Zeta potential (ζ) analysis for the determination of protein content in rice flour

Abstract

Zeta potential (ζ) analysis was investigated as a means of rapid determination of residual protein content of rice flour during processing of rice starch. A rice flour sample was suspended in 0.3% sodium hydroxide solution to obtain rice flour slurry which was subjected to protein extraction by a decanter for five cycles. The samples from all cycles were collected, neutralized, dried, sieved through a 200 mesh sifter and subjected to ζ analysis. The data from ζ values (y) and chemical analysis of protein content (x) from six samples of rice flour were used in a regression analysis to develop an empirical equation to express the protein content of rice flour based on ζ value alone. The result of ζ value obtained from six samples of different protein contents suspended in a buffer solution of pH 12 yielded a standard linear equation of y = -1.29×-12.51. In another method of ζ analysis, the sample was suspended in DI (deionized) water without buffer by varying pH from 2 to 8 for the ζ measurement. A linear relationship between ζ and pH was obtained together with the constant value k (slope) which could be converted into protein content (x) of rice flour by a standard linear equation of k = -1.15×-4.90.