Abstract
The immune system provides host protection to infection with pathogenic organisms, while at the same time providing tolerance upon exposure to harmless antigens. Thus, an impaired immune function is associated with increased susceptibility to infections with increased disease severity and thereby necessitating the therapeutic use of antibiotics. Livestock performance and feed efficiency, in addition to their health status, are dependent on the microbial load of their gut, the barrier function of the intestinal epithelium and the activity of the mucosal immune system, all of which can be modulated by dietary components. The majority of feeds that are consumed in pets and livestock have been processed. Processing promotes a non-enzymatic reaction between proteins and sugars called Maillard reaction (MR). Maillard reaction products (MRPs) and advanced Maillard reaction products (AGEs) determine taste, smell, and color of many food products therefore the MR is highly relevant for the feed industry. MRPs interact with different types of immune receptors, including the receptor for advanced glycation end products (RAGE) and immunomodulatory potential of feed proteins can be modified by Maillard reaction. This MR has become an important concern since MRPs/AGEs have been shown to contribute to increasing prevalence of diet-related chronic inflammatory states in the gut with negative health consequences and performance. The immunomodulatory effects of dietary MRPs and AGEs in livestock and pet animals are far less well-described, but widely considered to be similar to the relevant concepts and mechanisms obtained in the human field. This review will highlight immunological mechanisms underlying initiation of the innate and adaptive immune responses by MRPs/AGEs present in animal feeds, which are currently not completely understood. Bridging this knowledge gap, and taking advantage of progress in the human field, will significantly improve nutritional quality of feed and increase the prevention of diet-mediated inflammation in animals.
Highlights
Protein Quality of Animal FeedsDietary proteins are a source of amino acids and the ability to absorb amino acids and use them for protein synthesis determines their quality and their required dose to meet the requirement [1]
The proportion of reactive lysine is on average, 73% of total lysine, while foods for growing dogs may supply less lysine content than the animals require and is recommended
On average and on a dry matter basis, higher Maillard reaction products (MRPs) and advanced glycation end products (AGEs) amounts occur in canned foods than in pelleted and extruded foods. van Rooijen et al [112] calculated that the content of CML and HMF that are present in commercial pet foods are, on average, within the range reported in processed human food products
Summary
Dietary proteins are a source of amino acids and the ability to absorb amino acids and use them for protein synthesis determines their quality and their required dose to meet the requirement [1]. Proteins are essential in foods, for its nutritional value, but they determine food structure, perception, and immunomodulatory capacity These functional characteristics are dependent on physico-chemical conditions like pH, ionic strength, temperature, or pressure, and the individual behavior of protein and their amino acids are largely unknown and unpredictable. Amino acids contained within the dietary protein can undergo crosslinking and glycation reactions, including the “Maillard reaction” (MR) or glycation, which is named after the French physician and chemist, Louis Camile Maillard, who in 1912 described this reaction for the first time [4]. The MR is known as the non-enzymatic browning reaction and typically involves amino acids (e.g., lysine, arginine) and reducing sugars (e.g., fructose, glucose) that progresses via a series of chemical rearrangements resulting in the formation of MR products (MRPs). In contrast to high molecular weight melanoidins, low molecular weight non-absorbed melanoidins are degraded in the intestines [10]
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