Chapter 8 - Cotyledon Cell Structure and In Vitro Starch Digestion in Navy Beans

Abstract

The physicochemical and microstructural characteristics of navy beans are important in relation to their starch digestibility. The microstructure of raw and cooked beans consists of hexagonal- or angular-shaped cotyledon cells (50–100μm size) containing starch granules. The flour obtained through milling of the whole navy beans contains disrupted cotyledon cells, starch granules, and cell wall fragments. The extent of starch hydrolysis (%) after in vitro gastrointestinal digestion differs among whole navy beans (≈60 %) and milled bean flour (85–90%) due to differences in their microstructure. Intact cotyledon cells in the cooked whole navy beans provide resistance whereas disrupted cotyledon cells in bean flour allow proper gelatinization and enzymatic digestion of starch. The cotyledon cell structure of the cooked whole navy beans is maintained quite well throughout the in vitro gastric and small intestinal digestion period. The storage of freshly cooked beans reduces the starch hydrolysis levels due to retrogradation.