Identification of proteolytic psychrotrophic bacteria isolated from refrigerated raw milk and characterization of its spoilage potential

Abstract

This study aimed to identify proteolytic psychrotrophic bacteria isolated from refrigerated raw milk, to evaluate their spoilage potencial and their capability of adhesion to stainless steel surfaces at cold temperatures. Among gram-positive bacteria, 23.81% and 33.33% of isolates belonged to Bacillus and Paenibacillus genera. In the gram-negative glucose fermentative bacteria group, the genera Cedecea, Enterobacter, Hafnia, Klebsiella, Pantoea, Providencia, Rhanella and Serratia were identified, while the genera Acinetobacter, Aeromonas, Burkholderia, Chryseobacteriun (Flavobacterium), Chryseomonas, Moraxella and Pseudomonas were identified among gram-negative non fermentative microorganisms. The genus Pseudomonas, which was predominant, represented 33.98% of total isolates. Among fermenters of glucose bacteria, 14.6%, 15.3% and 20.8% of isolates showed predominantly proteolytic activity at 6.5, 21 and 35 ºC, respectively, while 25% e 23.6% of isolates belonging the gram-negative non-fermenting microorganisms showed associated activities of proteases, lipases and lecithinases at 6.5 and 21 ºC,respectively, emphasizing their greatest spoilage potential. Gram-positive and gram-negative bacteria produced heat resistant proteolytic enzymes and adhesion to stainless steel surfaces at 6.5 ºC. The results of this study reinforce the importance of the implementation of good manufacturing practices in order to prevent Milk spoilage and minimize economic and quality losses.