Influence of starch structure and starch granule -associated proteins on rheological properties of starch pastes

Xian-Zhong Han, Purdue University

Abstract

Components of starch granules were investigated to reveal the roles of components in the overall rheology of starch pastes and gels. In a reconstitution study, replacement of insoluble starch with soluble starch decreased the viscosity of pastes and reduced the stickiness of gels. Rice amylopectin fine structure was found to significantly correlate with paste breakdown. Proportion of long chains of amylopectin was negatively correlated and proportion of short chains positively correlated with paste breakdown. Influences of starch granule-bound starch synthase (GBSS) and other granule-associated proteins on rheological properties of starch pastes and gels were studied using a normal and three isogenic waxy (a waxy null and two GBSS-containing waxy mutants) maize starches. Starch granule-associated proteins, especially GBSS, reduced paste breakdown and viscosity of starch pastes. The viscoelasticity of pastes and gels was greatly reduced as more starch-granule-associated proteins were removed. Light microscopy of pastes suggested that starch granule-associated proteins influence the rheology of pastes through increasing the rigidity of gelatinized starch granules. The study indicated that starch granule-associated proteins, especially GBSS, can significantly change the rheological properties of starch pastes and gels despite its low concentration in starch pastes. Location of starch granule-associated proteins was revealed using a protein specific dye with confocal laser scanning microscopy. Starch granule-associated proteins were found to be concentrated in internal concentric rings in potato, maize, and wheat starches. Observation of granule proteins at different optical depths of field showed that proteins were distributed in discrete spheres. Amylose-free potato and waxy corn starch granules showed no internal protein spheres, indicating that the protein spheres are composed of GBSS and are likely associated with location of amylose. GBSS was also found to be strongly associated with isolated gelatinized granule remnants of normal potato, maize and wheat starches while virtually no protein was found in remnants of amylose-free potato and waxy maize starch. Starch granule-associated proteins, including GBSS, were found to be partially lost during alkaline extraction of rice starch. Variation in amount of loss in GBSS and other granule-associated proteins was found among different rice lines. Starch damage caused by ball milling was shown to reduce the viscosity and elastic nature of starch pastes. The study showed that soluble starch, amylopectin, and starch granule-associated proteins have their unique functions and contribute to the overall rheology of starch pastes and gels. Confocal microscopy of starch granule-associated proteins provided the structural/locational basis for the rheological function of GBSS in starch pastes.

Degree

Ph.D.

Advisors

Hamaker, Purdue University.

Subject Area

Food science

COinS