Studies on the discovery and function of antioxidants are consistently being performed because oxidative stress can cause various diseases. Many compounds and natural products have antioxidant activity in vitro; however, it is often difficult to reproduce their effects in vivo. Additionally, methods to measure antioxidant activities in cells are also scarce. Here, we investigated the antioxidant activity of milk proteins by observing the formation of arsenite‐induced stress granules as a tool to evaluate antioxidant activity in cells. Milk proteins not only decreased the formation of stress granules in several cell types but also scavenged 2,2'‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) radical cations in vitro. In addition, milk proteins inhibited cellular senescence based on an SA‐β‐galactosidase assay, and increased differentiation to myotubes from myoblasts isolated from the skeletal muscles of mouse pups. Taken together, our results demonstrate that milk proteins have an antiaging effect, especially prevention of skeletal muscle loss, through their antioxidant activities. Practical Application Our results provide that antioxidant effects of milk proteins containing α‐caseins, β‐caseins, and β‐lactoglobulin can mitigate aging‐related damage induced by oxidative stress through showing inhibition of cellular senescence and increase of differentiation and maturation of myoblast. Therefore, we suggest that milk proteins could be potent health supplements to prevent aging‐associated diseases, especially sarcopenia.

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