The isolation and characterisation of starches from legume grains and their application in food formulations
Creators: name: Lee, Horng
Publisher: name: RMIT University
Year: 2024

description: As a major group of agricultural commodities, legume grains are widely grown and consumed globally, but are often utilised in the whole form. With increasing evidence of nutritional benefits, these grains are potentially sources of novel ingredients including starches. Accordingly the objective of this study has been to investigate legume starches, particularly their isolation, characterisation and incorporation into selected food products. Using chickpea, faba bean, lentil and mung bean, extraction procedures for the practical isolation of legume starches have been evaluated. A relatively simple method has been established, involving grain cracking, steeping in a mildly alkaline solution, followed by washing, double blending, double sieving and sedimentation. The starches collected for the four legumes were oven dried and the recoveries ranged between 29 and 38%.<br><br>Compositional analyses confirming that the isolation procedure gave relatively pure starches and scanning electron microscopy showed that the granules were typically ellipsoidal. Laser particle size analysis showed mono-modal distributions with mean diameters between 19.6 and 23.9µm. X-ray diffractograms of legume starches were of the typical C-type, with variations in the intensities and peak distribution indicating some differences in the crystallinity of the starches. Suitable conditions for the measurement of starch gelatinisation characteristics by differential scanning calorimetry were investigated. When optimised conditions were applied, the temperature of gelatinisation ranged from 58.9 for lentil to 65.7 °C for mung bean with corresponding enthalpy values of 9.2 and 5.7 Jg-1. Hot-stage optical microscopy confirmed gelatinisation patterns. The starch pastes demonstrated opalescence with some variation in the degree of clarity. The pasting and viscosity properties measured by the Rapid Visco-Analyser showed some variation in pasting temperatures and considerable differences in peak readings with faba bean starch having lowest and mung bean the highest with values of 307 and 676 RVA units, respectively.<br><br>In order to study the incorporation of the legume starches, two Asian food products having starch as an ingredient, were selected and adapted as model foods. In this context, vermicelli represented a savoury product and coconut cake a sweet product. Vermicelli and coconut cake samples that incorporated chickpea starch were both preferred by most of the panellists over those containing the other legume starches.<br><br>The overall conclusions are that the starch extraction method adapted in this investigation was a practical approach, producing relatively pure, white starches. The characteristics of the four legume starches showed many similarities, but there were some variations in the properties, indicating that there may be different applications for their incorporation into food formulations. Sensory evaluations confirmed the usefulness of the starches as food ingredients that provide attractive mouthfeel and textural characteristics. Therefore legume starches offer potential as novel food ingredients warranting further evaluation and larger scale feasibility studies.<br>