Intact cells: “Nutritional capsules” in plant foods

Macronutrients of pulses or cereals are stored in the cotyledon or endosperm cells with protection from intact cell walls. However, pulses and cereals are generally processed into fine particles during food production. For example, after milling, the macronutrients enclosed in the intact cells are released and are easily accessible to digestive enzymes in the gastrointestinal tract, leading to high metabolic responses. Therefore, studies on the health effects of intact cells and developing an alternative ingredient with a higher proportion of intact cells are areas of emerging interest. In this review, we highlighted the smallest unit of whole grain, an individual cell, as "nutritional capsules" and elucidated the structure-function of the nutritional capsules, followed by isolation techniques, as a potential novel functional ingredient and food. The polysaccharides' monomeric composition, secondary structure, and interactions determine the cell wall properties including the cell detachment during isolation and isolated cell properties. The intact cellular structure is retained after mild food processing and digestion, thereby, contributing to a lower extent/rate of digestion of entrapped macronutrients. Furthermore, the excursed intact capsules in the colonic environment modulate the population and diversity of microbiota, favouring the increased production of the short-chain fatty acids (SCFAs). The structural schematic model of Type-I and Type-II cells is developed together with the schematics of the cell wall isolation process. The review provides a critical summary of the recent trends in intact plant cells as a functional-nutritional food. It paves the way for the industrial production of intact cells as a novel food ingredient.