Intact cells: “Nutritional capsules” in plant foods

Abstract

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.

Intrinsic dietary fibers and the gut microbiome: Rediscovering the benefits of the plant cell matrix for human health

“…To these backbones other sugar molecules and also phenolic acids can be linked, such as the hemicellulose type arabinoxylan ( 56 , 57 ). Finally, pectin serves like a filler giving the cellulose-hemicellulose scaffold stability, controlling permeability and together creating a matrix that can retain water ( Figure 1A ) ( 55 , 58 ). Similarly to hemicellulose, also pectin is a group of structurally diverse polymers, which have a linear galacturonic acid backbone (homogalacturonans) or a galacturonic acid and rhamnose backbone (rhamnogalacturonans) that can be further decorated with side-chains forming complexly branched polymers ( Figure 1A ) ( 20 , 24 , 59 ).…”

“…While all plants share these common aspects of the plant cell wall, their make-up differs depending on the type of plant (e.g. monocots versus dicots; see below), its maturation or ripeness and especially food processing ( 18 , 52 , 58 ). Even within plants, differences in cell types exist between the tissue we consume (such as leaf, root, fruit, stem, seed) and within these tissues ( 52 , 56 ).…”

“…As hemicellulose and pectin are groups of very heterogenous polymers, the specific types of these fibers that are present in the plant cell walls distinguish different plant types ( 52 , 58 ). Vegetables, fruits, nuts, seeds and legumes belong to the dicots, that have so-called type I cell walls, while grains are monocots having type II cell walls.…”

“…Type I cell walls of dicots contain xyloglucan as the most abundant hemicellulose and the hemi-/cellulose network is further stabilized by pectin, which has been reported to make up a third of the cell wall weight ( 18 , 52 ). In contrast type II cell walls of monocots, have no or very low amounts of pectin and the abundant hemicelluloses are β-glucan and arabinoxylan ( 52 , 58 ). Rice is one of the grains that contains some pectin, while oats and barley are particularly rich in β-glucan, and wheat, maize and rye in arabinoxylan ( 57 ).…”

“…contain by definition intrinsic fibers. However, any form of processing - industrial as well as domestic - can alter this three-dimensional structure ( 19 , 24 , 52 , 58 , 61 , 62 ) and whether a fiber is still an intrinsic fiber needs careful checking of the applied methodology.…”