Barnyard millet starch cross-linked at varying levels by sodium trimetaphosphate (STMP): Film forming, physico-chemical, pasting and thermal properties

Abstract

Sodium trimetaphosphate (STMP) at different levels (1, 3 and 5%) was used to prepare cross-linked (CL) barnyard millet starch. The starches were studied for their physicochemical, pasting, steady shear rheological and thermal properties. Further, films were formulated from these starches and assessed for their functional and mechanical behavior. Amylose content of native starch (15%) decreased upon cross-linking (7.86–9.65%). CL starches had lower swelling power (SP) and solubility than native starch. CL starches showed lower peak (7049–9649 mPa.s), breakdown viscosities (BV) (1073–3172 mPa.s) but higher pasting temperature (PT) (79.7–80.8 °C) than native starch. Pasting properties were more affected for CL (5%) starch. Steady shear properties revealed lower yield stress (σo) values of CL starch pastes (1.39–2.37 Pa) than native starch paste (15.40 Pa). Flow behavior index was <1 for native and CL starches, thereby indicating their shear thinning behavior. Cross-linking increased gelatinization temperature, but decreased the enthalpy of gelatinization (ΔHgel) values. CL starch films exhibited lower water vapor permeability (WVP) and higher tensile strength (TS) and solubility than native starch films. CL (5%) starch film exhibited the lowest WVP (1.28 g.m/Pa.s.m2) and the highest TS (13.12 MPa) among films.