# 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  
There is the notion that ACE-inhibiting potential is associated with low molecular weight peptides [35]. Thus, the ACE-inhibitory activity of SW and YAW was determined both before in vitro digestion and after digestion and fractionation. The results are shown in Figures 1 and 2. Figure 1: Effect of animal origin of sweet whey (SW) on angiotensin-converting enzyme (ACE)-inhibitory activity (%) before and after in vitro digestion. The vertical dashed lines separate the three different groups as follows: SW: sweet whey before digestion; SW-D-P10: digested fraction below 10 kDa after digestion; SW-D-P3: digested fraction below 3 kDa. Data are presented as means \(\pm\) SEM of three independent experiments. Columns with different letters significantly differ within the same group (\(p<0.05\)). * indicates a significant difference between two groups (\(p>0.05\)); ns indicates no significant difference between two groups (\(p>0.05\)). Figure 2: Effect of animal origin of yogurt acid whey (YAW) on angiotensin-converting enzyme (ACE)-inhibitory activity (%) before and after in vitro digestion. The vertical dashed lines separate the three different groups as follows: YAW: yogurt acid whey before digestion; YAW-D-P10: digested fraction below 10 kDa after digestion; YAW-D-P3: digested fraction below 3 kDa. Data are presented as means \(\pm\) SEM of three independent experiments. Columns with different letters significantly differ within the same group (\(p<0.05\)). * indicates a significant difference between two groups (\(p<0.05\)); ns indicates no significant difference between two groups (\(p>0.05\)). Figures 1 and 2 indicate that the ACE-inhibitory activity of SW and YAW, respectively, was significantly increased (\(p<0.05\)) after in vitro digestion, regardless of animal origin. Despite the increase in ACE-inhibitory activity after digestion (D-P10 and D-P3), no difference was observed between these fractions. The digestion process, therefore, had an overall positive effect on the ACE-inhibitory activity of SW and YAW. In Figure 1, the ACE% inhibition values of ovine SW were significantly higher (\(p<0.05\)) after digestion (D-P10 and D-P3) compared to the exprine and bovine counterparts. However, Figure 2 shows no statistically significant differences (\(p>0.05\)) in ACE-inhibition values between the YAW samples from different milk sources after digestion. Between the two by-products tested, SW displayed a higher ACE-inhibitory activity. This difference, which was consistent both before and after digestion, could be attributed to a variety of factors such as different raw material, protein content, structure of peptides, starter cultures used, etc. There is a strong consensus that peptides with low molecular weight possess stronger inhibitory activity against ACE, which partially explains our results for both by-products. Consistent with our results, [PERSON] et al. [36] reported that fractions with low molecular weight (<1 kDa and 1-3 kDa) of whey protein hydrolysate (WPH; 72% of protein was less than 10 kDa) displayed potent ACE-inhibitory activity compared to WPH. Also, a significant decrease in ACE-inhibitory activity for >5 kDa fraction compared to those of <1 kDa and 1-3 kDa fractions was reported [36]. Similarly, [PERSON] et al. [37] indicated that digested whey protein isolate (WPI) consisting of peptides < 3 kDa induced a greater ACE-inhibitory effect compared with undigested WPI, while no significant difference was observed between undigested WPI and >3 kDa fraction of digested WPI. Likewise, the permeate fraction < 1 kDa of bovine whey proteins (\(\alpha\)-lactalbumin and \(\beta\)-lactoglobulin) after hydrolysis, using a variety of different enzymes, had higher ACE-inhibitory potency than the corresponding reentate fractions [13]. [PERSON] et al. [38] observed a great ACE-inhibitory effect for the hydrolyzed whey protein concentrate (WPC) fraction < 3 kDa.