Functional and Microstructural Aspects of Soluble Corn Starch in Pastes and Gels

Abstract

Soluble starch plays an important role in the rheology of starch pastes and gels. However, some functional aspects and the microstructural basis of its contribution are still not clear. In this study, commercial corn starch was pasted in a Rapid Visco Analyzer to peak viscosity, and separated into soluble starch (clear of granules and primarily amylose) and insoluble starch (gelatinized starch granules and primarily amylopectin). When the insoluble starch was reconstituted at different levels with soluble starch, paste viscosity profiles in the Rapid Visco Amylgram decreased with addition of increasing amounts of soluble starch. Cold stage scanning electron microscopy (SEM) of pastes revealed a continuous cellular structure of the sample without soluble starch and a denser fibrous structure of the one with soluble starch. Texture analysis of gels formed from pastes showed that the firmness of the gel increased, while gel stickiness decreased, with increasing amounts of added soluble starch. Cold stage SEM of gels revealed a fibrous structure of the gels with the addition of soluble starch and a cellular structure of the gels consisting of insoluble starch alone. Decrease in gel stickiness with addition of the amylose-rich soluble portion implies a large contribution by amylopectin or starch remnants to sticky gel texture. The microstructural comparison of pastes and gels with and without soluble starch provides a structural explanation for the function of soluble starch in pastes and gels.