## 1 Introduction  
Cow's milk is a staple in many diets around the world, but the potential health effects of milk proteins remain a matter of debate, especially those related to the consumption of \(\beta\)-casein A1 and A2 variants. There are thirteen genetic variants of \(\beta\)-casein, but A1 and A2 are the most common [1]. Caseins comprise 80% of the protein in cow's milk, and \(\beta\)-casein represents about 22% of the total casein [2]. The A1 and A2 variants have attracted attention in the health field because of their potential implications in various diseases [3, 4, 5]. The only difference between A1 and A2 \(\beta\)-caseins is a single amino acid at position 67 of the protein chain: A1 has histidine, whereas A2 has proline [4]. This single substitution has significant consequences for digestion and physiological effects. The presence of histidine in A1 makes it susceptible to enzymatic cleavage during digestion, releasing a peptide called \(\beta\)-cascomorphin-7 (\(\beta\)CM-7). The proline in A2 prevents \"sterically hinders\" cleavage, so \(\beta\)CM-7 is released in much smaller amounts, probably minimal or barely noticeable ones [4; 6]. While food processing does not change one variant into another, certain processing methods can influence the release of these peptides into the processed food or during digestion in the intestine. For example, the curdling and aging processes in cheesemaking can alter the structure of casein. Cross-linking and other modifications cause individual casein molecules to no longer be in equilibrium with the micelle. The transport of intact molecules through the gut may therefore be prevented or hindered [7]. However, in [PERSON] et al. 's study, \(\beta\)CM-7 concentrations were higher in the A1A1 cheeses after pressing and during ripening [8]. Standard processes applied to milk, such as heat treatment and homogenization, although they can affect the overall structure of milk proteins, such as \(\beta\)-lactoglobulin denaturation and complex formation, do not appear to influence \(\beta\)CM-7 release [9]. In 2009, the European Food Safety Authority (EFSA) concluded that there is no direct link between \(\beta\)CM-7 and non-communicable diseases like cardiovascular conditions, autism, or insulin-dependent diabetes [10]. But \(\beta\)CM-7 is an opioid peptide with moderate agonist activity at the \(\mu\)4 receptors [11; 12]. This means that it can have morphine-like effects in the body. It has been suggested that \(\beta\)CM-7 may be associated with several health problems, which has led to a growing interest in the consumption of A2 dairy products, which are marketed as a healthier alternative [13]. One hypothesis suggests that \(\beta\)CM-7's presence in the gut triggers the activation of opioid receptors, potentially disrupting the balance of intestinal microbiota. This imbalance may compromise the integrity of the intestinal barrier and interfere with the bile acid metabolism, leading to additional effects. Recent research has increasingly focused on the gut-brain axis as a key pathway mediating the effects of dietary peptides such as \(\beta\)CM-7 [14]. Animal studies have been instrumental in understanding the health effects of A1 and A2 \(\beta\)-caseins, allowing a controlled analysis of their effects on various biological systems [15]. The main findings of these studies are that \(\beta\)-casein A1 has been associated with delayed gastrointestinal transit in rodents, whereas A2 appears to facilitate faster digestion. This effect may be due to the release of \(\beta\)CM-7 during A1 digestion, which can affect intestinal motility [3]. A1 has also been associated with an increase in the activity of myeloperoxidase, a marker of inflammation, in the rat intestine. This finding suggests that A1 may contribute to intestinal inflammation, a factor implicated in several digestive diseases [16]. In mice, feeding A1 was associated with an increase in leukocyte infiltration and the production of interleukin-4 and immunoglobulin E, indicators of an inflammatory response.