Título da Dissertação:  Inibição de Salmonella Typhimurium pela combinação de carvacrol e sorbato de potássio in vitro e em polpa de tomate.

Orientadora: Profa. Dra. Jane Martha Graton Mikcha

Data da Defesa: 26/02/2018



INTRODUCTION: Foodborne diseases outbreaks caused by Salmonella spp. involving fruits, vegetables and some processed foods have been reported. Chemical preservatives, such as potassium sorbate (P.S.), are employed on a large scale by the food industry for microbiological control of these foods. However, its excessive consumption has negative effects on human health. In recent years, essential oils and their specific components have shown to be an option for use in food due to their antibacterial activity and because they are considered “Generally Recognized As Safe (GRAS) substance” by Food and Drug Administration (FDA). Carvacrol is a component of origanum and thymus essential oils and has been shown to be active against a broad spectrum of microorganisms, but its use in high concentrations may cause negative modifications in the food´s sensorial characteristics. The combined use of antimicrobial compounds is an alternative to reduce the concentration of synthetic additive and natural antimicrobial at sub-inhibitory concentrations with same antibacterial effect.

AIM: The objective was investigate the antibacterial effects of carvacrol and P.S. alone and in combination against Salmonella Typhimurium in vitro and in tomato paste. Physicochemical and sensory analysis of these products were also performed.

MATERIAL AND METHODS: The bacterial strain used was Salmonella enterica serotype Typhimurium ATCC 14028. The antimicrobial activity in vitro of carvacrol and P.S. alone and combined was determined by minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), checkerboard and time-kill assay. Antibacterial activity of these compounds on tomato paste was evaluated with carvacrol at 78 μg/mL (TCar), P.S. at 39 μg/mL (T.S.P.) and the mixture at same concentrations (TCar+P.S.). It was also evaluated a control that consisted on tomato paste without carvacrol and P.S.; Control and treatment groups were stored at room temperature for 10 days. S. Typhimurium experimentally inoculated on tomato paste was enumerated on days 0, 1, 2, 3, 4, 5, 8 and 10 of shelf life. Coagulase-positive staphylococci, Salmonella spp., coliforms at 35 °C and 45 °C, mold and yeast, and mesophyll bacteria were evaluated on days 0, 5 and 10 of shelf life, and also pH, soluble solids and reducing sugars analysis on tomato paste were realized on the same days. Analyses were performed in duplicate, with two replications. The sensorial analysis was performed by 120 untrained panelists, which evaluated the acceptability following attributes color, texture, taste, appearance and overall acceptability by applying the 9-point hedonic scale.

RESULTS: MIC of carvacrol and P.S. for S. Typhimurium were 312 μg/mL and 1250 μg/mL, respectively and the MBC was 312 μg/mL for carvacrol and 1250 μg/mL for P.S. Carvacrol and P.S. presented additive interaction against S. Typhimurium by Checkerboard assay. In time-kill curve, carvacrol at 78 µg/mL failed to reduce the bacterial population at any of the times under evaluation, while P.S. at 39 μg/mL completely inhibited bacterial growth after 96 h. No viable cells were observed after 48 h in the treatment with carvacrol (78 μg/mL) + P.S. (39 μg/mL).

In tomato paste, S. Typhimurium counts reached approximately 6.3 log CFU/g on the tenth day, in control group. Bacterial counts in tomato paste treated with carvacrol (TCar) were reduced by approximately 4 log CFU/g on the tenth day when compared to control group. The treatment with P.S. (TP.S.) completely inhibited bacterial growth on the eighth day. The application of carvacrol + P.S. (TCar+P.S.) significantly reduced bacterial counts by approximately 1.5 log CFU/g on first day and approximately 3 log CFU/g on second day when compared to control group (p < 0.05). No viable cells were observed on third day of storage. The microbiological analyses of tomato paste demonstrated that in control and treatment groups (TCar, TP.S. and TCarv+P.S.) the counts of coliforms at 35 °C and 45 °C were <3 MPN/g during shelf life. Mesophilic bacteria population was < 1 log CFU/g and coagulase-positive staphylococci, molds and yeasts counts were < 2 log CFU/g for all samples during the entire storage period. Salmonella spp. was absent in all treatment and control groups on different days evaluated. Regarding the physicochemical parameters it was observed that pH values ranged between 4.8 and 5.0 in control and treatment groups on all days evaluated. Soluble solid rates ranged between 7.5 and 8.8 % on all days of shelf life. Results obtained reducing sugar content analysis ranged between 3.7 and 4.7 % in control and between 3.0 and 5.8 % on TCar, TP.S. and TCar+P.S. during the storage period. In general, sensorial analysis showed good acceptance of tomato paste with carvacrol (TCar), P.S. (TP.S.) and the mixture (TCar+P.S.). Significant differences were found only for taste and overall acceptance in tomato paste sample with carvacrol (TCar) and carvacrol + P.S. (TCar+P.S.). To attributes color, texture and appearance no significant difference was found between treatment and control groups.

CONCLUSIONS: Results of current study showed the efficacy of carvacrol and P.S. in inhibiting the in vitro growth of S. Typhimurium and in tomato paste. The combination between carvacrol and P.S. did not change the physicochemical properties of tomato paste that presented good acceptance by panelists. Our results reinforced the idea that the mixture of natural compounds with synthetic preservative might be an alternative to improve the microbiological quality and safety without affect the sensory perception of tomato paste.

Key words: combined application; antibacterial activity; microbiological quality; natural antimicrobials; synthetic preservatives; processed foods.


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