Dry-Heating-Induced Microparticles of β-Lactoglobulin: Understanding the Respective Role of Alkaline pH and Lactose

When whey proteins are stored in solution at 4 °C and pH 9.5 in the presence of lactose and then dried, dry-heating (DH) of the powder at 100 °C leads to the formation of protein–protein cross-link within the powder particles. Suspensions of the dry-heated powder consist of microparticles with sizes similar to those of the original powder grains, which entrap large amounts of water for functional purposes. In this work, the denaturation and aggregation of pure β-lactoglobulin (β-Lg) and the yield of its conversion into microparticles were characterized at different stages of the process under different conditions (pH, presence of lactose, sucrose, and ammonium chloride) to gain insight into the mechanism of microparticle formation. Qualitatively, only limited changes in the secondary structure of β-Lg were shown during storage of β-Lg solution at pH 6.5 and 9.5. However, increased denaturation and aggregation with prolonged storage at pH 9.5 promoted microparticle formation. β-Lg aggregates formed during storage at pH 9.5 were precursors for their DH-induced cross-linking into microparticles in the presence of Maillard reaction products.