## 4 Antioxidative Peptides  
Free radicals are involved in many signaling processes, i.e., as defending the body from infections. Thus, the accumulation of free radicals in the organism can lead to unwanted cell damage. Oxidized cells can then initiate several body dysfunctions like e.g., rapid ageing, atherosclerosis, arthritis, diabetes, and cancer (Figure 5). It is the so-called oxidative stress defined as the process of formation of highly reactive molecules (that is, reactive oxygen species-ROS). In order to act against the destructive activity of ROS, it is important to look for diet-derived compounds acting as antioxidants [42]. [PERSON] et al. [43] produced Cheddar cheese using different _Lactobacillus casei_ cultures and screened for antioxidant activity. Two antioxidative peptides matching the fragments of bovine \(\beta\)-casein  
Figure 5: The preventive activity of antioxidants on the formation of diseases according to [PERSON] and [PERSON] [42]. (VKEAMAPK) and \(\alpha_{\text{S1}}\)-casein (HIQKEDVPSER) were identified in Cheddar. Both peptides exhibited 2,2-diphenyl-1-picryl-hydrazyl (DPPPH) radical scavenging activity comparable to the commercial antioxidants such as butylated hydroxyanisole (BHA), _tert_-butyl hydroquinone (t-BHQ) or ferulic acid [44]. The results indicated that the antioxidant activity of the water-soluble cheese extracts (WSE) was dependent on the ripening period of cheese. The highest bioactivity was observed after 4 months of ripening. After that, the activity started to decrease, up until the 7 th month of ripening and remained similar after 9 months [44]. Another research group evaluated the inhibition of DPPH radicals by the WSE of Australian Cheddar cheeses. They found a moderate antioxidant activity of the fractions containing peptides with a molecular weight > 10 kDa, although peptide identification was not carried out [45]. A study conducted to analyze the antioxidative potential of Mexican Cotija cheese revealed that the maximal antioxidant activity of this cheese was achieved after 24 weeks of ripening. Although no specific peptides were identified, it was concluded that the antioxidative potential of cheese was related to a significantly high content of bioactive sequences [46]. [PERSON] et al. [47] produced hard cow cheese and analyzed the antioxidative potential of its WSE. After the fractionation of WSE, it was discovered that some of the extracts exhibited DPPH-radical scavenging and metal chelating bioactivity. Moreover, two peptides, namely EIVPN and DKIHPF which were known from their ACE-inhibiting function, were identified in WSE of the hard cheese. Another sequence i.e., VAPFPQ identified in cheese-derived extract was discovered as a new metal chelating peptide. To conclude, it was postulated that antioxidative potential of cheese water-soluble extracts may be the result of the presence of the above-mentioned peptides. However, the bioactivity of these sequences should be confirmed on synthetic peptides [47]. Some peptides with the antioxidative potential were identified in WSE of the Burgos-type cheese. It was shown that 22 fractions derived from Burgos-type cheese extracts exhibited radical scavenging activity (oxygen radical absorbance capacity with fluorescein (ORAC-FL) assay). Liquid chromatography and tandem mass spectrometry (LC-MS/MS) identification revealed the presence of the aromatic amino acids like tyrosine, phenylalanine or tryptophan in some fractions of cheeses extracts. These amino acids itself possess the antioxidative potential [48]. It was also reported that some of the Burgos-type cheese-originating peptide fractions contained the sequences, namely: SDIPNIGSENSEKTTMPLW (source: \(\alpha_{\text{S1}}\)-casein), YQQPVLGPVVRGPFPIIV (source: \(\beta\)-casein), and LLYQQPVLGPVRGFPIIV (source: \(\beta\)-casein) [49]. According to [PERSON] et al. [49], peptides matching the sequences of \(\beta\)-casein have already been known as antioxidative agents.