Institute of Food, Nutrition and Human Health, Massey University, Private Bag 11222, Palmerston North, New Zealand.
Int J Food Microbiol. 2013 May 15;163(2-3):129-35. doi: 10.1016/j.ijfoodmicro.2013.02.009. Epub 2013 Feb 28.
Bacteria in raw milk can produce heat-stable lipases, which survive pasteurisation and subsequently reduce the shelf life of dairy products because of their ability to break down the milk fat and increase rancidity. In this study, four bacteria, originating from the surfaces of raw milk transport tankers, and a known lipase-producing bacterium were evaluated for their ability to produce lipolysis in planktonic and biofilm cultures. Lipolysis was determined using two separate assays that measured hydrolysis of the ester p-nitrophenol palmitate (pnpp) and the lipid tributyrin. The hydrolysis of pnpp per CFU within biofilms and planktonic cultures ranged from 0.01 to 8.35 and 0.01 to 0.07 nU/CFU respectively. The amount of butyric acid released from hydrolysis of tributyrin per CFU within biofilms and planktonic cultures ranged from 0.1 to 1110.3 and 0.1 to 0.3 ng/CFU, respectively. The hydrolysis of pnpp and tributyrin per CFU within biofilms was at least 10 times higher compared with the corresponding planktonic cultures. This is the first study to show that lipolysis occurs within biofilms of bacteria that were originally isolated from the surfaces of raw milk tankers. This is relevant to the dairy industry, highlighting the importance of eliminating biofilms on milk tanker surfaces as a source of heat-stable lipases.
生奶中的细菌会产生热稳定脂肪酶，这种酶可以在巴氏杀菌后存活下来，并由于其分解乳脂和增加酸败的能力，从而缩短乳制品的保质期。在这项研究中，从生奶运输罐表面分离出的四种细菌和一种已知的产脂酶细菌，评估了它们在浮游生物和生物膜培养物中产脂酶的能力。脂解作用通过两种独立的测定来确定，这两种测定分别测量酯 p-硝基苯酚棕榈酸酯（pnpp）和脂质三丁酸酯的水解。生物膜和浮游生物培养物中每个 CFU 的 pnpp 水解量分别为 0.01 至 8.35 和 0.01 至 0.07 nU/CFU。生物膜和浮游生物培养物中每个 CFU 从三丁酸酯水解产生的丁酸量分别为 0.1 至 1110.3 和 0.1 至 0.3 ng/CFU。生物膜中每个 CFU 的 pnpp 和三丁酸酯水解量至少比相应的浮游生物培养物高出 10 倍。这是首次表明脂解作用发生在最初从生奶罐表面分离的细菌生物膜中的研究。这与乳制品行业相关，强调了消除牛奶罐表面生物膜作为热稳定脂肪酶来源的重要性。
