during the heating process,the samples that added RGFAs appear to have the form of starch particles ruptured but unable to form a network structure,thus affecting the formation of the starch gel structure.(2)RGFAs affected the gelatinization process,thermodynamic properties,and crystal structure of starch.RGFAs inhibited the gelatinization of wheat starch,and the peak viscosity of wheat starch gelatinization in the hybrid system decreased from 1625.7 ± 10.6 cP of pure starch to 1041 ± 11.3 cP to 1157.5±34.6 cP(p<0.05);through infrared spectral scanning and X-ray diffraction,it was found that 2 h-RGFAs led to starch short-range structure order from 0.73 ± 0.01(pure starch)to 0.86 ± 0.01(p<0.05),while 6 h and 10 h-RGFAs reduce the short-range structural order of starch to 0.68±0.01 and 0.58 ±0.01(p<0.05);RGFAs lead to an increase in the relative crystallinity of starch,from 2.04 ± 0.1%of pure starch to 8.75 ±0.2%to 14.35 ±0.2%(p<0.05),indicating that the presence of RGFAs leads to a more dense starch crystal structure.(3)RGFAs of different structures exhibit inhibition mechanisms that are not exactly the same for amylase activity.By changing the RGFAs concentrations(2.8,8.4,14,19.6,and 28 mg/mL)and substrate concentrations,using the Lineweaver-Buck double reciprocal curve analysis,it was found that 6 h and 10 h-RGFAs promoted an increase in the Michael’s constant(Km)of α-amylase,showing competitive inhibition,and 2 h-RGFAs exhibited anti-competitive inhibition of α-amylase activity.All three RGFAs exhibited mixed partial competitive inhibition of amylose glycosidase activity.Thus,by comparing the structure of 2 h-RGFAs with 6 h and 10 h-RGFAs and the difference in inhibition effect on starch digestibility and amylase activity,the inhibition mechanism of RGFAs on starch digestibility is manifested as:on the one hand,RGFAs achieve embedding of starch due to its rigidity and extreme length-to-width ratio,and the hydrogen bond,electrostatic and hydrophobic interaction between RGFAs and starch is enhanced by its increase in surface functional groups,limiting the contact between starch and its hydrolases;on the other hand,Protein-protein interactions between RGFAs and amylase increased,inhibiting amylase hydrolytic activity.This study provides a theoretical basis for applying protein fibril aggregates to foods with slowed starch digestibility.