###### Abstract
Additionally, the decrease in cell viability during the passage through the gastrointestinal (GI) tract is not taken into consideration [9]. Recent advances in gastrointestinal simulation techniques have made it possible to better understand the dynamic interactions that influence the survival and activity of probiotics along their journey through the digestive tract. The limited survival of probiotics during in vitro digestion is a complex process that is influenced by many factors, including the acidity of the stomach, the presence of bile salts and enzymes, the gut microbiota and its colonization resistance, and the properties of the probiotic strain itself [10]. The acidic environment of the stomach is one of the most significant challenges to the survival of probiotics. To survive the acidic environment of the stomach, probiotics must have some protective mechanisms in place. These mechanisms include the production of acids and enzymes that can neutralize stomach acid [11], the formation of protective biofilms [12; 13], and the ability to adhere to the stomach lining [14]. Bile salts and enzymes are also major challenges to the survival of probiotics. Bile salts are produced by the liver and are released into the small intestine. Bile salts have many antimicrobial properties that can kill probiotic bacteria [15]. Antimicrobial proteins are also present in the small intestine and act as a defense mechanism against external micro-organisms [16]. To survive the bile salts and enzymes, bacteria must have the ability to adhere to the intestinal lining and to produce protective substances (bile salt hydrolase) that can neutralize the bile salts [17]. In addition to the acidity of the stomach and the presence of bile salts and enzymes, the physical and chemical properties of the probiotic strain also play a role in its survival during in vitro digestion. Probiotic strains that are more resistant to acidity, bile salts, and enzymes are more likely to survive the in vitro digestion process. Additionally, probiotic strains that can adhere to the intestinal lining and produce protective substances are also more likely to survive the in vitro digestion process [18]. Coating is also one of the strategies utilized to improve the survival of probiotics during digestion and to improve the shelf life of the product [19]. Different functional materials can be used as coating substances to tackle various challenges expected during the oral delivery of probiotics [20]. Polysaccharides, such as alginate, as well as cellulose and lipid-based coating, are commonly used to protect the probiotics from low pH of the gastrointestinal tract. Coatings can also be utilized to supply the probiotic cells with prebiotics by using inulin or polydextrose as coating material. Additionally, coating can improve the intestinal retention by strengthening the interaction between probiotics and the intestinal mucus layer. Composite biomagnetic materials can be utilized in the coating layer to improve both the retention and cellular localization of the probiotics [21]. Also, natural ingredients such as red ginseng dietary fiber can improve the intestinal adhesion of probiotics [22]. The first section of the paper discusses the mechanisms underlying the survival of probiotic LAB during in vitro digestion, which is especially important for the evaluation of possible probiotics since only living bacteria can fully confer their health benefits after successfully passing through the GI tract [23]. The acidic environment of the stomach and the presence of bile salts and enzymes pose significant challenges to the viability of these micro-organisms. For the in vitro digestion, we have chosen samples that were cultured in stress conditions (of high temperature and pH shock) that contained freshly cultured bacteria, and dried and coated preparations, as well as preparations after storage, to check their influence on the survival of probiotic bacteria during the gastrointestinal passage.