Abstract
Although carvacrol (CAR) is considered an alternative antimicrobial for use in food, few is known about the influence of food-related parameters on its inhibitory effects against pathogens. This study assessed the influence of different amounts of proteins, using beef extract (BE) as a protein-rich source, lipids (LIP), using sunflower oil as a LIP-rich source, and pH values or their interaction on the inhibitory effects of CAR against Salmonella Typhimurium PT4 (ST) and Escherichia coli O157:H7 (EC). The specific maximum growth rate (μmax) and lag phase duration (λ) of the test pathogens when exposed to CAR in media with different amounts of BE (4, 6, and 8 g/100 mL), LIP (3.75, 5, and 6.25 mL/100 mL), and pH values (5, 5.5, and 6) were determined. The viable counts of the tested pathogens in media that promoted the highest and lowest μmax in the presence of CAR were monitored during 24 h. The lowest μmax of ST and EC exposed to 2.4 μL/mL (-1.29 and -0.82 log CFU/mL/h, respectively) or 4.8 μL/mL CAR (-1.44 and -2.17 log CFU/mL/h, respectively) were observed in media with the highest LIP amount (6.25 mL/100 mL) and pH value (pH 6). For both SE and EC, the longest λ (> 2 h) was verified in media where these pathogens showed the lowest μmax. These data indicate that the concomitant increase in LIP amounts and pH values affected positively the CAR inhibitory effects against the target pathogens. CAR (2.4 or 4.8 μL/mL) failed to inhibit the increase in ST and EC counts in media where the highest μmax values were previously observed. On the contrary, CAR inhibited the increase of ST counts (final counts 5 log CFU/mL) and decreased the EC counts (final counts 3.5 log CFU/mL) in media where the lowest μmax values were observed. These results show that the inhibitory effects of CAR on ST and EC in food matrices could be affected as a function of the interaction of LIP amounts and pH values.
Highlights
Antimicrobial preservatives have been largely used to ensure food safety and reduce the risk to consumers (Tiwari et al, 2009; Lucera et al, 2012)
Typhimurium PT4 (−1.44 log CFU/mL/h) exposed to 4.8 μL/mL CAR was observed in medium with the highest amount of beef extract (BE) (8 g/100 mL) and LIP (6.25 mL/100 mL) at pH 6.0
Typhimurium PT4 (−1.29 CFU/mL/h) showed the lowest μmax when exposed to 2.4 μL/mL CAR in medium with 4 g/100 mL BE and 6.25 mL/100 mL LIP at pH 6.0
Summary
Antimicrobial preservatives have been largely used to ensure food safety and reduce the risk to consumers (Tiwari et al, 2009; Lucera et al, 2012). Increasing consumer awareness and concern regarding the use of synthetic preservatives in foods has increased demand for foods with low amounts or free of synthetic preservatives (Lucera et al, 2012; Souza et al, 2016). In this context, efforts have been conducted to study natural substances capable of preventing bacterial growth and survival in foods (Hintz et al, 2015; de Souza et al, 2016). The in vitro antibacterial properties of CAR have been demonstrated in different food matrices, such as vegetables (Oliveira et al, 2015), fruit juices (Ait-Ouazzou et al, 2013), peanut paste (Chen et al, 2015), cheese (Honório et al, 2015), and meat (Luz et al, 2014)
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