# Impact of Lactic Acid Bacteria on Immunoreactivity of Oat Beers
## 1 Introduction
It is also suggested to use selected cultures of lactic acid bacteria as fermentation starters as a way to eliminate the risk of gluten contamination. An innovative approach is to support the digestion of toxic sequences already in the gastrointestinal tract through oral administration of enzyme preparations or by shaping the composition of the intestinal microbiome with the desired metabolic abilities [21; 29; 31]. So far, none of these solutions is completely satisfactory, but they all aim to effectively eliminate toxic proteins. An alternative may be to combine several of the above methods. The beer production process itself is associated with a significant reduction in protein content in the product. Both during the malting and mashing stages, the digestion of proteins occurs as a result of the activity of proteolytic enzymes [32]. The mashing process includes a proteolytic rest step at temperatures optimal for protease activity (45-55 \({}^{\circ}\)C) to enhance protein degradation. By selecting processing conditions such as malt grind size, temperature, and time, the protein hydrolysis process can be effectively regulated [33]. As a result, only part of the proteins in a soluble form forms the word extract, because a significant portion of the proteins forms sediments and is separated from the word during filtration. This precipitation occurs as the temperature is progressively raised from the initial 45 \({}^{\circ}\)C [32]. The mashing process is often enhanced by the use of commercially available proteases [32]. This strategy is behind the technologies already implemented on an industrial scale for the production of gluten-free beers from barley. The production of gluten-removed barley beer is based on protein hydrolysis supported by the addition of exogenous enzymes. However, such solutions are still controversial, as there is a high risk that toxic amino acid sequences may remain in the product [34; 35]. Another way to support the degradation of gluten peptides in brewing could be the use of lactic acid bacteria. The potential of lactic acid bacteria (LAB) to minimize the immunological response by hydrolyzing alpha-gliadin fragments and reducing the level of gluten is currently often listed as a promising strategy in combating gluten intolerance [21]. The proteolytic mechanism of lactic acid bacteria comprises extracellular and cell wall-associated proteases, which cleave proteins into oligopeptides that are transferred across the cell membrane, and several intracellular peptidases that may contribute to gluten degradation. Highly variable peptidase activity has been observed in different strains (i.e., iminopeptidase, aminopeptidase N, prolidase, prolyl endopeptidyl peptidase, prolinase, tripeptidase, and dipeptidase) [31]. A way to reduce the level of toxic peptides in beer may be the hydrolysis of peptide bonds by LAB used at the malting stage [36; 37; 38]. The introduction of lactic acid bacteria into malt production is a solution already known in brewing. Lactic acid bacteria are a group of microorganisms naturally occurring on the surface of the grain. The use of LAB starter cultures in the process of malting is primarily intended to reduce the development of unfavorable microbiota. It also improves the technological parameters of so-called sour malls and the quality of the resultant beers [39; 40; 41; 42]. An additional advantage could be the reduction of the risk of unintentional ingestion of toxic gluten by hypersensitive individuals. This beneficial effect may be due to the fact that some bacteria synthesize peptidases capable of degrading immunoreactive peptides [37; 43; 44; 45; 46]. Numerous studies confirm the ability of lactobacilli to hydrolyze gluten proteins, reducing their toxicity and inflammatory effect in the intestines [31]. The aim of this study was to compare the immunoreactivity of oat and barley beers and examine the effect of lactic fermentation on reducing immunoreactivity as a result of the proteolytic activity of LAB towards proline-rich peptides.