Browsing by Author "Carvalho, A. Sofia"
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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.
- Relationship between solubility of freeze-dried skim milk and death of freeze-dried Lactobacillus delbrueckii ssp. bulgaricus during storagePublication . Carvalho, A. Sofia; Silva, Joana; Ho, P.; Teixeira, Paula; Malcata, F. X.; Gibbs, P.To elucidate the relationship between death of freeze-dried cells of Lactobacillus bulgaricus during storage and decrease in powder solubility, the effect of milk precipitation during rehydration of freeze-dried Lb. delbrueckiissp. bulgaricus upon death of these cells throughout storage, via addition of various carbohydrates to the drying medium was studied. The degree of survival of freeze-dried Lb. bulgaricus was found to be directly proportional to the square root of the absorbance of the supernatant. A darker powder resulted when most of the microorganism had died. A tentative explanation for the insolubility observed when the viability of the cells decreased is based on an increase in the extent of non-enzymatic browning (Maillard reactions), as a result of cell death. Results obtained throughout this study might represent a helpful tool towards development of a novel, straightforward, shortcut method for monitoring the viability of freeze-dried samples during storage
- Survival of freeze-dried Lactobacillus plantarum and LactobacillusPublication . Carvalho, A. Sofia; Silva, Joana; Ho, Peter; Teixeira, Paula; Malcata, F. Xavier; Gibbs, PaulNo significant differences were observed in the viability of Lactobacillus plantarum and Lactobacillus rhamnosus cells during freeze-drying in the presence or absence of inositol, sorbitol, fructose, trehalose, monosodium glutamate and propyl gallate. However, survival was higher during storage when drying took place in the presence of these compounds. Sorbitol produced more significant effects than the other compounds toward maintaining viability of freeze-dried L. plantarum and L. rhamnosus.