Loading...
5 results
Search Results
Now showing 1 - 5 of 5
- 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.
- Partial characterization of nine bacteriocins produced by lactic acid bacteria isolated from cold-smoked salmon with activity against listeria monocytogenesPublication . Tomé, Elisabetta; Todorov, Svetoslav D.; Gibbs, Paul A.; Teixeira, Paula C.Nine LAB bacteriocin-producers, isolated from vacuum-packaged cold-smoked salmon (CSS), were phenotypically and genotypically identified as Lactobacillus curvatus, Lactobacillus delbrueckii, Lactobacillus fermentum, Enterococcus faecium, and Pediococcus acidilactici. Their bacteriocins were partially characterized. The antimicrobial spectrum was determined against Listeria monocytogenes, E. faecalis, E. faecium, and Staphylococcus aureus. The molecular size of bacteriocins ranged from 2.8 to 4.5 kDa. They were inactivated by treatment with proteolytic enzymes but not by lipolytic or glycolytic enzymes. Maximal activity against L. monocytogenes ranged between 800 and 10000 AU/mL at pH 6.5. Most of the bacteriocins maintained full activity in a pH range of 2.0 to 8.0 but were partially or completely inactivated at pH 10.0. After heating at 60°C and 100°C, only two bacteriocins from Lb. curvatus strains partially lost activity. All bacteriocins showed a narrow spectrum of activity and a high anti-listerial activity, which is characteristic of the class IIa bacteriocins. Isolated bacteriocinproducing LAB could be used successfully in the bio-preservation of CSS and development of new potential bio-preservatives for CSS active against L. monocytogenes.
- 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.
- Anti-listerial inhibitory lactic acid bacteria isolated from commercial cold smoked salmonPublication . Tome, Elisabetta; Teixeira, Paula; Gibbs, Paul A.The natural microflora of cold-smoked fish at the end of shelf-life are lactic acid bacteria (LAB). Some of these display a capacity to inhibit spoilage as well as several strains of pathogenic micro-organisms, e.g. Listeria monocytogenes which is isolated frequently from cold-smoked salmon (CSS). Eight batches of sliced vacuum-packed CSS from Norway, Scotland and Spain were collected at retail. Packs were stored at 5 1C and examined for chemical and microbiological characteristics, at purchase date and at expiration date. pH, water activity and salt content were similar to available data on lightly preserved fish products. There was a consistent pattern in the development of the microflora on CSS; the initial level of LAB was low on freshly produced CSS (102 cfu g 1); however, storage in vacuum packaging at refrigeration temperature was elective for LAB. At the end of the stated shelf-life these micro-organisms, represented mainly by Lactobacillus spp., attained ca.107 cfu g 1 while Enterobacteriaceae counts were consistently lower (105 cfu g 1), which indicates the ability of LAB to grow and compete with few carbohydrates available and in the presence of moderate salt concentrations. L. monocytogenes was not found in any sample. Forty-one percent of LAB strains isolated exhibited inhibitory capacity against Listeria innocua, in a plate assay. A majority of the inhibitory effects were non-bacteriocinogenic, but nevertheless were very competitive cultures which may provide an additional hurdle for improved preservation by natural means. r 2005 Elsevier Ltd. All rights reserved.
- Growth control of listeria innocua 2030c on vacuum-packaged cold-smoked salmon by lactic acid bacteriaPublication . Tomé, Elisabetta; Gibbs, Paul A.; Teixeira, Paula C.Five bacteriocin-producing lactic acid bacteria (LAB): Enterococcus faecium ET05, Lactobacillus curvatus ET06, L. curvatus ET30, L. deldrueckii ET32 and Pediococcus acidilactici ET34, selected by their capacity for growth and producing inhibition in vitro at high salt-on-water content, low temperature and anaerobic atmosphere, conditions simulating cold-smoked fish,were inoculated onto salmon fillets, in co-culturewith Listeria innocua 2030c, and cold-smoked processed (dry salted for 6h; drying for 6h; smoke for 2h).The finished product was then packed under vacuum and stored at 5 °C. Enumeration of LAB and L. innocua was performed during storage. Results showed that strain E. faecium ET05 was the best biopreservative candidate for controlling L. innocua growth in vacuum-packaged cold-smoked salmon (CSS) processed under the salting/drying/smoking parameters referred above. L. curvatus ET30 and L. delbrueckii ET32 also showed a good biopreservation potential for CSS although they were less effective than the former. L. curvatus ET06 and P. acidilactici ET34 showed a bacteriostatic mode of action against the target bacteria in vitro as well as when inoculated into the salmon fillets. This study describes a potential application of five different LAB in the biopreservation of Listeria in CSS.