The Survival of Lactococcus lactis in a Convective-Air-Drying Environment: The Role of Protectant Solids, Oxygen Injury, and Mechanism of Protection

The effect of protectant solids (lactose, sodium caseinate, and their mixture) on the survival of Lactococcus lactis subsp. cremoris was studied in a convective-air-drying environment using single droplet drying. The effect of drying the bacteria in the presence or absence of sodium ascorbate was evaluated, and the evolution of glass transition temperature in the drying process was examined. It was found that the protective efficiency of lactose and sodium caseinate was comparable at the concentrations tested. A mixed protectant matrix (lactose:sodium caseinate, 3:1) gave higher survival than with lactose or sodium caseinate alone at the same total solids level. Protectants enhanced bacterial survival by moderating the drying rate and achieving dryness at lower temperatures, and by facilitating the formation of a glassy matrix earlier in the drying process. The addition of sodium ascorbate was also examined.