Tracking new functionalities of whey proteins: structural impact of dry heating treatments at alkaline conditions

Whey is a protein-rich coproduct of dairy industry that has gained space on food industry and academic research at the past recent years. It contains globular proteins (mainly β-lactoglobulin-βlg and α-lactalbumin-αla), lactose, minerals and residues of fat. Besides their nutritional value, whey protein isolate (WPI), is a valuable ingredient, also, because of its technological properties. Processes like heating treatments, may result in structural modifications of proteins and, consequently, in changes on their techno-functional properties. Dry heating is an innovative technology that consists on heating powders, allowing controlled Maillard reaction. In this study, commercial WPI (94% of protein) with and without added lactose was rehydrated, pH adjusted to 7 and 9 and then lyophilized. Powders (water activity lower than 0,1) were dry-heated at 60 and 80°C for 48 hours and then analyzed according to protein structure. Results show reduction on lactose amount and increment of browning indexes as long as the temperature of treatment rise, indicating consumption of the reducing sugar by Maillard reaction. The alkaline pH resulted in a reduction of solubility even at non heated samples, this insoluble material presented a water holding capacity of yield up to 2,4g of wet pellet per g of powder. Soluble phase and the pellet have been analyzed by SDS-PAGE that revealed the presence of soluble aggregates of αla only for samples treated at 80°C. βlg, on the other hand, showed more aggregation in soluble and insoluble phases, given by its higher reactivity. Size-exclusion chromatography showed increment of about to 400% of high molecular weight aggregates on soluble phase of added lactose samples. This work surely provides useful information about how the emerging treatment affect protein structure and, consequently their properties.