| Rice industry is an important basic agricultural industry in Jiangsu Province.According to the plan of“building Jiangsu Province into a land of fish and rice in new era”,the whole province spare no effort to promote the development of high-quality rice industry in recent years.It is really urgent to screen high-quality rice varieties and improve the eating quality.At present,the conventional rice cultivation types in Jiangsu Province are soft rice(semi-glutinous japonica)and ordinary japonica rice.The soft rice has the features of low-amylose content and high eating quality,and the cultivation area reaches half of the total cultivation area in Jiangsu Province.However,the evaluation criteria of our country are one-sided,which can't reflect the real condition of rice quality in Jiangsu Province objectively.Therefore,it is extremely vital to study the rice quality and establish a suitable evaluation system for high-quality rice in Jiangsu Province.This study conducted a comprehensive and systematic quality evaluation of 74japonica rice,and explored the key indicators that affected the rice-eating quality to establish the japonica rice evaluation criterion for Jiangsu Province,illustrated the mechanism that influencing rice eating quality,and provided theoretical support for the cultivation of high-quality rice.1.The milling quality,appearance quality,physicochemical quality,and cooking and eating quality of 43 soft rice and 31 common japonica rice were systematically contrasted and analyzed.These results showed that the milling quality and appearance quality of soft rice were generally inferior to common japonica rice.Compared with common japonica rice,soft rice had lower average head rice rate(59.14%),higher the average chalky grain rate(26.02%)and the average chalkiness(7.43%).The physicochemical quality between soft rice and common japonica rice were significantly different.The average amylose content of soft rice(5.58%-10.04%)was significantly lower than that of common japonica rice(13.20%-23.58%),and the average protein content(7.07%)of soft rice was lower than that of common japonica rice(7.48%).The better eating quality was found in soft rice.The taste value and sensory score of soft rice were higher than that of common japonica rice,and the lower hardness(3.69 kgf),higher stickness(0.71 kgf)and elasticity(0.71)were observed in soft rice.Soft rice exhibited higher mean peak viscosity value,breakdown value,lower mean final viscosity value and setback value by comparison to common japonica rice.Therefore,soft rice was relatively characterized as low amylose,high palatability and high chalkiness.2.Correlation of the physicochemical quality,cooking and eating quality of soft rice and common japonica rice were analyzed.These results showed that the taste value of soft rice was positively correlated with amylose content(R~2=0.7137),but did not correlate with protein content.The taste value of common japonica rice was negatively correlated with the content of protein and amylose(R~2=0.7941?R~2=0.3455).The amylose content of soft rice and common japonica rice was significantly negatively correlated with the breakdown value(p<0.01),and was extremely significantly positively correlated with the setback value(p<0.01).The taste value of soft rice was significantly negatively correlated with the breakdown value(p<0.05),and was significantly positively correlated with the setback value(p<0.05).The taste value of common japonica rice was significantly positively correlated with the breakdown value(p<0.05),and was significantly negatively correlated with the setback value(p<0.05).As for soft rice,the better eating quality can be ascribed to the lower breakdown value and higher setbanck value.The soft rice possessed a moderate hardness and stickness with soft but not rotten texture.Meanwhile,soft rice and common japonica rice had better taste value with breakdown value between 800 c P-1200 c P and setback value between 500 c P-800 c P.3.The physicochemical properties and structural properties of starch in soft rice and common japonica rice and their correlations were further studied.These results showed that soft rice starches presented lower amylose content,higher peak viscosity value and breakdown value,lower final viscosity value and setback value,stronger gel network compared with common japonica rice starches.Besides,the water solubility index and swelling power of soft rice starches and common japonica rice starches increased with the increase of temperature.The particle size distribution results showed that the particle size distribution of soft rice starches was greatly affected by the gene,and the proportion of small particles was higher,D50and D90 were wider than that of common japonica rice starches.The crystalline structure showed that soft rice starches had greater crystallinity and the degree order,while the thickness of the semi-crystalline layer was smaller.The molecular structure presented that the molecular weight,branch density and short branch chains proportion of soft rice starch were higher,but the long branch chains proportion were lower than that of common japonica rice starches.Correlation analysis showed that the amylose content and the chain length distribution of amylopectin were the major factors that affected the physicochemical properties and structural properties of rice starches.4.The relationships among starch physicochemical properties,structural properties and eating quality of cooked rice were determined using Pearson correlation analysis.The results showed that amylose content significantly positively correlated with hardness(p<0.05),and extremely significantly negatively correlated with stickness(p<0.01).The molecular size and chain length distribution of starch were important factors that affected the hardness and stickness of cooked rice.The hardness was significantly positively related with the long branch chains(B2 and B3)of amylopectin(p<0.05),and stickness had a significant positive correlation with short branch chains(A and B1)of amylopectin(p<0.01).Therefore,the proportion of short branch chains and long branch chains of amylopectin were the main factors thataffected the eating quality of soft rice and common japonica rice. |
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