Study On Eating Qualities Analysis And Comprehensive Evaluation Of Rice With Different Milling Degree

As one of the most important cereal crops in the world, rice has become a staple food for over half of the world population. In current time, fine processing products are the major supply form of rice, which result in loss of nutrients, low milling yield of rice and high energy consumption. If we do reasonably well milling for rice, that is to say lightly milling for rice, it will make full use of original nutrients of brown rice. Reasonably milling of rice can reserve nutrients, heighten rice milling yield, and lower energy consumption of milling. However, cooking properties and eating qualities of rice will also be certainly influenced. At the present time, research on cooking properties and eating qualities of lightly milled rice is not very comprehensive in our country. Especially the objective evaluation of eating quality and the establishment of evaluation system has not been reported.Therefore, Japonica rice (Kongyu131) and Indica rice (Waiyin7 and Denong 108) were selected for this paper to analyze the effects of degree of milling on chemical components, thermal properties, cooking properties, textural properties, and to study eating quality evaluation of lightly milled rice with different milling degree. Based on this, the model for rice eating quality evaluation was established. The results are as follows:Effects of degree of milling on optical properties, main chemical components, pasting properties were researched. The optical values such as whiteness, transparency, milling degree was found to be positive correlated with degree of milling level. The moisture content, crude protein, crude fat and crude fiber was found to be negatively correlated with milling degree level. The peak viscosity, trough and breakdown of rice flour was increased with the increased in degree of milling but setback and gelatinization temperature decreased with the increased in degree of milling, while gelatinization enthalpy increased first and then decreased.In research of cooking and eating qualities for lightly milled rice with different milling degree, indicating that the color parameters rice brightness (L*) and whiteness (WI) was positive correlated with degree of milling, while its redness (a*) and yellowness (b*) was negatively correlation. There were many axial fissures of cooked rice samples when degree of milling ranged from 0% to 4%, and few in the range of 6%～8%, but the rice samples milled to 10% with axial fissures and unsmooth outer surface. The cooking properties such as water uptake ratio, volume expansion ratio, elongation ratio, iodine blue value and solid content in residual cooking water increased with increase in degree of milling, but optimal cooking time decreased. It showed that amylose content, gel consistency, alkali spreading values and the adhesiveness of cooked lightly milled rice samples increased with the increase of milling degree, while hardness values and chewiness of cooked rice was plotted against degree of milling for the three varieties rice.Correlation analysis between sensory characteristics of cooked rice and other indexes indicated that there was correlation between sensory characteristics and physicochemical indexes, pasting indexes, cooking properties, eating qualities. The evaluation model for rice eating quality established based on those property indexes using principal component analysis. The moisture content, crude protein, crude fat, crude fiber, amylose content, gel consistency, whiteness of cooked rice, peak viscosity, trough, onset gelatinization temperature, iodine blue value in residual cooking, hardness, adhesiveness and other seven indexes were choosing for principal component analysis. Rice eating quality evaluation model " F=a1×X1+a2×X2+a3× X3+a4 × X4+a5 × X5+a6 × X6+a7 × X7+a8 × X8+a9 × X9+a10 × X10+a11 × X11+a12 × X12+a13 × X13+a14 × X14+a15 × X15+a16 × X16+a17 × X17+a18 × X18+a19 × X19+a20 × X20 " was established for Kongyul31, Waiyin7 and Denong 108, respectively. And sensory evaluation was employed to examine those models. It showed a good consistency between them. This indicated that this method could use to evaluate the eating quality of lightly milled rice, and it can reflect the effects of degree of milling on the change of eating qualities of lightly milled rice objectively.