Studies on Physicochemical Properties of Rice Bean (Vigna umbellata) Starch: An Underutilized Legume

Abstract

Starch is a reserve carbohydrate present in plants. It is an important component for maintaining various quality attributes like texture, consistency, thickening in the food industry. The aim of the present study was to isolate starch from a legume named jack bean that is not very much famous and considered as underutilized-legume. The isolated starch was studied for various physicochemical properties. One-way analysis of variance was used in this study. The starch was isolated as a white powder from the dry legume by using standard method and the starch yield was observed to be 25.79%. Legume starch was further assessed for the chemical composition. The moisture, ash, fat, protein, fiber and carbohydrate content were 9.56%, 0.35%, 0.21%, 0.69%, 0.33%, and 89.19% respectively. The apparent and total amylose content was 37.62% and 40.83% with least gelation concentration at 6% of starch gel. Starch was further assessed for functional properties. The leached amylose displayed a rise in content from 6.56% to 9.50% with the corresponding increase in temperature from 65°C to 95°C that may affect gelatinization properties of starch. The water absorption capacity was 3.60 g/g while oil absorption capacity was 3.54 g/g. Further, the emulsion stability and emulsion capacity of native starch was 79.00% and 68.33% respectively that showed good stability of emulsion. Similarly, the swelling power and solubility of rice bean starch increased with the increase of temperature from 55-95°C. However, the opposite trend was observed for an increase in starch concentration from 1-4%. The effect of different concentrations at 6, 8 and 10% on freeze-thaw stability and storage studies showed that the expelled water decreased with the rise in starch concentration up to three consecutive storage days while no change was observed later during frozen gel storage. It showed good freeze thaw stability of starch. This underutilized legume attracted more attention from researchers due of its affordability and ease of availability. In dry farming circumstances with limited soil fertility, the legume yield consistently. Thus, this neglected legume that has minimal agronomic development but many qualities is a good substitute for starch. However, thorough study on the unique functional properties and other qualities of starch from rice bean has not been carried out. The results of this underutilized legume starch can provide opportunities to starch researchers and to the food industries that are frequently using conventional sources of starch from cereals, tubers and rhizomes.