Comparative study of in vitro digestibility and antioxidant activities of whey from different milks

Whey proteins, a protein-rich by-product of milk, contribute to various biological benefits. These bioactivities play an important role in human health and can be enhanced when whey proteins are digested, yet the digestion of whey proteins from different animal species under standardized protocols of in vitro digestion and its effect on antioxidant activity remain insufficiently characterized. This work aims to compare the digestibility and antioxidant activities of whey from the milk of different animal species: cameline, bovine, ovine, caprine, and equine.

Milk samples from the five species were coagulated to obtain whey. The whey proteins were digested with pepsin and pancreatin in an in vitro process that mimics digestion in the gastrointestinal tract. Physicochemical parameters, protein profiles (SDS‑PAGE), peptide concentration, degree of hydrolysis (DH), and antioxidant activities were analyzed to assess inter‑species differences.

After milk coagulation, a slight increase in pH values was observed in all whey samples. The maximum peptide concentration was observed in the digested ewe whey, while digested mare whey showed the lowest. Camel whey has the highest content of sodium, potassium, zinc and iron, while goat whey has the highest concentration of copper and ewe whey has the highest concentration of calcium. The SDS-PAGE profiles showed that all five milk types had an identical protein profile, with the exception of camel whey, which was characterised by the absence of β-lactoglobulin (β-Lg) and the presence of two different proteins camel whey basic protein (CWBP) and Peptidoglycan recognition protein (PGRP). The highest antioxidant activity was found in ewe whey. The sensitivity of whey proteins to hydrolysis varies between milk types. Correlation analysis indicated that the DH was significantly positively correlated with peptide concentrations (r = 0.998, p < 0.0001), indicating that increased proteolysis facilitates peptide liberation. Simulated gastrointestinal digestion produced peptides exhibiting antioxidant properties across all five species, reinforcing the notion that whey hydrolysates offer a valuable avenue for enhancing this by-product.

These findings highlight the nutritional and functional diversity of whey proteins among animal species. Hydrolysates of whey proteins from all animal species studied could be an interesting approach to add value to this by-product.