Heat induced aggregation of whey proteins is affected by storage conditions of WPI powders
Résumé
Supported by high added value products, the market of dairy protein powders has shown a continuous increase over the past decade. During powder manufacture, precautionary measures are taken to ensure optimal technological and nutritional functionalities regarding their use requirements. However, changes in physico-chemical and functional properties of whey protein isolates (WPI) powders appear during storage, which is not as well mastered as previous processing. It is therefore of high interest to understand the mechanisms and identify the structural markers involved in WPI powders ageing in order to control their end use properties. This study was performed to determine the effects of different storage conditions applied to WPI powders on heat induced aggregation of whey proteins, and simultaneously on both protein denaturation and lactosylation. Therefore, two different storage conditions regarding temperature (20 and 40 °C) have been carried out for periods of up to 15 months. On the one hand, our results showed that protein lactosylation occurred in WPI powders at 20 °C, but heat induced aggregation did not significantly differ from non-aged whey protein isolates. On the other hand, powders presented a high level of denaturation and aggregation at 40 °C, involving first protein lactosylation and then aggregation in the dry state. These evolutions were correlated with an increasing Browning Index starting from the first month of storage, and with a decrease in aggregate size after heat treatment at pH ≥ 5.8. A change in the shapes of heat induced aggregates was concomitantly observed. These results pave the route for a better control of functional properties of WPI powders during ageing, and for recommendations about optimal storage conditions.