2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

Rice starch is commonly isolated by alkaline steeping method because the method results in high yield and high purity of rice starch. However, the cost of treating alkaline effluent from the isolation process is prohibitive in producing commercial scale of rice starch. This study attempted to use proteases at neutral pH conditions to assist in removing protein from rice starch without the usage of alkali, thus greatly reducing the waste water treatment cost. Acidic, neutral, and alkaline proteases (three levels each) reacted with rice flour slurry at pH 6.5 and 50 C for 18 hrs. Starch isolated by the alkaline steeping method was used as the control. The starch yield ranged from 68.2 to 77.6% (starch dry basis); the protein and damaged starch contents of isolated starches ranged from 0.07 to 0.33% and from 1.5 to 2.3% (starch dry basis), respectively. The pasting properties of isolated starch as measured by a Rapid Visco-Analyzer were significantly affected by the presence of protein and damaged starch. The protein content was positively correlated with the breakdown viscosity (r=0.58, p<0.05), while the damaged starch content was negatively correlated with the pasting time (r= -0.77, p<0.05) and the peak viscosity (r= -0.78, p<0.05). All isolated starches exhibited similar thermal properties as determined with differential scanning calorimeter. Acidic, neutral, and alkaline proteases yielded comparable quantity and quality of rice starches as the alkaline steeping method, but did not generate alkaline effluent in the process.