Studies Of The Factors Affecting Grain Physicochemical Quality And Its Determination In Rice

Starch is the main storage component in rice grain, and accounts for about 85-90 percentage of the dry weight of grain. Therefore, it is considered as the key determinant of rice grain quality. There needs a series of processing and handling process to purify starch from rice grains. Besides, the properties of isolated starch were affected by not only the rice variety, amylose content, pasting properties and other factors, but also the the particle size of isolated starch. In this study, with an aim to scientifically evaluate rice grain quality, we performed experiments to study the factors affecting the processing and quality of rice grains by using numbers of rice cultivars with different grain quality. The main results are as followings.1. The starch gelatinization properties of 222 rice varieties were measured by using three different methods, alkali spreading value (ASV), Rapid Visco Analyser (RVA) and Differential Scanning Calorimetry (DSC), respectively. The correlateionships between these three methods were analyzed, and the results showed that some of the conclusions obtained by means of above methods reflected both commom and varied aspects of starch gelatinization characteristrics. The RVA profile reflects the viscosity properties on starch gelatinization, DSC reflects in thermodynamic properties, and ASV indirectly reflected the characteristics of the gelatinization by the determination of alkali resistance. The results also revealed that there had a negativly remarkable correlation between ASV and RVA gelatinization temperature, and a negativly significant correlation between ASV and DSC thermodynamic properties. The RVA gelatinization temperature was negativly correlated withâ–³H, but positively with To, Tp or Tc. These results indicated that the gelatinization properties determined by DSC can completely represented that by ASV. And the pasting properties measured by both DSC and RVA could get a comprehensive interpretation of the gelatinization properties of starch.2. By using three rice cultivars with various grain quality, the effects of rice grain processing methods on rice flour quality and structure were investigated. The processing methods include dry-milling, wet-milling, water-drying or alcohol-drying. The results showed that, due to difference among rice varieties, the different processing ways have a different effects on the change of rice components. The effect was not consistency of all treaments on the paste viscosity and DSC gelatinization properties. But, less starch damage was observed by using wet-milling and alcohol-drying ways. Therefore, we shoud use appropriate method to process the rice grains based on the characteristics of different varieties and experimental requirements.3. The effects of seeds proteins on rice grain physicochemical qualities were also analyzed by using twelve rice varieties with different seed protein contents. Two different methods, alkaline or enzyme method, were used to deproteinization. The results shows that the physicochemical qualities were significantly changed after deproteinization. Besides, the paste viscosity and gelatinization properties were also distinctly changed. There was a negative effect of deproteinization on DSC gelatinization properties. The degree of crystal structure of deproteinization starch was increased after deproteinization treatment.