Effect Of Rice Yellowing On Physicochemical Properties,Structures And Rheological Properties

In this study,the PHY and normal rice of Feng liangyou japonica rice,Yanfeng 47 indica rice,glutinous rice and other varieties were used as raw materials.The thermodynamic properties,viscosity characteristics and internal crystal structure characteristics,rheological properties,dynamic hygroscopic properties,internal structural morphology and in vitro digestibility were measured,in order to compare with the differences in the physical and chemical properties between normal rice and PHY rice.The analysis of thermodynamic properties showed that the peak temperature and enthalpy of the yellowing rice were lower than normal rice correspondingly,and there was no significant difference between the gelatinization start temperature and the end temperature,and the yellowing process resulted in the peak viscosity and disintegration value of rice,the retrogradation value showed different trends,indicating that PHY has a more organized structure.Current rheological studies have shown that the storage and loss modulus of gels formed from PHY rice are lower than their corresponding normal rice samples,and yellowing process significantly reduces the area of the hysteresis loop,after yellowing the resilience of rice is stronger than normal rice,which means the PHY rice is not easy to be damaged by external force,and it is easy to return to the state before shearing.The gel strength of yellowing rice is weaker than that of normal rice,the ability to restore its original shape is enhanced,and the ability to resist flow is enhanced,which is inseparable from the structural change.The interior of the rice changes during the yellowing process is reduced,as well as the flexibility and strength of rice.Therefore,we believe that yellowing can inhibit the formation of a continuous network structure due to changes in the internal structure of rice grains during yellowing,thereby weakening the gel network of starch.This paper research the internal structure of rice grains by moisture adsorption kinetics and low-field NMR,which aims to study the existence and migration of water in different rice.The results show that under the conditions of normal temperature and humidity,the yellowing process makes the rice has faster moisture absorption and dehumidification process compared with ordinary rice correspondingly,and the water mobility inside the rice is improved after yellowing.This process may be related to the presence of "capillary channels" inside the rice induced by the yellowing process.Experiments of scanning electron microscopy and in vitro simulated digestibility show that the surface of the rice after yellowing is rough,the particles partially collapse and the surface adheres to small particles.Accompanied by small holes with different sizes,and a small part of the cracks attached to the surface,while normal rice shows sharp edges,clear particles,smooth surface.The digestibility of PHY is higher than normal rice,yellowing may induce"capillary the role of the channel",these structural features may be related to the accelerated diffusion of digestive enzymes in rice grains.Finally,the rice before and after yellowing was treated by different concentrations of acid solution.The thermodynamic properties indicated that acid treatment caused a sharp increase in ΔT,the ΔT and ΔH of PHY were smaller than ordinary rice,which means the yellowing process leads to a more systematic structure of rice.The results of XRD and SAXS consistently showed that the crystallinity of PHY and ordinary rice did not differ much under the hydrolysis of low concentration sulfuric acid solution consistently,but the crystallinity of all samples are decreased,with the treatment of lmol/L sulfuric acid solution,rice samples form new crystallinity area,especially PHY rice,the morphology of PHY and ordinary rice is not significantly different before and after sulfuric solution treatment.