School of Food and Advanced Technology, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand.
School of Food and Advanced Technology, Massey University (Albany), Auckland 0632, New Zealand.
Int J Food Microbiol. 2020 May 2;320:108543. doi: 10.1016/j.ijfoodmicro.2020.108543. Epub 2020 Jan 28.
This study investigated the effect of growth conditions on proteolytic activity of six Pseudomonas strains, (Pseudomonas fragi DZ1, Pseudomonas koreensis DZ138, Pseudomonas rhodesiae DZ351, Pseudomonas fluorescens DZ390, Pseudomonas synxantha DZ832 and Pseudomonas lundensis DZ845), isolated from raw milk. The proteolytic activity of all Pseudomonas strains in dairy media (skim milk and whole milk) was significantly higher (p < 0.05) than in non-dairy media (TSB), with most activity from Pseudomonas grown in whole milk. The proteolytic activity from P. lundensis DZ845 grown in TSB with the addition of 5% (w/v) butter was higher than other dairy ingredients added to TSB and the amount of proteolytic activity increased with increasing concentrations of butter (from 5 to 15%). P. rhodesiae DZ351 showed little proteolytic activity in all TSB supplemented with dairy ingredients. Only four of the six strains produced one protease of 47 kDa when grown in TSB. However, all six strains were able to produce at least one type of proteases in milk medium. For P. lundensis DZ845, a 12% casein zymography gel revealed that the presence of butter could induce proteolytic activity. This is the first study showing the effect of milk fat (butter) on the proteolytic activity of Pseudomonas. This highlights the greater vulnerability of whole milk compared to skim milk to proteolytic activity.
本研究考察了生长条件对 6 株假单胞菌（脆弱假单胞菌 DZ1、朝鲜假单胞菌 DZ138、罗得西亚假单胞菌 DZ351、荧光假单胞菌 DZ390、synxantha 假单胞菌 DZ832 和lundensis 假单胞菌 DZ845）的蛋白酶活性的影响，这些菌株均从生牛乳中分离得到。在乳基培养基（脱脂乳和全脂乳）中，所有假单胞菌的蛋白酶活性均显著高于非乳基培养基（TSB）（p < 0.05），其中在全脂乳中生长的假单胞菌活性最高。在添加了 5%（w/v）黄油的 TSB 中培养的 lundensis 假单胞菌 DZ845 的蛋白酶活性高于添加到 TSB 中的其他乳成分，并且随着黄油浓度的增加（从 5%到 15%），蛋白酶活性也随之增加。在添加了乳成分的所有 TSB 中，rhodesiae 假单胞菌 DZ351 的蛋白酶活性均较低。仅有 4 株菌株在 TSB 中培养时产生一种 47 kDa 的蛋白酶。然而，所有 6 株菌株均能够在乳基培养基中产生至少一种类型的蛋白酶。对于 lundensis 假单胞菌 DZ845，在含有 12%干酪素的凝胶电泳中显示，黄油的存在可以诱导蛋白酶活性。这是首次研究表明乳脂（黄油）对假单胞菌蛋白酶活性的影响。这突出表明全脂乳比脱脂乳更容易受到蛋白酶活性的影响。
