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 (T g ) rather than drying technology. When storage temperature approached T g , 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 T g .