Percorrer por autor "Castro, M. H."
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- Death kinetics of Lactobacillus bulgaricus in a spray drying processPublication . Teixeira, Paula; Castro, M. H.; Kirby, R. MSurvival of Lactobacillus bulgaricus during spray drying was studied at various outlet air temperatures. During spray drying the logarithmic survival ratio decreased with increased outlet air temperature with first-order kinetics; the pseudo-z value for Lactobacillus bulgaricus was 17.3°C. Plots of the death-rate constant for Lactobacillus bulgaricus versus reciprocal outlet temperature during spray drying in skim milk show a curve with two different activation energies (Ea). The calculated Ea values were 33.47 kJ/mol above 70°C and 85.77 kJ/mol below 70°C. Thermodynamic quantities for spray drying of Lactobacillus bulgaricus are also presented. Results show that the relationship between the entropy of activation and the enthalpy of activation for both spray drying and heating in liquid medium is linear, with all the data for drying falling in the range of a negative entropy.
- Survival of Lactobacillus delbrueckii ssp. bulgaricus Following Spray-DryingPublication . Teixeira, Paula; Castro, M. H.; Malcata, F. X.; Kirby, R. MSurvival of cell concentrates of Lactobacillus delbrueckii ssp. bulgaricus following spray-drying in skim milk with and without ascorbic acid and monosodium glutamate was evaluated during storage at different conditions of temperature and water activity. High temperature and high water activities were detrimental to survival of dried cells. The death rate was higher in the presence of ascorbic acid and monosodium glutamate during storage at 20°C; at 4°C. survival was higher in the presence of these agents. The developed sensitivity of survivors to chemical inhibitors with specific action was used to provide insight into the nature of cellular damage. After drying, cells showed sensitivity to NaCl, lysozyme, penicillin, and pyronin Y, indicating damage to the cell membrane, cell wall, and DNA, respectively.