## 2 Antidiabetic Agents  
One of the body enzymes involved in the regulation of the glucose level is DPP4 [15]. This enzyme is involved in the incretin effect after meal consumption. Increting, like glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are hormones that decrease blood glucose levels by stimulating insulin secretion and inhibiting glucagon release. GIP serves several additional functions including promotion of growth and survival of the pancreatic beta-cell and stimulation of adipogenesis [15]. This effect is hindered by DPP4, therefore inhibition of DPP4 prolongs the incretin effect and lowers the postprandial blood glucose level (Figure 2) [16]. [PERSON] et al. [17] identified DPP4 inhibitory peptides in water-soluble Gouda cheese extracts. Peptides derived from \(\beta\)-casein (LPQNIPPL) and \(\alpha_{\text{S1}}\)-, \(\alpha_{\text{S2}}\)-, \(\beta\)-caseins (LPQ) evoked the highest DPP4-inhibiting effect in vitro. Their IC\({}_{50}\) values were 46.0 and 56.7 \(\upmu\)M, respectively. The bioactivity of the LPQNIPPL sequence was also tested on rats (Female Sprague Dawley, 8-week-old). The administration of this peptide at 300 mg \(\times\) kg\({}^{-1}\) body weight reduced significantly the postprandial glucose level in those rats [16]. Other peptides with DPP4 inhibitory bioactivity that were identified in Gouda cheese water-soluble-extracts (WSE) were characterized with the following sequences: VPITPL (110 \(\upmu\)M), VPITPT (130 \(\upmu\)M), FPGPIPN (260 \(\upmu\)M), YFPGPIPN (670 \(\upmu\)M), PGPHNS (1000 \(\upmu\)M), IPPLTQTPV (1300 \(\upmu\)M), PQNIPPL (1500 \(\upmu\)M), and VPFFIQPE (2500 \(\upmu\)M). Their activity expressed in IC\({}_{50}\) values was provided in brackets [17]. Antidiabetic properties of peptides may also result from their ability to inhibit \(\alpha\)-glucosidase (EC 3.2.1.20). \(\alpha\)-Glucosidase is an enzyme located in the brush border of enterocytes of the jejunum in the small intestine and is a key enzyme in carbohydrate breakdown. It cleaves carbohydrate to easy absorbable glucose. Thus, one of the T2D preventive strategies is to decrease the postprandial hyperglycemia by delaying glucose absorption through the inhibition of \(\alpha\)-glucosidase (Figure 3). \(\alpha\)-Glucosidase inhibitors also play a crucial role in the secretion of GLP-1 in healthy and diabetic patients, due to the prolonged incretin effect [18]. \(\alpha\)-Amylase is another enzyme involved in the regulation of the blood sugar level [5]. This enzyme is responsible for the initial hydrolysis of the \(\alpha\)-D-(1-4) glycosidic bonds of polysaccharides like glycogen  
Figure 2: The involvement of the dipeptidyl peptidase IV inhibitors in prolonging the incretin effect according to [PERSON] [16]. and starch to oligosaccharidesadarides. Then, oligosaccharidesad are further hydrolyzed into monosaccharidesadides by \(\alpha\)-glucosidaseae (see above), which are next transferred into bloodstream [5]. Some milk proteins were reported as the sources of \(\alpha\)-glucosidaseae inhibitors. Whe proteins: \(\alpha\)-lactalbumin, \(\beta\)-lactoglobulin, serum albumin, and lactoferrin hydrolysate obtained by peptic digestion were confirmed to exert such an inhibiting effect. \(\beta\)-Lactoglobulin and whey protein isolate hydrolysates were found to inhibit \(\alpha\)-glucosidaseae (IC\({}_{50}\) value of 3.5 and 4.5 mg \(\times\) mL\({}^{-1}\), respectively) [18]. Dipeptide, like arginine-proline (RP), derived from whey proteins and being the component of commercial Pep2 Dia(r) product, affected the inhibition of \(\alpha\)-glucosidase with an IC\({}_{50}\) value of \(0.0025\,\text{mg}\times\text{mL}^{-1}\)[19]. To the best of our knowledge, there is no research papers about \(\alpha\)-amylase inhibitors identified milk proteins and dairy products. Only one article concerned cheese as a source of \(\alpha\)-glucosidase inhibitors. According to [PERSON] et al. [20], Prato cheese inhibited \(\alpha\)-glucosidase activity in vitro by 52.6%.