Can operational parameters impact spray-dried bacteria viability and production costs? An experimental study with...

Lactococcus lactis subsp. lactis Q1C2, previously isolated from artisanal cheese produced in the Brazilian Amazon region, was subjected to spray drying protocols to evaluate the impact of operational parameters on cell viability, storage stability, and production costs. Concentrated reconstituted milk was used as the drying medium, and combinations of cell concentrate flow rates (F_cell,inj) and inlet air temperatures (T°C_air,in) were tested, resulting in 12 different treatments (T1-T12). After drying (day-0), higher survival rates were obtained with lower T°C_air,in (115 °C and 130 °C), while greater viability loss was associated with higher T°C_air,in and outlet air temperatures (T°C_air,out). Moisture content and water activity (a_w) were inversely correlated with cell viability, with lower values resulting in greater losses. Cell viability was evaluated during the storage at 4 °C and 25 °C on days 15, 30, and 120. Viability was more stable at 4 °C, although significant reductions were observed for some treatments (P < 0.0001). At 25 °C, all treatments exhibited significant viability losses after 120 days (P < 0.0001). Among the treatments, T6 (F_cell,inj = 0.66 kg h^-1 and T°C_air,in = 130 °C) showed the best balance between high cell viability and storage temperature, 10.00 ± 0.12 log cfu g^-1 and 9.93 ± 0.13 log cfu g^-1 after 120 days at 4 °C and 25 °C, respectively. In terms of production costs, T6 demonstrated advantages by minimizing energy consumption and mass loss during drying. Higher F_cell,inj reduced energy costs (P < 0.0001), while elevated T°C_air,in significantly increased energy costs (P < 0.0001). T6 optimized energy efficiency and achieved a favorable balance between viability and operational costs, highlighting its potential for industrial application. These findings demonstrate the viability of spray drying for producing dairy starter cultures, offering a cost-effective solution to preserve active starter cultures without the need for refrigeration.