PERFORMANCE OF PETRIFILM AEROBIC COUNT PLATES ON ENUMERATION OF LACTIC ACID BACTERIA IN FERMENTED MILKS

Abstract

ABSTRACT This study aimed to compare Petrifilm Aerobic Count (AC) plates and the conventional pour plate methodology using the de Man–Rogosa–Sharpe (MRS) agar for the enumeration of lactic acid bacteria (LAB) in fermented milks (FMs), with different starter cultures added. FM samples (n = 66) were collected and plated on both methodologies, with incubation under anaerobic conditions at 35C for 48 h. The count results were compared by analysis of variance (P ≤ 0.05) and regression analysis. No differences between the mean counts obtained by both methodologies were observed, even when distinct FMs were compared. Considering all samples, a high correlation level was obtained between Petrifilm AC and MRS agar (r = 0.92), but these indexes were lower in FMs with Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (r = 0.90) and Lactobacillus fortis (r = 0.81). Despite some slight interferences, Petrifilm AC has proven to be a convenient methodology on enumerating LAB in FM.PRACTICAL APPLICATIONSThis study focused on the evaluation of an important tool for monitoring the microbiologic quality in the food industry. Petrifilm plates are widely used in the food industry, and their application for several microorganisms groups and foods must be properly evaluated for convenient application. Petrifilm Aerobic Count (AC) plates, associated to the de Man–Rogosa–Sharpe broth, were already described as adequate for the lactic acid bacteria (LAB) enumeration in foods. However, A previous study was conducted only with experimental inoculation of LAB in sterile milk and naturally occurring LAB in raw milk (Nero et al. 2006). This article is a complement of the first one, and we show the convenience of Petrifilm AC plates on LAB enumeration in fermented milks, considering different types of LAB starter cultures on the performance of this methodology.