Protein‐added kefir: biochemical changes in in vitro digestion stages

Abstract BACKGROUND While yogurt is the leading fermented milk product, kefir is at the top of the beverage scale. Milk proteins, on the other hand, show specific functions that positively affect healthy nutrition due to the bioactive components, that they provide the necessary amino acids for growth and development. RESULTS In our study, kefir, a functional product enriched with whey proteins, casein and skimmed milk powder, which are the natural components of milk, was produced. Added‐protein kefir samples were applied the in vitro digestion protocol, static method. In order to observe different protein behaviors, samples were taken pre‐digestion, at 120th minute and at 240th minute of digestion protocol. ACE and Antioxidant capacity determination analyzes were carried out. While ACE inhibition values were in the range of 78.63–90.30% pre‐digestion, they changed in the range of 86.97–96.38% after gastrointestinal digestion. It was determined that the ACE inhibition values of the control sample remained at the lowest level at all stages of digestion and that the difference between all of samples was significant ( P < 0.05). Antioxidant activity value ranging from 0.3615–0.5512 meq Ascorbic acid/μg before digestion was determined as 1.3796–1.9313 meq Ascorbic acid/μg after gastrointestinal digestion ( P < 0.05). CONCLUSION Kefir samples containing whey protein stand out with their high potential in terms of both antioxidant activity capacity and ACE inhibition activity at all stages of digestion. Considering their therapeutic effects in fermented products, it is thought that whey proteins among milk proteins will be important alternative sources to enrich the protein content in kefir production. © 2024 Society of Chemical Industry.