Temperature-pressure-time combinations for the generation of common bean microstructures with different starch susceptibilities to hydrolysis

Abstract

In common beans, starch is enclosed by natural (micro)structural barriers influencing its behaviour during processing and digestion. Such barriers and their process-induced modifications could modulate nutrient delivery if adequate processing variables could be selected. In this study, the potential of different processing variables for generating common bean microstructures with different susceptibilities to in vitro starch hydrolysis was assessed. A traditional thermal treatment (95°C, 0.1MPa) and two alternative treatments including high hydrostatic pressure at room temperature (25°C, 600MPa) and at high temperature (95°C, 600MPa) were applied to common beans following a kinetic approach. (Micro)structural properties of (mechanically disintegrated) common beans were evaluated at each processing time. Mostly free, non-swollen and birefringent starch granules were obtained after mechanical disintegration of samples subjected to high pressure at room temperature. In mechanically disintegrated samples obtained by processes involving high temperature, either in combination with high pressure or not, there was major presence of cell clusters at early processing times (7–15min) and individual cells at intermediate and long times (≥45min). Following, specific process-induced common bean microstructures were evaluated in terms of in vitro starch hydrolysis kinetics. Rate constants of all microstructures obtained after high temperature treatments were similar, whereas final values of digested starch and initial reaction rates exhibited differences. The variations observed in the later parameters were correlated with the starch bio-encapsulation degree. Furthermore, in samples with the same starch bio-encapsulation degree (individual cells), differences in final digested starch and initial reaction rate were hypothesised to originate from differences in cell wall porosity/fragility.