Survival and growth of Salmonella and Vibrio in som-fak, a Thai low-salt garlic containing fermented fish product
Fermentation of raw fish is a common process in Asia for improvement of shelf life and safety, however, little is known about the survival of pathogenic bacteria in these products. Raw fish may be contaminated with Salmonella and Vibrio species. The purpose of this study was to determine survival an...
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Veröffentlicht in: | International journal of food microbiology 2009-09, Vol.134 (3), p.223-229 |
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Zusammenfassung: | Fermentation of raw fish is a common process in Asia for improvement of shelf life and safety, however, little is known about the survival of pathogenic bacteria in these products. Raw fish may be contaminated with
Salmonella and
Vibrio species. The purpose of this study was to determine survival and potential growth of
Salmonella enterica serovar Weltevreden,
S. enterica serovar Enteritidis,
Vibrio cholerae and
V. parahaemolyticus as influenced by the preservation parameters (sodium chloride, garlic and lactic acid) present in the Thai fermented fish product
som-fak. The inhibitory effects of sodium chloride (0–4%), garlic (0–10%) and lactic acid (pH levels as in
som-fak) were measured in modified brain heart infusion (BHI) broth at 30 °C. All bacteria were inhibited by 8–10% sodium chloride.
Salmonella grew in all concentrations of garlic whereas
Vibrio spp. were inhibited by 1.0–1.5%. Lactic acid was inhibitory at levels above 1.5%. The combinations of sodium chloride, lactic acid and garlic showed a distinct hurdle effect in the broth system. Neither
S. Enteritidis,
V. cholerae nor
V. parahaemolyticus grew in garlic (0.5–1%), regardless of the level of sodium chloride (0.5–4% (w/v)), when lactic acid (0.5–2%) was present.
S. Weltevreden was the least inhibited of the four bacteria and grew in the combination of 0.5% garlic and 0.5% lactic acid regardless of the NaCl level (0.5–4% (w/v)).
Som-fak with 0 to 10% garlic or 2% glucose was inoculated with either (i) 10
3 CFU/g
Salmonella Weltevreden, (ii) 10
6 CFU/g garlic fermenting
Lactobacillus plantarum strain 509 or (iii) a combination of the two strains and stored at 30 °C. The
Salmonella count increased to >
10
8 CFU/g (>
10
6 CFU/g for 10% garlic) in all types of
som-fak inoculated with
S. Weltevreden within the first day. Only a combination of at least 6% garlic and
L. plantarum 509 was enough to prevent growth of the inoculated
Salmonella whereas adding the
Lactobacillus strain alone or in combination with glucose was insufficient to prevent growth. Our results show that
Salmonella Weltevreden can grow in
som-fak independently of the inhibitory substances normally present in this type of product, emphasising the importance of preventing contamination. However, our results also suggest that the use of garlic fermenting starter cultures in combination with garlic could improve safety of fermented fish products. |
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ISSN: | 0168-1605 1879-3460 |
DOI: | 10.1016/j.ijfoodmicro.2009.06.012 |