Bernbom Nete, Ng Yoke Yin, Paludan-Müller Christine, Gram Lone
DTU Aqua, National Institute of Aquatic Resources, Technical University of Denmark, Søltofts Plads, Building 221, 2800 Kgs. Lyngby, Denmark.
Int J Food Microbiol. 2009 Sep 15;134(3):223-9. doi: 10.1016/j.ijfoodmicro.2009.06.012. Epub 2009 Jul 6.
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 degrees 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 degrees 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.
生鱼发酵是亚洲一种常见的用于延长保质期和提高安全性的工艺，然而，对于这些产品中致病细菌的存活情况却知之甚少。生鱼可能被沙门氏菌和弧菌属污染。本研究的目的是确定泰国发酵鱼制品som-fak中存在的保存参数（氯化钠、大蒜和乳酸）对肠炎沙门氏菌韦尔泰弗里登血清型、肠炎沙门氏菌肠炎血清型、霍乱弧菌和副溶血性弧菌存活及潜在生长的影响。在30℃下，于改良脑心浸液（BHI）肉汤中测定了氯化钠（0 - 4%）、大蒜（0 - 10%）和乳酸（som-fak中的pH水平）的抑制作用。所有细菌均被8 - 10%的氯化钠抑制。沙门氏菌在所有浓度的大蒜中都能生长，而弧菌属被1.0 - 1.5%的大蒜抑制。乳酸在浓度高于1.5%时具有抑制作用。氯化钠、乳酸和大蒜的组合在肉汤系统中显示出明显的栅栏效应。当存在乳酸（0.5 - 2%）时，无论氯化钠水平如何（0.5 - 4%（w/v）），肠炎沙门氏菌、霍乱弧菌和副溶血性弧菌在大蒜（0.5 - 1%）中均不生长。韦尔泰弗里登沙门氏菌是这四种细菌中受抑制最少的，在0.5%大蒜和0.5%乳酸的组合中，无论氯化钠水平如何（0.5 - 4%（w/v））均能生长。将含有0至10%大蒜或2%葡萄糖的som-fak接种以下任意一种：（i）10³CFU/g韦尔泰弗里登沙门氏菌，（ii）10⁶CFU/g大蒜发酵植物乳杆菌菌株509，或（iii）两种菌株的组合，并在30℃下储存。在接种韦尔泰弗里登沙门氏菌的所有类型的som-fak中，沙门氏菌数量在第一天内增加至>10⁸CFU/g（10%大蒜时>10⁶CFU/g）。只有至少6%大蒜与植物乳杆菌509的组合足以防止接种的沙门氏菌生长，而单独添加乳酸杆菌菌株或与葡萄糖组合添加不足以防止生长。我们的结果表明，韦尔泰弗里登沙门氏菌能够在som-fak中生长，而不受这类产品中通常存在的抑制物质的影响，这突出了防止污染的重要性。然而，我们的结果也表明，使用大蒜发酵起始培养物与大蒜相结合可以提高发酵鱼制品的安全性。
