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This article reviews the in vitro digestion models developed to assess the stability of food allergens during digestion. It is hypothesised that food allergens must exhibit sufficient gastro-intestinal stability to reach the intestinal mucosa where absorption and sensitisation (development of atopy) can occur. The investigation of stability of proteins within the gastrointestinal tract may provide prospective testing for allergenicity and could be a significant and valid parameter that distinguishes food allergens from nonallergens. Systematic evaluation of the stability of food allergens that are active via the gastrointestinal tract is currently tested in traditional pepsin digestibility models. The human gastrointestinal tract however is very complex and this article points out the importance of using physiologically relevant in vitro digestion systems for evaluating digestibility of allergens. This would involve the simulation of the stomach/small intestine environment (multi-phase models) with sequential addition of digestive enzymes, surfactants such as phospholipids and bile salts under physiological conditions, as well as the consideration of the effect of the food matrices on the allergen digestion.

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Microvilli are conventionally regarded as an extension of the small intestinal absorptive surface, but they are also, as latterly discovered, a launching pad for brush border digestive enzymes. Recent work has demonstrated that motor elements of the microvillus cytoskeleton operate to displace the apical membrane toward the apex of the microvillus, where it vesiculates and is shed into the periapical space. Catalytically active brush border digestive enzymes remain incorporated within the membranes of these vesicles, which shifts the site of BB digestion from the surface of the enterocyte to the periapical space. This process enables nutrient hydrolysis to occur adjacent to the membrane in a pre-absorptive step. The characterization of BB digestive enzymes is influenced by the way in which these enzymes are anchored to the apical membranes of microvilli, their subsequent shedding in membrane vesicles, and their differing susceptibilities to cleavage from the component membranes. In addition, the presence of active intracellular components of these enzymes complicates their quantitative assay and the elucidation of their dynamics. This review summarizes the ontogeny and regulation of BB digestive enzymes and what is known of their kinetics and their action in the peripheral and axial regions of the small intestinal lumen.