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 APPLICATIONS This 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.
Milk cream must be pasteurized in order to be sold in Brazil. However, there are no specific legal requirements for this product, and producers set their own pasteurization parameters using the ones approved for milk as a reference. Considering that fat protects bacteria from heat, that no thermal inactivation studies have been performed on Mycobacterium bovis present in cream, and that bovine tuberculosis is endemic in Brazil, the aim of this study was to evaluate the inactivation of M. bovis in milk cream subjected to commercial parameters of pasteurization. Milk cream samples were contaminated and pasteurized in a water bath at 75, 80, 85, and 90°C for 5 and 15 s. M. bovis cells were plated onto Stonebrink-Leslie medium, incubated at 36°C for 45 days, and quantified; the result was expressed in log CFU mL -1 . The fat content of the samples ranged from 34% to 37% and the average initial load of M. bovis was 8.0 Log CFU mL -1 . The average decay of the M. bovis populations was 4.0, 4.3, 4.9 and 6.7 log CFU mL -1 when the cream was treated for 15 sec at 75, 80, 85 and 90°C, respectively, showing that the efficiency of the heat treatment was improved by increasing the temperature of the process. Given the lipophilic nature of M. bovis, the cream should be subjected to more intense parameters of pasteurization than those applied to milk. Key words: Fat. Mycobacteria. Thermal death. Thermal treatment. ResumoA pasteurização do creme de leite é obrigatória no Brasil, mas não há parâmetros legais específicos para esse produto, de forma que as empresas estabelecem seus próprios parâmetros tendo como referência mínima os aprovados para a pasteurização do leite. Assim, considerando que a gordura tem efeito termo protetor para as bactérias, que não há estudos de inativação térmica do Mycobacterium bovis em creme de leite e que a tuberculose bovina é endêmica no Brasil, o objetivo deste estudo foi avaliar a inativação de M. bovis em creme de leite, submetido aos parâmetros comerciais de pasteurização. Amostras de creme de leite foram contaminadas e pasteurizadas em Banho-Maria a 75°C, 80°C, 85°C e 90°C, por
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