Morandi Stefano, Pica Valentina, Masotti Fabio, Cattaneo Stefano, Brasca Milena, De Noni Ivano, Silvetti Tiziana
National Research Council, Institute of Sciences of Food Production, Via G. Celoria 2, 20133 Milan, Italy.
Department of Food, Environmental and Nutritional Sciences, Università degli Studi di Milano, Via G. Celoria 2, 20133 Milan, Italy.
Foods. 2021 Apr 24;10(5):934. doi: 10.3390/foods10050934.
The proteolytic traits of the psychrotrophic strains Pseudomonas poae LP5, Pseudomonas fluorescens LPF3, Chryseobacterium joostei LPR1, Pseudomonas fulva PS1, Citrobacter freundii PS37, Hafnia alvei PS46, and Serratia marcescens PS92 were initially investigated by phenotypic and genotypic approaches. Six strains elicited extracellular proteolytic activity, and five expressed the thermostable AprX or (likely) Ser1 enzymes. Then, the strains were inoculated (10 CFU/mL) in microfiltered pasteurized milk and kept at 4 °C for five days. All of the strains reached 10 CFU/mL at the end of storage and five produced thermostable extracellular proteolytic enzymes. The freshly inoculated samples and the corresponding samples at 10 CFU/mL were batch-sterilized (131 °C, 30 s) and kept at 45 °C up to 100 days. The former samples did not gel until the end of incubation, whereas the latter, containing , , , , and gelled within a few days of incubation. The thermostable proteolytic activity of strains affected the peptidomic profile, and specific proteolyzed zones of β-CN were recognized in the gelled samples. Overall, the results confirm some proteolytic traits of psychrotrophic Pseudomonas spp. strains and provide additional insights on the proteolytic activity of psychrotrophic bacteria potentially responsible for sterilized milk destabilization.
最初通过表型和基因型方法研究了嗜冷菌株波氏假单胞菌LP5、荧光假单胞菌LPF3、约氏金黄杆菌LPR1、微黄假单胞菌PS1、弗氏柠檬酸杆菌PS37、蜂房哈夫尼亚菌PS46和粘质沙雷氏菌PS92的蛋白水解特性。6株菌株产生细胞外蛋白水解活性，5株表达耐热的AprX或（可能）Ser1酶。然后，将这些菌株（10 CFU/mL）接种到微滤巴氏杀菌乳中，并在4℃下保存5天。储存结束时，所有菌株均达到10 CFU/mL，5株产生耐热的细胞外蛋白水解酶。将新鲜接种的样品和10 CFU/mL的相应样品进行间歇灭菌（131℃，30秒），并在45℃下保存100天。前一组样品直到培养结束才凝胶化，而后者，含有 、 、 、 和 的样品在培养几天后就凝胶化了。菌株的耐热蛋白水解活性影响了肽组图谱，并且在凝胶化样品中识别出了β-酪蛋白的特定蛋白水解区域。总体而言，结果证实了嗜冷假单胞菌属菌株的一些蛋白水解特性，并为可能导致灭菌乳不稳定的嗜冷细菌的蛋白水解活性提供了更多见解。
