Effect of cell integrity on soybean protein digestion and fermentation: an in vitro study

Plant foods are organized into hierarchical structures that range in scale from centimeter dimensions of plant tissue to the nanometre scale of intracellular macronutrients (starch, lipid, and protein) inside plant cells. This natural encapsulation system may restrict the access of digestive enzymes to macronutrients during gastrointestinal digestion, particularly when the integrity of plant cell walls is preserved after food processing. A better understanding of the triangular relationship between plant food structure, food processing, and food digestion is of great importance and it is essential for designing and developing the strategies that could help to improve plant protein digestibility and utilization by the human body.In this thesis, we have used soybean particles and intact cells as plant food models to elucidate the effect of cell wall integrity on plant protein digestion and colonic fermentation. Initially, different particle sizes of raw and boiled soybean (as whole cotyledon or flour) were compared for their protein digestibility and cellular integrity. The data showed that decreasing particle size and increasing the proportion of cell rupturing increases the digestibility of protein contained within soybean particles. The cellular integrity of particles was observed by the use of confocal microscopy. The microscopy images showed that the proportion of ruptured cells within particles having the same size was greater for particles prepared from soybean boiled as flour compared to the particles prepared from soybean boiled as a whole cotyledon or raw soybean flour. This data gave insights into the fate of cell wall integrity during food processing procedures (milling before or after boiling) and the influence of cellular integrity of soybean particles in modulating protein digestibility. To investigate the individual contribution of the cell wall of intact cells in modulating protein digestibility, isolated intact cells were digested and the results ind