Antioxidant activity of bovine alpha lactalbumin Maillard products and evaluation of their in vitro gastro-duodenal digestive proteolysis
Food processing offers various pathways to tailor food functionality and digestibility. This work sought to study the impact of thermally-induced Maillard reaction between bovine alpha-lactalbumin (α-la) and fructose or fructo-oligosacchrides on physicochemical properties, antioxidant capacity and in vitro digestive fate under simulated adult and infant conditions. Colloidal stability (measured by DLS) was decreased as a result of the Maillard glycation, while antioxidant capacity (determined by FRAP) and surface hydrophobicity (H0 measurements) were elevated. Semi-dynamic in vitro digestion of Maillard conjugates revealed a mixed trend as a result of postulated competing effects of glycation on α-la's susceptibility to proteolysis; steric hindrance accompanied by protein unfolding could hinder or promote the availability of enzymatic cleavage sites. Results also showed thermal processing altered the digestive breakdown profile of α-la under infant conditions contrary to negligible effects observed under adult conditions. Evaluation of the antioxidant capacity during digestion (via DPPH assay) revealed that adult digesta possessed increased antioxidant activity throughout the gastric phase compared to infant digesta, whereas infant digesta of conjugates exhibited an increase in antioxidant capacity in the duodenum compared to adult. Moreover, during infant digestion of conjugates, an increase in antioxidant capacity was observed in the later stages of the digestion. Overall, this work demonstrates that controlled thermal processing of bovine α-la could potentially modulate its functionality and digestibility, particularly as it pertains to its ability to interfere with oxidative reactions in the lumen, possibly through the generation of bioactive peptides.