Physico-Chemical Properties of Cross-linked and Hydroxypropyl White Sorghum (sorghum bicolor) Starch

Abstract

The study investigated the effects of cross-linking and hydroxypropylation on some physico-chemical properties of white sorghum (sorghum bicolor) starch. The sorghum starch (NSS) was isolated and chemically modified by hydroxypropylation with propylene oxide and by cross-linking with epichlorohydrin. The swelling, solubility and other physico-chemical properties of the starch was determined. The pasting property and the granule morphology of the starches were also determined using Rapid Visco-Analyzer and Scanning Electron Microscope respectively. Changes in chemical structure of the starch molecule were confirmed by FT-IR. The amylose content (27.01%) of the native sorghum starch decreased after modifications to (20.11 and 18.81) % for cross-linked, and hydroxylpropyl sorghum starches while the starch solubility and swelling increased in the temperature range (50 – 90oC), with the native starch having the highest values. Hydroxylpropyl sorghum starch (PSS) however has better swelling power in all the temperature range when compared with cross-linked sorghum starch (CSS). The shape of the starch granules was mainly spherical and polygonal with various diameters ranging from 6 to 22 μm, however modification does not have any pronounced effect on the starch granules. Hydroxypropylation reduced the breakdown viscosity of the native sorghum starch from 1630 to 1048 RVU, the peak viscosity of sorghum starch decreased from 2779 RVU for the native starch (NSS) to 2731 RVU in CSS. In conclusion, the modifications employed improved the physiochemical properties of sorghum starch and hence the modified starch could be used industrially.