Psychrophilic organisms in Queensland butter

Abstract

Choice and first quality butters submitted for grading in Brisbane were examined for psychrophilic count at the same time as they were examined by the routine tests used in the Butter Improvement Service. Eighty-two per cent. of butters did not contain psychrophilic organisms in 1/10 g and only 7 per cent. contained more than 100 psychrophiles per g. However, one or more samples of butter from 25 of 35 factories sampled contained psychrophiles.
Although coliforms and psychrophilic organisms occurred as a result of post-pasteurization contamination, one type of contamination occurred frequently without the other. However, there was a general relationship between the two tests, as significantly larger numbers of coliform positive tests occurred in butters with higher psychrophilic counts.
The majority of the isolates were classified as Pseudomonas, with strains of Vibrio, Achromobacter, Aeromonas, Flavobacteriwn, Arthrobacter and Aerobacter also being found, as well as 2 yeasts. Over 90 per cent. of the isolates were lipolytic and over 70 per cent. proteolytic. When representative strains were inoculated into cream which was then made into butter, many produced serious flavour defects, including rabbito, rancidity, tallowiness or mouldy flavour.
Psychrophilic organisms isolated from 10 butters which had developed rabbito or rancidity were similar to many strains isolated from normal butters.