Modelling of heat and water transport in plantain during steeping to predict gelatinization and in vitro starch digestibility

A better understanding of starch-process interactions is the key point to better control banana starch digestibility and degree of cooking. This study aims at investigating and modelling the evolution of both the degree of cooking and in vitro digestibility of plantain starch as a function of steeping conditions. A 2D-axial-symmetric model considering a single Harton plantain cylinder being steeped in water was developed and adjusted to experimental data collected at 25, 50, 75 and 100 °C. Experimental temperature distribution was well predicted, with a thermal diffusivity of 1.5 × 10−7 m2s−1. The model was also validated against degree of starch gelatinization kinetics obtained by DSC at 100 °C. Two modes of water transport were found, depending on the starch state. At 25 °C or high degree of starch gelatinization (α ≥ 0.38), molecular diffusion was observed with an apparent water diffusivity of 2.4 × 10−9 m2.s−1, which may be due to structural cellular effects. At 50 °C, capillary diffusion was observed due to gas desorption, with an apparent water diffusivity of 10 × 10−9 m2.s−1. Starch digestibility was governed by gelatinization process which strongly depends on heat transport. This approach could be used to identify some steeping conditions that modulate both banana starch digestibility and degree of starch gelatinization.