Stratification Characteristics Of Rice Protein And Starch Under Different Nitrogen Application Conditions And Their Effects On Eating Quality

Eating quality is the most important sensory evaluation index of rice quality.As the two main components of rice,rice protein and starch determine the taste quality of rice to a large extent.In addition to the content of protein and starch,differences in the distribution of protein and starch in rice may also affect the taste quality of rice.However,the stratified distribution characteristics of rice protein and starch in rice and how they affect the eating quality of rice are not clear.Therefore,in this experiment,four rice varieties（HHZ,JFY,YY7850 and MXZ）with obvious differences in eating quality were used as materials.At the same time,different nitrogen fertilizer application levels were set(0 kg ha^-1and 200 kg ha^-1),through the layered milling of the rice grains（the grains are milled from the outside to the inside into 4 layers,L1（0%-9%）,L2（9%-14%）,L3（14%-19%）,L4（81%））,to study the stratification characteristics of different levels of protein and starch in rice grains under different nitrogen application levels,and their relationship with eating quality.The main results of this study are as follows:1.The application of nitrogen fertilizer significantly increased the total protein content of different types of rice,while the change rule of the total starch content affected by nitrogen fertilizer application was inconsistent,showing obvious differences between varieties.The protein content of rice increased by 37.2%-65.8%under nitrogen application;the total starch content of HHZ and JFY increased significantly under nitrogen application,while the amylose content was hardly affected.Under nitrogen application,the starch content and amylose content of YY7850 increased significantly,while the total starch content and amylose content of MXZ decreased significantly.2.From the perspective of protein content,in general,the protein content of each variety shows that the outer layer of rice is larger than the inner layer.Among them,HHZ and MXZ have the highest protein content in the L2 layer,and JFY and YY7850are in the L1 layer.From the perspective of protein components,the content of different stratified protein components in each variety is glutelin>globulin>albumin>prolamin.Albumin,globulin and prolamin are mainly distributed in the L1and L2 layers,while glutelin is relatively evenly distributed in the inner and outer layers.From the perspective of protein structure,the secondary structure of different hierarchical proteins of each variety isα-helix>β-sheet>β-turn>random coil.From the outer layer to the inner layer,theα-helix showed a trend of increasing first and then decreasing,the highest in the L2 layer,and theβ-sheet showed a trend of first decreasing and then increasing,and the lowest in the L2 layer.From the perspective of starch content,in general,starch and amylose are mainly distributed in the inner layer,and gradually increase from outside to inside in rice grains.Nitrogen application had significant effects on protein content,composition and starch crystallinity in different layers of rice.3.The cooking and eating quality of rice showed a trend of increasing gradually from the outer layer to the inner layer,and the difference in eating quality was closely related to the changes of protein and starch at each layer.From the point of view of protein,protein content,albumin,globulin,and glutelin at all layers were extremely significantly negatively correlated with peak viscosity and breakdown,and significantly or extremely significantly positively correlated with final viscosity,setback and pasting temperature,and significantly negatively correlated with the taste value.There is a significant negative correlation between gluten at all levels and taste value.From the perspective of starch,the starch and amylose content of each layer was extremely significant positive correlation with peak viscosity and breakdown,and extremely significant negative correlation with final viscosity,setback and pasting temperature,and extremely significant positive correlation with taste value.With the increase of the grinding degree of rice,the taste value of rice showed a trend of first increasing,then decreasing and then increasing.After grinding off the L2 layer,the taste value of rice decreased significantly.Therefore,whether the L2 layer is retained or not has a more critical impact on the taste of rice.4.Overall,rice appearance and processing quality decreased with increased rice grain milling.As the rice is milled in layers from the outside to the inside,the chalkiness degree of the rice increases significantly,and the length to width decreases,the proportion of head rice decreases significantly.After milling to remove the L2layer,the appearance quality and processing quality of rice decreased significantly.To sum up,the protein and starch distribution characteristics of different layers of rice with different tastes are significantly different,and this difference has a significant impact on the eating quality of rice.In general,increasing the content of starch and amylose in the inner layer of rice grains,reducing the content of protein in the inner layer of rice grains,including albumin,globulin and prolamin,and controlling the rice milling degree between 9%and 14%,can effectively improve the taste quality of rice.