Debevere J, Devlieghere F, van Sprundel P, De Meulenaer B
University of Ghent, Department of Food Technology and Nutrition, Belgium.
Int J Food Microbiol. 2001 Aug 15;68(1-2):115-23. doi: 10.1016/s0168-1605(01)00484-6.
In this work, the TMAO-reduction by Shewanella baltica, one of the representative spoilage organisms in modified atmosphere packaged marine fish fillets, and the effect of acetate and CO2 on this reduction were studied in vitro. The growth of S. baltica and the corresponding evolution of some compounds (acetate, lactate, pyruvate, glucose and trimethylamine (TMA)) were followed during storage at 4 degrees C in two types of broths. The first medium was a defined medium (pH = 6.8) to which lactate or pyruvate was added as hydrogen donor. Pyruvate showed to be more efficient as H-donor for S. baltica than lactate, as growth was much faster when equimolar amounts of pyruvate instead of lactate were present. Although the growth of S. baltica, when pyruvate is used as H-donor and no acetate is added, was not much inhibited by the CO2-atmosphere, CO2 had a pronounced effect on the studied reactions as it partly inhibited the reduction of pyruvate to acetate. The effect of acetate on this reaction was, on the other hand, not significant. To simulate the reactions occurring in situ, a buffered fish extract (pH = 6.8) was used. In spite of the neutral pH, the growth of S. baltica in this medium was highly inhibited by relatively small concentrations of acetate (< 0.3%). When 0.1% of acetate was added to the fish extract, less acetate was formed and lactate was more slowly consumed in comparison to the experiments without the addition of acetate. The consumption of lactate and the production of acetate were almost completely inhibited when the fish extract contained 0.25% of acetate. Apparently, the addition of acetate inhibited the use of lactate as H-donor. After extended storage times (17 days at 4 degrees C) TMA production started. Most probably, alternative H-donors were used by S. baltica, from which the pathway seems to be less energy efficient. This can be deduced from the exceptional growth inhibition of S. baltica by small amounts of acetate. However, when practical storage times for fish (e.g. 6 days at 4 degrees C after packaging) are considered, growth and TMAO-reduction by S. baltica was completely inhibited during this period by 0.25% of acetate.
在这项研究中，我们在体外研究了波罗的海希瓦氏菌（一种气调包装海鱼片中典型的腐败菌）对氧化三甲胺（TMAO）的还原作用，以及乙酸盐和二氧化碳对该还原作用的影响。在两种肉汤中于4℃储存期间，监测了波罗的海希瓦氏菌的生长以及一些化合物（乙酸盐、乳酸盐、丙酮酸盐、葡萄糖和三甲胺（TMA））的相应变化。第一种培养基是一种特定培养基（pH = 6.8），向其中添加乳酸盐或丙酮酸盐作为氢供体。丙酮酸盐作为波罗的海希瓦氏菌的氢供体比乳酸盐更有效，因为当存在等摩尔量的丙酮酸盐而非乳酸盐时，生长速度要快得多。尽管当使用丙酮酸盐作为氢供体且不添加乙酸盐时，波罗的海希瓦氏菌的生长受二氧化碳气氛的抑制不大，但二氧化碳对所研究的反应有显著影响，因为它部分抑制了丙酮酸盐向乙酸盐的还原。另一方面，乙酸盐对该反应的影响不显著。为了模拟原位发生的反应，使用了一种缓冲鱼提取物（pH = 6.8）。尽管pH为中性，但在这种培养基中，相对低浓度的乙酸盐（< 0.3%）就能显著抑制波罗的海希瓦氏菌的生长。当向鱼提取物中添加0.1%的乙酸盐时，与未添加乙酸盐的实验相比，形成的乙酸盐减少，乳酸盐的消耗也更慢。当鱼提取物中含有0.25%的乙酸盐时，乳酸盐的消耗和乙酸盐的产生几乎完全受到抑制。显然，乙酸盐的添加抑制了乳酸盐作为氢供体的利用。在延长储存时间（4℃下17天）后，开始产生TMA。很可能，波罗的海希瓦氏菌使用了其他氢供体，而该途径似乎能量效率较低。这可以从少量乙酸盐对波罗的海希瓦氏菌异常的生长抑制中推断出来。然而，考虑到鱼的实际储存时间（例如包装后在4℃下6天），在此期间0.25%的乙酸盐完全抑制了波罗的海希瓦氏菌的生长和TMAO还原。
