Influence of preliminary incubation on the methylene blue results of farm-refrigerated milks

Abstract

Samples of raw refrigerated milk were analysed bacteriologically for total bacterial, coliform, psychrophilic, casein digester, and thermoduric counts initially, and after storage overnight at 50°, 60° and 70°F. The combination of methylene blue reduction and nitrate reduction tests after preliminary incubation of the sample for 24 hr at 60°F effectively eliminated milks of poor bacteriological quality. However, for practical purposes it is suggested that a methylene blue reduction test of 3 hr after such pre-incubation would give a good assessment of initial bacterial flora and would seem to be the most satisfactory standard for Queensland milk supplies.