Electrostatic spray drying of whey protein-carbohydrate systems: Influence of pH, water activity, and storage temperature on Maillard reactions

Maillard reactions continue during storage of dairy powders, but controlling mechanisms in low-moisture systems remain unclear. This study investigated whether drying technology directly determines reaction progression or acts indirectly by establishing the matrix's physicochemical state. Whey protein-carbohydrate solutions (lactose or lactose-glucose mixtures, pH 6.0 or 8.0) were freeze-dried or spray-dried (electrostatic or conventional) to defined water activities, stored at 20 or 40 °C and Maillard markers monitored. Differences observed immediately after drying reflected pre-vitrification reactions, with greater early-stage reactions in conventional spray drying. During storage, reaction progression depended mainly on the relationship between storage temperature and glass transition temperature (Tg) rather than drying technology. When storage temperature approached Tg, molecular mobility increased and glucose reactivity dominated, while initial pH had little influence. Overall, observations indicate a mobility-limited reaction regime post-matrix vitrification. Post-drying, Maillard markers reflected the influence of pre-vitrification reactions, whereas storage changes depended primarily storage temperature relative to Tg.