Native and processed legume seed microstructure and its influence on starch digestion and glycaemic features: A review

Legume seeds are known to possess low glycaemic features and high levels of resistant starch. The seed microstructure, i.e., the arrangement of starch in cotyledon cells and interactions of starch with other non-starch macromolecules (protein, lipids, fiber) during processing, has been suggested to be responsible for these unique properties. The influence of various types of processing on their native microstructures and functional characteristics and the subsequent impact on their glycaemic features have not been examined. This review outlined two forms of legume seed microstructure (pulse cotyledon cells and pulse flour) that can be generated from whole seed during processing. The microstructural features of each form of microstructure generated and their subsequent influence on starch digestion properties was discussed. The interactions between the above-mentioned microstructural features differ significantly and influence the functionality of the legumes and their processed products. The rate of starch digestion decreased in this order; seed flour > cotyledon cells > whole seed. Cell walls and protein matrix act as primary and secondary physical barriers responsible for modulating the activity of the starch degrading enzymes for various legumes and pulses. Summarily, the intactness of the seed microstructure is a significant factor that affects the rate of starch digestion in whole pulse-based food ingredients. Whole pulse seed and pulse cotyledon cells have shown the potential for the development of low glycaemic foods. However, optimization of the extraction yield of intact cotyledon cells and the sustainable use of the enormous waste generated during the extraction procedure should be further investigated to maximize their food application prospects.