To evaluate the effect of supplementation of skim milk (SM) with Rosemary (Rosemarinus officinalis) water extract (RWE), the radical scavenging activity (RSA) using DPPH assay and total phenolic compounds (TPC) with Folin–Ciocalteau reagent were determined. Also, mixing periods and the total solids (TS) of the mixture were taken into consideration. Reducing the TS of reconstituted SM (3% to 0.35%) increased its RSA%, while its whey derivative showed high RSA% than its casein. RSA% of 10% RWE was 94%, it was high through the few min. of mixing and decreased upon elongated the mixing period until 60 min. Casein derivative showed the lowest value of RSA% and this value was not affected with mixing periods. Reducing the TS of SM—RWE mixture increased its RSA % at all mixing periods, whereas its casein derivative almost unaffected upon dilution its mixture.
Moreover, SM showed the highest TPC, reducing its TS decreased its TPC and also for its casein and whey derivatives. The TPC of RWE was 458mg / L gallic acid, reducing the concentration of RWE to 1.5 % decreased its TPC to 130 mg / L. gallic acid SM- RWE mixture had the highest content of PC after all mixing periods ( few min to 60 min ) for all TS conc. Conversely, its separated casein showed the lowest content of TPC, and diluted the mixture decreased the TPC of casein. This confirms that there was a part of antioxidant activity which masked by specific interactions between casein protein and rosemary phenolic compounds.
Furthermore, the correlation coefficient between RSA% and TPC of RWE was 0.992 and it was 0.990 and 0.884 for casein and whey derivatives respectively, while SM had negative correlation coefficient taking TS as a factor. There was a good correlation coefficient between RSA% and TPC for SM- RWE and its whey derivative through the few min. of mixing with reducing the TS of the mixture to 0.75 and 0.35 % SM-TS, whereas casein derivative had negative correlation coefficient at all different mixing periods and TS concentration of the mixture.