Effect of gelatinizing temperature and moisture on the retrogradation of coix starch

Abstract

Growing snacking trends are boosting the market demand for pre-gelatinized seed flours and the degree of crystallinity of gelatinized starch could be a useful determinant of shelf life and quality. We investigated the effect of gelatinization temperature on purified coix starch (PCS) and the role of added moisture on retrogradation of gelatinized PCS at different temperatures. Disruption of granular structure of PCS with progressive agglomeration resulted in the formation of gelatinized mass with increasing gelatinizing temperature. Amylose content, hydration, degree of gelatinization (DG) and peak viscosity increased while relative crystallinity and short-range structures decreased with elevated gelatinizing temperature. Retrogradation of PGCS increased crystallinity with reduced hydration, peak viscosity without significant change in flow properties and amylose content. Thermal decomposition of PGCS occurred at lower temperature with elevated gelatinizing temperature. PCS was more resistant to thermal decomposition as compared to PGCS. The degree of crystallization affected by added moisture suggested the disruption of molecular arrangement. Higher moisture levels were required for PGCS with lower DG for crystallinity during retrogradation whereas low moisture levels were needed for PGCS with greater DG. Controlling moisture level seems to be critical for the quality and shelf life of the products derived from gelatinized PCS.

Keywords: Coix starch; Decomposition; Gelatinization; Moisture; Retrogradation.