Controlling the Properties of Starch from Rice Brokens by Crosslinking with Citric Acid and Sodium Trimetaphosphate

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Abstract
Starch from broken rice of an Indian variety (PR114) is crosslinked by citric acid (CA, 12–60%) and sodium trimetaphosphate (STMP, 6–30%) to study structural, morphological, functional, rheological, and thermal properties. The formation of new peak of C═O stretching vibration at 1730 cm–1 by CA and the reduction of ─OH stretching at 3260 cm–1 by STMP starches in the FTIR spectra confirm crosslinking reaction. The XRD pattern reveals reduction in crystallinity of crosslinked starches; however, characteristic peaks disappear with increasing concentration of CA. SEM micrographs show STMP granules are comparable with polygonal shaped and smooth surfaced native granules. However, CA starches show irregular shape, rough surfaces, and growing agglomerates. The effect of crosslinking on pasting properties is detrimental due to reduction in swelling index and solubility. The significant reduction in peak viscosity and flattening of viscosity curve confirms the higher degree of crosslinking (85.60–99.37%). However, crosslinked gels become more flowable, show shear thinning behavior for STMP, and behave differently for CA starches. The dynamic rheology reveals that only native and STMP (6–18%) starches form a solid like paste. In addition, the STMP starches have higher gelatinization temperature, lower enthalpy, and better thermal stability than native starch.

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