| Rice is one of the important food crops in China and the population whose staple food is rice accounts for 60% of the entire Chinese consumer population.Paddy rice needs to go through a series of production and processes to become rice.In these links,rice will crack due to various reasons,thereby reducing the overall quality of rice,increasing food and economic losses.This study took the japonica rice widely planted in the middle and lower reaches of the Yangtze River as the research objects,used the X-ray imaging technology to detect the fissure,and classified the grains according to the degree of cracks,combined with the LF-NMR technology to explore the fissure development and variation of japonica rice.The influence of different factors on the percentage of fissured kernels and broken rice index(head rice yield and broken rice rate)were analyzed,and the relationship between them was discussed.Based on the characterization of the three-point bending mechanical properties,the influence of fissure on broken rice was analyzed,which aims to provide a certain theoretical reference for establishing crack detection methods,reducing the occurrence of cracks in rice,and ensuring rice quality.The main research contents are as follows:1.Based on the X-ray imaging technology,the percentage of fissured kernels and the degree of the fissure of japonica rice during the moisture desorption were studied.During the moisture desorption of japonica rice,the fissure changed significantly,and the fissured kernel percentage of Ruanyu,Huaidao 5,and Nanjing 5055 increased significantly after the moisture content was lower than 14.96%,15.21%,and 17.84%,respectively.The ratio of moderately fissured kernels and severely fissured kernels increased with the decrease of moisture content.During the moisture desorption,the fissure changes of the three types of japonica rice were different.To avoid excessive cracks in japonica rice,various japonica rice should be dried in different ways.The analysis of the correlation between fissure and moisture characteristics showed that the moisture state migration and the change of "bound water" content were the key factors leading to the changes of the fissure during the moisture desorption of japonica rice.The microstructure changes of fissure sections during the moisture desorption of Nanjing 5055 were studied.The microstructures of the fissure section of Nanjing 5055 at the cell level and starch granule level were significantly different.As the moisture content decreased,the proportion of intercellular sections increased,and the proportion of starch intermittent sections decreased.The discontinuous surface of the cell inside the grain was the fissure,but the fissure was very small and could not be observed.It existed in the kernel itself.The loss of moisture led to an increase in cell discontinuities,small fissure grew larger,and the disintegration of composite starch granules accelerated the propagation of fissure.2.The effects of variety,harvest period,and detection method on the percentage of fissured kernels and broken rice index(head rice yield and broken rice rate)of japonica rice were studied.Under the same moisture content,different factors had significant effects on the fissured kernel percentage of japonica rice(P < 0.05),and the significant effects of each factor on the percentage of fissured kernels were as follows:variety > harvest > detection method.There were differences in the percentage of fissured kernels obtained by different detection methods,but they all reflected the fissured kernel percentage of japonica rice harvested in the middle of the harvest period(60-66 days after heading)was lower than that of samples harvested in other harvest periods.The effects of variety,and harvest time on the head rice yield and broken rice rate were studied,and the correlation between the fissured kernel percentage and broken rice index was explored.Under the same moisture content,different factors had significant effects on the head rice yield and broken rice rate of japonica rice(P < 0.05),and the significant effects of each factor on the whole rice rate and broken rice rate were as follows: variety > harvest period.The percentages of fissured kernels detected by GB/T 5496-1985 and X-ray imaging were strongly correlated with the broken rice index of japonica rice(P < 0.01),but the fissured kernel percentage detected by X-ray imaging had a higher correlation with the broken rice index of japonica rice.The existence of fissure would significantly reduce the head rice yield of japonica rice(P < 0.05)and increase the production of broken rice.3.The three-point bending mechanical properties of whole rice kernels and fissured rice kernels were studied,and the effects of variety,harvest period,and drying method on the production of broken rice were analyzed.The exist of fissure would significantly reduce the mechanical properties of brown rice,making fissured rice kernels easier to break during processing,storage,and transportation,which reflected a positive correlation between the fissured kernels percentage and broken rice rate.Variety,harvest period,drying method,and fissure had extremely significant effects on the breaking force,breaking strength,and apparent modulus of elasticity(P < 0.01).The significant influence of each factor on the breaking force was as follows: harvest period > fissure > variety > drying method.The significant influence of each factor on the breaking strength was as follows: harvest period> fissure > variety > drying method.The significant influence of each factor on the apparent modulus of elasticity was as follows: fissure > harvest period > drying method > variety.There was a significant correlation between the physical and chemical indicators of japonica rice and the broken rice index(P < 0.05).The higher the protein content and total starch content,the lower the fat content,and the less likely the kernels to break. |
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