Hydroxypropylation of pigeon pea (Cajanus cajan) starch: Preparation, functional characterizations and enzymatic digestibility

Hydroxypropyl starch derivatives were prepared from pigeon pea starch (NPPS) which is an unconventional starch source. Functional parameters and characterization of both native and modified starches were carried out. The starch granules appeared oval or elliptical in shape with sizes ranging from 7 to 40 μm in width and 10 − 30 μm in length. Hydroxypropylation did not alter the shape of the starch granules in a pronounced way. Generally, the x-ray diffractograms of native pigeon pea starch showed the “A” pattern. However, slight reductions in the diffraction intensity of starches after modification were observed. At all temperatures studied (30-90 °C), swelling and solubility of hydroxypropylated starches were higher than the NPPS. Progressive increases in swelling capacity and solubility were observed as the molar substitution (MS) increased among the hydroxypropylated starches. Hydroxypropylation reduced starch paste turbidity on storage. Also, studies showed that syneresis reduced after hydroxypropylation. In addition, syneresis reduced as the MS of the hydroxypropyl starches increased. The results indicate that pasting temperature and peak temperature reduced after modification but peak viscosity increased in hydroxypropylated starch derivatives compared with the native starch. Setback reduced in hydroxypropylated starches compared with the native starch. Enthalpy of gelatinization and percentage retrogradation reduced after hydroxypropylation and progressive reductions were observed as the MS increased among the starch derivatives. Hydroxypropylation increased enzymatic digestibility.