Incidence of spore-forming bacteria in unsweetened evaporated milk brands in Nigeria

Abstract

A total of forty-five samples of three most commonly consumed unsweetened evaporated milk brands purchased from retail outlets in South-western Nigeria were examined for occurrence of spore-forming bacteria. All the samples had high numbers of spore-forming bacteria of the genera Bacillus spp and Clostridium spp. with mean total aerobic viable counts of 2.15x105cfuml-1 for br and A, 0.95x105cfuml-1 for brand B and 0.69x105cfuml-1 for brand C. Total anaerobic plate counts ranged from 0.13x105 for
brand C, to 0.54x105 for brand B and 1.67x105 for brand A. The organisms isolated from the three brands were identified as Bacillus cereus, Bacillus licheniformis, Bacillus coagulans, Bacillus stearothermophilus, Bacillus subtilis and Clostridium perfringens, with B. subtilis having the highest frequency of occurrence (93.33%). Samples were subjected to four different pasteurization treatments: 550C for 30 min, 800C for 15 min, 900C for 10 min and 1200C for 30 sec, to determine a more efficient process. No growth was observed on culture plates of samples pasteurized at 1200C for 30 sec, except on aerobic plates of brand A. However the milk samples treated under this regime curdled. Samples pasteurized at 800C for 15 min recorded the least counts next to samples treated at 1200C for 30 sec, without causing the samples to curdle.

Keywords: Evaporated milk, pasteurization, sporeforming bacteria, viable counts.

Nigerian Food Journal Vol. 25 (1) 2007: pp. 137-144