Composition and physicochemical properties of starch from pearl millet grains

The physicochemical properties of starches isolated from three cultivars (ICTP 8203, ICMS 7703 and ICMH 356) of pearl millet grains were studied. The yield of the starch was in the range 53–56% on a whole grain basis. The starch granules were round or polygonal with numerous indentations and pores on their surface. The free, bound and total starch lipids ranged from 0.04 to 0.08%, from 0.40 and 0.47% and from 0.44 and 0.55%, respectively. In all starches, neutral lipids (NL) and phospholipids (PL), respectively, formed the major lipid class in the free and bound lipid extracts. The major fatty acid in the NL fraction being linolenic acid, whereas palmitic acid was the major fatty acid in PL and glycolipid fractions. The total amylose contents ranged from 28.8 to 31.9%, of which 14.6–17.2% were complexed by native lipid. The X-ray pattern was of the A-type. The intensities of the major diffraction peaks followed the order: ICMS > ICTP > ICMH. The swelling factor followed the order: ICTP > ICMH > ICMS. All three starches exhibited identical pasting temperatures, but they differed with respect to the Brabender viscosity at 95 °C (ICMH > ICTP > ICMS), and the extent of increase in viscosity during the holding cycle at 95 °C (ICMS > ICMH > ICTP). The gelatinization temperature ranges were: 61.2–70.5 °C (ICTP), 60.9–67.5 °C (ICMH) and 64.5–78.0 °C (ICMS). The enthalpy of gelatinization (cal g−1) were: 2.7 (ICTP), 2.5 (ICMH), 3.5 (ICMS). The extent of hydrolysis by porcine pancreatic α-amylase and 2.2 n HC1 followed the order: ICTP > ICMH > ICTP. The percentage light transmission followed the order: ICTP > ICMH > ICMS. The stability towards freeze-thaw cycling followed the order: ICMS > ICMH > ICTP. The retrogradation endotherm was broader than the gelatinization endotherm (ICTP > ICMS > ICMH). In all starches, the melting temperature (Tp) of the retrogradation endotherm increased only marginally during storage. The increase in the enthalpy of retrogradation (ΔHmR), however, was much higher in ICTP than in ICMS and ICMH.