Effect of oxidation and crosslinking on functional, rheological and thermal properties of oat and apple starches

Abstract

Oat (Oa) and apple (Ap) starches were isolated and chemically modified by oxidation with 10% NaOCl to obtain oxidized starches (OOa and OAp), followed by cross-linking with a mixture of 5.6 g of sodium tripolyphosphate and 11 g of sodium trimetaphosphate to obtain doubly modified starches (OCOa and OCAp). In the native and modified starches, the functional properties (swelling power and solubility, and freeze-thaw stability) and thermal and rheological properties (steady-state flow curves and paste formation profile) were evaluated. The swelling power of native and double modified starches varied from 57 to 86 g/g and the solubility from 0.8 to 6.0 g/100 g, these variables increased as the study temperature increased; the increment in these properties was greater in Oa compared to Ap. Oxidation followed by crosslinking increased the freeze-thaw stability in Oa and Ap starches at 30, 60, 75, and 90 °C. It also increased the Tg of OCAp and OCOa ≈ 9% compared to the native samples, respectively; while an inverse pattern was observed in apparent viscosity were this value decreased ≈ 0.8 Pa × s for Oa and ≈ 0.5 Pa × s for Ap compared to the double modified samples. All samples presented a thinning cut-type behavior (pseudoplastic), indicating structural differences. Cross-linking in oxidized starches produced a reinforcing matrix that was determined in the paste formation profile. Dual modification (oxidation-cross-linking) could be an alternative for using starches from underused botanical sources, such as apples and oats, with different functional properties and feasible applications in food systems.