# Evaluation of In Vitro Antihypertensive and Anti-Inflammatory Properties of Dairy By-Products
## 3 Results and Discussion
### Determination of ACE-Inhibitory Activity of Dairy By-Products
In our study, no significant differences in ACE-inhibitory activity between D-P3 and D-P10 were evident for both SW and YAW. Although this seems to not be in line with what has been previously reported, it should be taken into consideration that, while in the abovementioned studies, non-overlapping fractions are compared, in our procedure, the D-P10 fraction contains all peptides that are present in the D-P3 fraction. This suggests that peptides with MW below 3 kDa are mainly responsible for the ACE-inhibitory effect also observed in the D-P10 fraction. Furthermore, it is worth noting that the reported differences in ACE-inhibitory activity between studies may be a result of different digestion procedure and enzymes, as well as different food matrices tested and initial protein concentration. Regarding the animal origin effect, although there are several reports dealing with dairy proteins on several species, there are no available comparative studies between species. [PERSON] et al. [39] reported that the ACE-inhibitory activity of camel milk and camel colostral whey was enhanced after in vitro digestion, suggesting that ACE-inhibitory peptides corresponding to camel milk and colostrum, respectively, were released. [PERSON] reported that the ACE-inhibitory activity of skimmed caprine milk at the end of in vitro gastrointestinal digestion was lower than that observed after gastric digestion. Those results suggested that the ACE-inhibitory activity of caprine milk hydrolysates decreased as the length of the peptides decreased, and further degradation resulted in a decrease in ACE-inhibitory activity [40]. [PERSON] et al. [41] evaluated the ACE-inhibitory activity of bovine, ovine, and caprine \(\kappa\)-casein macropeptides (CMPs) and their tryptic hydrolysates. The results exhibited an increase in ACE-inhibitory activity after in vitro digestion for all three CMPs, without, however, having been compared with each other regarding the different animal origin. The beneficial effects of dairy fermented foods on health can be more correctly assessed when tested following in vitro digestion, as bioactive peptides that are contained in larger peptides are thus released. In a study comparing ACE-inhibitory activity after fermentation combined with in vitro digestion of milk whey protein to pea protein, [PERSON] et al. [42]suggested that in vitro digestion is the dominant factor controlling ACE inhibition, closely resembling the in vivo condition. However, the hydrolysis of bioactive peptides into inactive fragments during digestion is sometimes likely to occur [43]. [PERSON] et al. [44] observed a significant interaction regarding ACE-inhibitory activity between the molecular mass of Asiago d'allevo semi-hard cheese and gastrointestinal digestion. This interaction results from a decreased ACE-inhibitory activity in <3 kDa fraction and an increased activity in <10 kDa fraction after digestion. It should be noted however that in this study, fractions were produced from water-soluble extracts of cheese samples before in vitro digestion and are therefore not representative of an actual food component. In our study, in vitro digestion was performed on raw materials (SW and YAW) that contained a variety of peptides regarding their molecular mass and the observed increased ACE-inhibitory following in vitro digestion is in accordance with the observed results of [PERSON] et al. for the <10 kDa fraction. Similarly, [PERSON] et al. reported that simulated gastrointestinal digestion had a positive effect (5-fold increase) on the ACE-inhibitory activity of a yak and cow hard, fermented dairy product, chhunpi [43]. This increase is notably higher than the one reported by us. This can be attributed to the higher percentage of caseins in cheese, which are almost absent in YAW [45] and very low in SW [46; 47], mainly in the form of caseinomacropeptide [48], as well as the possible higher initial activity of our SW and YAW samples compared to the cheese samples.