2.6 Determination of rice appearance, milling, cooking and eating quality
For rice appearance quality, chalk characteristics of brown rice were observed by the cleanliness test-bed according to our previous studies (Tang et al., 2019). Rice grains were milled using a mini universal grinder and dried over a 200-mesh sieve. Use vernier calipers to determine the length, width, and thickness of brown rice, and calculate the ratio of length to width. 300 grains of brown rice were randomly selected to detect chalky rice grains, and calculate chalky rice rate based on the percentage of chalky rice in the total number. Chalkiness area is determined by the proportion of chalky grain area to total grain area.
Rice milling quality includes three indicators: brown rice rate, polished rice rate and polished rice rate. During the maturity period, 30 rice panicles with uniform maturity were randomly harvested. After threshing, the grains were naturally dried with the moisture content to 15%. Brown rice percentage (BRP) and milled rice percentage (MRP) were determined by the processing machinery SY88-TH & SY88-TRF (Wuxi Shanglong Grain Equipment Co., Ltd., China), respectively.
Rice cooking and eating quality was determined by the RVA-4500 (a rapid viscometer developed by Newport scientific instruments, Australia). Weigh 3.00g rice flour with moisture content of about 14.0% into aluminum box, add 25ml distilled water, and stir it up and down rapidly for 10 times with an agitator to make the rice flour disperse evenly. The determination of RVA characteristic parameters for rice flour was programed as follows: the rice flour solution sample was heated at 50 ℃ for 1 min, then heated to 95 ℃ within 3.8 min, heated at 95 ℃ for 2.5 min, then cooled to 50 ℃ within 3.8 min, and finally heated at 50 ℃ for 1.4 min. The characteristic parameters of RVA spectrum include: peak viscosity (PKV), hot paste viscosity (HPV), cooling paste viscosity (CPV), breakdown viscosity (BDV), and depletion value (setback viscosity, SBV).