The Maillard Reaction (MR) is a non-enzymatic chemical reaction which results in the linkage between the amino group of amino acids and the carbonyl group of reduced sugars. MR products (MRPs) are common components of processed foods, mainly as a result of heating, especially in the Western diet. MRPs are classified as into three stages: initial, intermediate, and final stages, indicative of increased complexity and size, incurring different flavor, aroma, and texture. MRPs presence is known to reduce the nutritional quality of foods, particularly by reducing protein digestibility. Early reports have linked MRPs, especially advanced glycation end-products (AGEs) present in high concentration in the typical Western diet, to health conditions and diseases. However conflicting data has since been reported, and only a few (acrylamide, heterocyclic amines and 5-Hydroxymethylfurfural) MRPs have documented potential toxic or carcinogenic effects. High molecular weight MRPs are not available for direct absorption in the higher gastrointestinal tract, and are thus mostly metabolized by resident colonic microbes. MRPs have been the subject of sparse research interest in comparison with other non-digestible dietary elements. In this review, we outline the state of knowledge on MRPs in nutrition and health, and highlight the need to develop the limited knowledge on their impact on the gut microbiota and which metabolites derive from MRPs fermentation.

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Melanoidins are the final Maillard reaction products (protein–carbohydrate complexes) produced in food by prolonged and intense heating. We assessed the impact of the consumption of melanoidins from barley malts on gut microbiota. Seventy-five mice were assigned into five groups, where the control group consumed a non-melanoidin malt diet, and other groups received melanoidin-rich malts in increments of 25% up to 100% melanoidin malts. Feces were sampled at days 0, 1, 2, 3, 7, 14, and 21 and the microbiota was determined using V4 bacterial 16S rRNA amplicon sequencing and short-chain fatty acids (SCFA) by gas chromatography. Increased melanoidins was found to result in significantly divergent gut microbiota profiles and supported sustained SCFA production. The relative abundance of Dorea, Oscillibacter, and Alisitpes were decreased, while Lactobacillus, Parasutterella, Akkermansia, Bifidobacterium, and Barnesiella increased. Bifidobacterium spp. and Akkermansia spp. were significantly increased in mice consuming the highest melanoidin amounts, suggesting remarkable prebiotic potential.

Repeated oral exposure to CML limits dysbiosis in experimental colitis. IBD patients may modulate their microbiota profile by regulating the level and type of dietary MRP consumption.