Physicochemical and rheological properties of cross-linked litchi kernel starch and its application in development of bio-films.

Abstract

In this study, starch from a non-conventional source, that is, litchi is extracted and cross-linked (CL) with varying concentrations (1%, 3%, and 5%) of sodium trimetaphosphate (STMP). The starches are characterized for their physicochemical, pasting, rheological, and thermal properties. Bio-films are also prepared from these starches and analyzed for selected barrier and mechanical properties. The results indicate that an increase in cross linking agent concentration resulted in a significant decrease in amylose content, swelling power (SP), and solubility of starches. Peak viscosity (PV) and breakdown viscosity (BV) of CL starches are lower in comparison to native starch. Steady shear properties reveal that magnitudes of yield stress (σo) and consistency index (K) decrease upon increase in the concentration of cross linking reagent. CL starches exhibit significantly (p < 0.05) higher transition temperatures than native starch. Native starch film shows water solubility of 43.66% while for films from CL starches, the values ranged between 35.12 and 41.53%. Significant (p < 0.05) reduction in water vapor permeability (WVP) values of CL starch films (1.24–1.52 g m Pa−1 s−1 m−2) is observed in comparison to native (2.32 g m Pa−1 s−1 m−2) starch films. Cross linking significantly improves tensile strength (TS) of films, however, films elongation is lower (14.71–17.97%) than native starch film (19.88%).