LIGHT AND SCANNING ELECTRON MICROSCOPE STUDIES ON DRY BEANS: EXTRACELLULAR GELATINIZATION OF LIMA BEAN STARCH IN WATER AND A MIXED SALT SOLUTION

Abstract

ABSTRACTGelatinization temperatures of freely dispersed Lima bean starch were determined in pure water and a dilute aqueous salt solution. The composition of the salt solution was based on the hydration medium employed to process quick‐cooking beans. Morphological changes in the starch granules during the gelatinization process were examined microscopically. In either an excess of pure water or salt solution the dispersed granules expanded and exhibited a characteristic sequence of explicit configurations. Various stages of gelatinization were characterized in light or scanning electron photomicrographs as: (1) swollen; (2) dimpled or indented; (3) doughnut or erthrocyte‐like; (4) rubber‐raft shaped; (5) pancake; and (6) dispersed or diaphanous. The dispersed granules retained a veil‐ or film‐like residue which has been defined as a “membrelle.” Gelatinization was initiated at a specific temperature and progressed to completion over a limited temperature. With increasing temperatures, the proportion of granules affected increased until all the granules were dispersed. The gelatinization temperature range was 71–79°C in water and was 79–85°C in the salt solution.