Zeta potential (ζ) and pasting properties of phosphorylated or crosslinked rice starches

Zeta potential (ζ) measurement is not only applied for estimation of colloidal stability but also used for the rapid determination of degree of substitution (DS) of phosphorylated or crosslinked rice starch, obtained by the reaction of rice starch with STPP (sodium tripolyphosphate) or STMP (sodium trimetaphosphate), respectively. The introduction of the phosphate groups into the starch molecules by these reagents enhances the negative charge on the starch particles, which relate to the zeta potential (ζ). The data from ζ and chemical analysis of DS were used in a regression analysis for developing a linear correlation to express the DS and ζ value and some RVA-pasting properties of phosphorylated or crosslinked rice starch based on the Çvalue. For the phosphorylated starches, linear relationships among DS, ζ value and peak viscosity (PV) as well as breakdown (BD) with a high correlation value (r²) were obtained. ζ value decreased with increasing DS, PV and BD, and with the decrease of pasting temperature (PT). For the crosslinked starches, linear relationships with a high correlation value (r²) among DS, ζ value and PV as well as BD were obtained. ζ value decreased with increasing DS and PT, in contrast with the decreasing of PV and BD. The ζ measurement can be used for the calculation of DS of the phosphorylation or crosslinking reactions. Some RVA-pasting properties of native or modified rice starches can also be predicted from the ζ value.