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- Impedimetric method for estimating the residual activity of freeze-dried Lactobacillus delbrueckii ssp. bulgaricusPublication . Carvalho, A. Sofia; Silva, Joana; Ho, Peter; Teixeira, Paula; Malcata, F. Xavier; Gibbs, PaulThe residual activity of Lactobacillus delbrueckii ssp. bulgaricus cultures was analysed using pH and various impedimetric methods (impedance detection time (IDT), conductance and capacitance) to quantify the loss in activity following freeze-drying. The large variation recorded in IDT values for similar levels of activity suggests that IDT is not an adequate parameter for estimating the culture's fermentative activity. Comparison of the impedance signals generated revealed that capacitance yields values that are more reproducible than those of conductance, and also gives a better correlation with pH. Statistical analysis (p<0.05) indicated that there are no significant differences between the capacitance and the pH method when attempting to estimate residual activity.
- Spray-drying for the production of dried culturesPublication . Silva, Joana; Freixo, Ricardo; Gibbs, Paul; Teixeira, PaulaThis review emphasises the importance of spray-drying as an under-used but promising technique to preserve viable and active starter cultures and also, potentially, probiotic cultures. The knowledge concerning the production of spray-dried starter cultures is discussed. Different drying techniques and micro-organisms have been investigated for their survival through the drying process. During drying and subsequent storage in the dried state, bacteria are subjected to several stresses, which have already been described as causing damage to cells, leading to the loss of cellular viability and activity. Some studies found that several factors ⁄ strategies can confer improved cellular viability.