Identifcation of the contaminating psychrotrophic bacteria in refrigerated bulked raw milk and the assessment of their deteriorating potential Identifcação da microbiota psicrotrófca contaminante em leite cru refrigerado granelizado e avaliação do seu potencial deteriorador Patrícia Rodrigues Condé 1 ; Cláudia Lúcia de Oliveira Pinto 2 ; Scarlet Ohana Gandra 3 ; Renata Cristina Almeida Bianchini Campos 1 ; Roselir Ribeiro da Silva 4 ; Jhonatan Faria da Costa 5 ; Maurilio Lopes Martins 4 * Highlights Bacteria with greater spoiling potential produced lecithinase. In autumn there was a predominance of proteolytic bacteria at 4.0 °C. More than 80% of the isolates belonged to the Pseudomonas fuorescens species. Abstract This work aimed to characterize, identify, and determine the deteriorating potential of the contaminating psychrotrophic bacteria in refrigerated raw milk. Samples were submitted to serial dilutions and plated in specifc culture media to form a bacterial culture collection. The isolates were characterized for their morphology and biochemical characteristics. The deteriorating potential of the isolates was determined according to the proteolytic, lipolytic and lecithinase activities at 4.0 ºC, 6.5 ºC, and 25.0 ºC. The results obtained for deterioration potential were assessed by the multivariate statistical method and by the principal components analysis (PCA). A total of 159 isolates were characterized, and of these, 46 strongly proteolytic Gram-negative isolates were selected for identifcation using the API 20 NE kit. The predominant bacteria were Gram-negative and oxidase and catalase positive, with a predominance of bacteria of the genus Pseudomonas. Using PCA, it was shown that the bacteria with the greatest deterioration potential were lecithinase producers, and that, in the autumn, proteolytic bacteria predominated at 4.0 ºC. Of the 1 M.e, Professional Masters in Food Science and Technology, Instituto Federal do Sudeste de Minas Gerais, IF Sudeste MG, Rio Pomba, MG, Brazil. E-mail: patricia.conde@ifsudestemg.edu.br; renata.campos@ifsudestemg.edu.br 2 Dra, Agricultural Microbiology, Empresa de Pesquisa Agropecuária de Minas Gerais, EPAMIG, Viçosa, MG, Brazil. E-mail: claudia.epamig@gmail.com. 3 Food Science and Technology Student, IF Sudeste MG, Rio Pomba, MG, Brazil. E-mail: scarlet05jbgandra@gmail.com 4 Profs., Food Science and Technology Department, IF Sudeste MG, Rio Pomba, MG, Brazil. E-mail: roselir.silva@ ifsudestemg.edu.br; maurilio.martins@ifsudestemg.edu.br 5 M.e, Professional Master in Science and Technology of Milk and Dairy Products, Universidade Federal de Juiz de Fora, UFJF, Juiz de Fora, MG, Brazil. E-mail: jhonatan.faria@ifsudestemg.edu.br * Author for correspondence 739 Semina: Ciênc. Agrár. Londrina, v. 43, n. 2, p. 739-750, mar./abr. 2022 DOI: 10.5433/1679-0359.2022v43n2p739 Received: Aug. 11, 2021 - Approved: Dec. 09, 2021 ARTICLES / ARTIGOS