## 4 Discussion

Table 4: Comparison of the number of biologically active peptides (BAPs) sequences generated by the tested strains of _Lb. heleticus_. different levels of protein hydrolysis carried out by the tested strains (different enzymatic specificity of bacterial proteases as well as different effectiveness and extent of the proteolysis process). Similar observations were reported by [PERSON] et al. [56], who also noted that proteolytic activity toward whey proteins was dependent on the strain of bacteria. The lower values of the hardness parameter noted in the variants of beverages containing _Lb. heleticus_ B734 is probably related to the specificity and activity of the proteolytic system of the strain. This is in agreement with findings described by [PERSON] et al. [57], who analyzed different bacterial cultures used in cheese production and revealed that the hardness values of fermented products (mainly related to the primary proteolysis, breakdown of both \(\alpha\)- and \(\beta\) fractions of casein) were substantially lower in fermented products obtained by addition of probiotic bacteria. Moreover, [PERSON] et al. [58] noted that samples of yoghurt obtained with the application of strains with low proteolytic activity exhibited more hardness than samples of the products received by using bacteria with strong proteolytic activity. This may suggest that _Lb. heleticus_ B734 exhibited higher activity towards the fermented matrix (RSM supplemented with WPI) referring to lower hardness value than the other tested strains (also for this reason, strain B734 was subjected to further analysis in the investigations). In addition, the obtained findings may also be associated with the fact that different peptides (with different amino acid sequences) were released from milk and whey proteins during fermentation via the enzymatic activity of different _Lb. heleticus_ strains, which probably influenced the structure of the gel network, i.e., a very dynamic system dependent on diverse interactions between the individual components (including milk proteins, denatured whey proteins, and calcium phosphate crosslinks) in the complex composition of fermented matrix [59]. It is also worth emphasizing that proteolysis processes (occurring also during lactic acid fermentation) not only lead to changes in the physical structure of the product but also contribute to the production of biopeptides [60; 61; 62]. Many BAPs derived from milk and whey proteins exhibit multiple bioactivities, bringing desired health-promoting effects, which contributes to the constantly increasing importance of the biopeptides and potential applications in pharmacy and medicine [63; 64; 60; 65; 34]. The desired therapeutic effects of BAPs extracted from milk and whey precursors have been confirmed, especially in terms of their ability to reduce blood pressure [63; 64; 65; 66; 67]. Our findings have revealed that a wide range of various BAPs can be obtained from 1% water solutions of WPI using strains of _Lb. heleticus_ (B734 and DSMZ 20075). The antihypertensive and ACE inhibitory effects were the predominant activities of the identified BAPs sequences. One of the thoroughly tested peptides with ACE inhibitory and antihypertensive activities (which was also detected in the WPI hydrolysate obtained with the use of _Lb. heleticus_ B734) is VPSERYL. It was revealed that this peptide at a concentration of 249.5 \(\upmu\)M inhibited 50% of the original ACE activity [36], whereas the value of 50% inhibitory concentration (IC\({}_{50}\)) for SQSKVLPVPQ (sequence released from WPI by the reference strain DSMZ 20075) was at the level of 92.00 \(\upmu\)M [44]. This peptide was also detected by [PERSON] et al. [61] in samples of WPI fermented with _Lb. heleticus_ LH-2 CFSM. Due to their influence on blood pressure and desirable cardiovascular effects, opioid peptides are other important sequences of BAPs generated from whey and milk proteins (mainly from \(\alpha\)-lactalbumin and \(\beta\)-lactoglobulins) [66].