Classification of the spoilage flora of raw and pasteurized bovine milk, with special reference toPseudomonasandBacillus

摘要

Eighty‐one bacterial strains isolated from refrigerated raw milk, 124 from pasteurized milk and cream stored at 5°C and 7°C, and 19 type and reference strains ofPseudomonasspp. andBacillusspp. were characterized by numerical phenotypic analysis. Data were processed with simple matching (SSM) and Jaccard (SJ) coefficients, and UPGMA clustering. Fourteen clusters of Gram‐negative bacteria were formed atSJ= 79 (SSM= 90). Raw milk was exclusively spoilt by Gram‐negative bacteria, the majority of which werePseudomonas fluorescensbiovar I,Ps. fragi, Ps. lundensisandPs. fluorescensbiovar III. Minor groups in raw milk included Enterobacteriaceae spp. andAcinetobacterspp. Pasteurized milk was spoilt by essentially the same Gram‐negative organisms in 65 (5°C) and 50 (7°C) of the cases. The phenotypic characteristics of Gram‐negative bacteria are given.Bacillus polymyxa(both temperatures) andB. cereus(only at 7°C) were responsible for 77 of samples spoiled by the Gram‐positive organisms. Minor milk spoilage groups included otherBacillusspp. and lactic acid bacteria. AllBacillusspp. grew fermentatively in milk, and most strains denitrified. It is suggested that: (i) industrial recontamination tests of pasteurized milk are directed againstPseudomonas;(ii) milk is stored at 5°C or lower to avoid growth ofB. cereus; and (iii) the significance of gas‐producing and nitrate/nitrite‐reducingBacillusstrains is recognized