The effects of alkaline extraction on the characteristics of lima bean (Phaseolus lunatus) starch

Abstract

This study provides an overview of the use of lima bean (Phaseolus lunatus L.) flour as a raw material for starch extraction in consecutive steps for the preparation of lima bean protein concentrate. The starch from lima bean flour was extracted at different alkaline pH levels: 7, 8, 9, 10, and 11. The physicochemical, microstructural, crystallinity, pasting, and functional properties of the extracted starch were evaluated. The results showed that the purity of the starch increased with a higher extraction pH. However, a further increase in pH reduced the yield. The alkaline-extracted starch still contained other non-starch compounds. The extraction pH affected the amylose content, presumably due to the interaction of OH- ions with the starch granular components, influencing the yield and amylose level. At lower pH levels, alkali promoted a more orderly granular structure, decreasing starch solubility and resulting in higher yield and amylose content. Meanwhile, at higher pH levels, alkali ions increased protein solubility and starch content. The pH had a slight influence on the starch granule morphology. Lima bean starch exhibited a crystallinity index of 29% to 34% depending on the alkaline extraction pH. All starches showed individual peaks at 2θ values of 15° and 23°, unresolved peaks at 2θ values of 17° and 18°, and a diffracted plane around 5.63°, indicating a C-type starch. After alkali treatment, the starch maintained its C-type structure, indicating no structural transformation in the orthorhombic and hexagonal structures. Increasing the extraction pH to 9 increased starch crystallinity, but a further increase in pH decreased it. Viscosity during pasting was affected by the intensive interaction of water with amylose in the amorphous regions. The extraction pH influenced peak, trough, setback, and final viscosity. The alkaline treatment might disrupt granular regions, altering the functional properties of the starch. Alkaline extraction of starch can be performed on lima bean flour.