## 3 Results and Discussion
### Antioxidant and Radical Scavenging Activities of Cow Yogurts with Different Fat Content
To confirm the relation of proteins to the antioxidant activities, the pHAP extracts of the cow yogurts with different fat content were analyzed for their protein and total sulfhydryl groups concentration (Table 10). As indicated by both Lowry and Bradford assays, protein content of the three extracts followed the order 0% > 2% > 4% fat. The same order was observed for total sulfhydryl groups. content followed the same order. During the preparation of yogurt pHAP extract a large amount of proteins are precipitated and removed. Consequently, present results indicate that yogurt pHAP extracts contain more soluble peptides/proteins and also peptides/proteins containing sulfhydryl groups in the order 0% > 2% > 4%. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **\% Fat** \\ **of Yogurt** \\ \end{tabular} } & \multicolumn{3}{c}{**Hydroxyl Radicals**} & \multicolumn{3}{c}{**Superoxide Radicals**} \\  & **(mg Trolox/kg Yogurt)** & & **(mg Trolox/kg Yogurt)** \\ \cline{2-5}  & **pHAP Extract** & **CR Preparation** & **pHAP Extract** & **CR Preparation** \\ \hline
0 & 46.2 \({}^{\text{aA}}\)\(\pm\) 1.1 & 118.5 \({}^{\text{aB}}\)\(\pm\) 3.1 & 154.3 \({}^{\text{aA}}\)\(\pm\) 2.2 & 323.3 \({}^{\text{aB}}\)\(\pm\) 15.3 \\
2 & 36.7 \({}^{\text{bA}}\)\(\pm\) 0.8 & 98.9 \({}^{\text{bB}}\)\(\pm\) 2.2 & 137.8 \({}^{\text{bA}}\)\(\pm\) 1.7 & 244.1 \({}^{\text{bB}}\)\(\pm\) 15.2 \\
4 & 27.5 \({}^{\text{cA}}\)\(\pm\) 0.9 & 76.3 \({}^{\text{cB}}\)\(\pm\) 4.2 & 120.6 \({}^{\text{cA}}\)\(\pm\) 1.8 & 174.9 \({}^{\text{cB}}\)\(\pm\) 15.2 \\ \hline \hline \end{tabular} \({}^{\text{1}}\) Each value was expressed as mean \(\pm\) standard deviation of three replicates. Different lowercase letters in the same column represent significant differences in values (\(p\) < 0.05) between cow yogurts with different fat content. Different capital letters in the same row represent significant differences in values (\(p\) < 0.05) between pHAP and CR preparations of the same yogurt.  
\end{table} 
Table 9: Hydroxyl and superoxide anion radical scavenging activities of cow yogurts with different fat content preparations obtained by pH adjustment and precipitation (pHAP) and “Clarifying Reagent” (CR) \({}^{1}\). Protein and total sulfhydryl groupscontent of three yogurt pHAP extracts are consistent with their antioxidant and scavenging capacities reported above. This is logical as it is known that yogurt peptides exhibit antioxidant activities, while the -SH group can be oxidized to -S-S- exhibiting antioxidant activities. Analytical results of full-fat cow, goat and ewe yogurts as well as of cow yogurts with different fat content led to some general observations. In both Folin and FRAP assays, UC extracts of all yogurts examined exhibited higher antioxidant activities than the respective pHAP extracts. This can be attributed to materials that are precipitated and removed during the double pH adjustment (pH 4.0 and pH 7.0) applied in the procedure, such as proteinaceous materials [17; 20]. Moreover, CR preparations of all the yogurts exhibited much higher antioxidant scavenging capacities than the respective aqueous yogurt extracts. This is associated with the fact that \"Clarifying Reagent\" for dairy products dissolves both proteins and lipids, indicating that the latter may contribute to antioxidant and radical scavenging capacities of yogurt [21; 22]. Finally, DPPH, Folin and FRAP antioxidant assays showed analogous results in the evaluation of all yogurt extracts examined. It is logical as these three assays are based on a single electron transfer mechanism [28].