This study aimed to evaluate the behavior of Petrifilm™ Lactic Acid Bacteria Count Plates (PLAB) as an alternative methodology to enumerate lactic acid bacteria (LAB) in bacon. Bacon samples (n = 40) were obtained from retail sale, ten-fold diluted with buffered peptone water (BPW, 0.2% w/v) and Letheen broth, and subjected to LAB enumeration according to 4 protocols: 1) de Man Rogosa Sharpe agar (MRS), pH 5.7, 30 °C; 2) MRS, pH 5.7, 30 °C, anaerobiosis; 3) all purpose tween agar (APT), 25 °C; 4) PLAB, 30 °C. Colonies were enumerated at 24, 48 and 72h, and the results expressed as log 10 CFU/g for comparison by ANOVA and regression (p < 0.05). Further, colonies were randomly selected and characterized as LAB (Gram staining and catalase). Mean LAB counts from MRS and PLAB did not present significant differences independently of incubation time or diluent (p > 0.05), while counts in APT with BPW after 24h were significantly lower (p < 0.05). PLAB counts with BPW (24, 48, 72 h) presented significant correlation with MRS (r ranging from 0.87 to 0.89; in anaerobiosis, r ranging from 0.94 to 0.95) and APT (r ranging from 0.84 to 0.86). With Letheen, PLAB (24, 48, 72h) presented significant correlation with MRS (r ranging from 0.92 to 0.94; in anaerobiosis, r ranging from 0.93 to 0.96) and APT (r ranging from 0.77 to 0.79). A total of 1,032 from 1,063 (97%) colonies was characterized as LAB. Based on the obtained results, PLAB can be considered as an alternative tool for enumerating LAB in bacon, with reliable results even after 24 h of incubation.
Microbial enumeration by serial dilution is one of the best resources to estimate cellular density for microbiological analysis. However, for metataxonomic analysis it is not clear if serially diluted samples may accurately be used for metataxonomic analysis to represent species composition in beef samples. In this study, the effect of sampling preparation of beef samples on the bacterial composition was evaluated by the comparison of dilution and exudate. Based on the obtained results, data obtained from the exudate of the samples were more robust in terms of number of generated reads, but no significant differences in terms of biological diversity were observed (p < 0.05, Wicoxon Test). Besides, both sample preparation procedures evidenced equivalent results of bacterial composition as well as its relative abundances. In conclusion, the use of exudate allows bacterial enumeration and metataxonomic analysis, which is interesting for the point of view of food microbiologists as cellular loads and microbial composition of culturable and unculturable bacteria could be compared.
A carne bovina é uma das variedades de carne mais consumidas no mundo e tem relevante importância para e economia. A embalagem a vácuo é comumente utilizada para estender a vida útil deste produto, impedindo a multiplicação de microrganismos aeróbios. No entanto, o ambiente de anaerobiose gerado permite a multiplicação de microrganismos anaeróbios, como Clostridium spp., que podem causar prejuízos consideráveis às indústrias de alimentos, como a deterioração blown pack. O objetivo do estudo foi associar a presença e contagens de Clostridium sulfito redutor e Clostridium perfringens em carne bovina embalada a vácuo com a deterioração blown pack, considerando diferentes temperaturas de conservação. Amostras de carne bovina embalada a vácuo (n = 10) foram armazenadas a 4 °C e 15 °C durante o período de 28 dias, com monitoramento semanal das contagens de Clostridium sulfito redutor e C. perfringens e verificação da presença da deterioração blown pack. A presença de clostrídios sulfito redutores e C. perfringens foi constatada em 70% das amostras. Dos isolados característicos obtidos, 100% foram confirmados como Clostridium sulfito redutores e 79,8% foram identificados como C. perfringens. A contagem máxima de Clostridium sulfito redutor a 4 °C e 15 °C foi de 0,39 log10 UFC/g e 2,03 log10 UFC/g, respectivamente. A contagem máxima de C. perfringens a 4 °C e 15 °C foi de 0,18 log10 UFC/g e 1,74 log10 UFC/g, respectivamente. Alternativamente, observamos o surgimento da deterioração blown pack em 90% das amostras armazenadas a 15 °C. Através dos resultados obtidos, podemos concluir que a temperatura de refrigeração a 4 °C controlou a multiplicação desses microrganismos quando comparado com a temperatura inadequada de armazenamento, a 15 °C, durante o período de 28 dias. Além disso, concluímos que a carne bovina embalada a vácuo, quando armazenada em temperatura inadequada de 15 °C, em um período aproximado de 7 a 21 dias, pode apresentar o surgimento da deterioração blown pack. Palavras-chave: Carne bovina. Clostridium spp. Clostridium perfringens. Blown pack.
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