Antibacterial activity of selected fatty acids and essential oils against six meat spoilage organisms
Introduction
The problem of safe preservation in the meat industry has grown to be more complex as today's products require longer shelf-life and greater assurance of protection from microbial spoilage. Many attempts have been made to control microbial growth at the surface of meat and meat products with antimicrobial chemicals. For example, significant reductions of microbial growth were obtained by dipping or spraying meat with organic acid solutions (Abugroun et al., 1993, Anderson and Marshall, 1989). However, preservatives could not be stabilized at the surface of food due to evaporation, neutralization (Siragusa and Dickson, 1992), and diffusion into the matrix (Torres et al., 1985).
Fatty acids and essential oils have also been shown to possess antibacterial and antifungal activities against many plant and food microorganisms (Kabara, 1981, Shelef et al., 1980, Russel, 1991). Gram-negative bacteria were shown to be generally more resistant than gram-positive ones to the antagonistic effects of fatty acids and essential oils because of their cell wall lipopolysaccharide (Kabara, 1979, Branen et al., 1980, Russel, 1991) but this was not always true (Karapinar and Aktug, 1987). In addition, most studies to date have been done with pathogens such as Salmonella typhimurium and Staphylococcus aureus (Karapinar and Aktug, 1987, Paster et al., 1990, Juven et al., 1994), Listeria monocytogenes (Aureli et al., 1992, Wang and Johnson, 1992), Vibrio parahaemoliticus (Karapinar and Aktug, 1987, Shelef et al., 1980), and Clostridium botulinum (Ababouch et al., 1992), and little is known about the effect of these compounds on meat spoilage bacteria such as Carnobacterium piscicola, Lactobacillus curvatus and Lactobacillus sake.
An investigation is currently under way in our laboratory to develop active packaging materials for the preservation of meat products. As a first step, it was necessary to know how the regular meat flora was affected by antibacterial agents currently approved for food use, in particular fatty acids and essential oils. The purpose of the present study was therefore to evaluate the efficacy of various fatty acids and essential oils to control the growth of meat spoilage organisms.
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Organisms and cultures
The following organisms were obtained from the American Type Culture Collection (Rockville, MD, USA); Carnobacterium piscicola (ATCC 43224), Lactobacillus curvatus (ATCC 25601), and Lactobacillus sake (ATCC 15521). Pseudomonas fluorescens and Brochothrix thermosphacta were isolated from beef stored at 4°C (Farber and Idziak, 1984). Serratia liquefaciens was isolated from vacuum packaged bologna (Food Research and Development Centre, St. Hyacinthe, Québec).
P. fluorescens, B. thermosphacta, and
Fatty acids
All the fatty acids failed to inhibit B. thermosphacta, P. fluorescens, and S. liquefaciens at concentrations up to 2500 μg/ml (results not shown). The inhibitory effects against the three other bacteria (C. piscicola, L. curvatus, and L. sake) are presented in Table 1. All were unaffected by myristic, palmitic, stearic, and oleic acids at the concentrations tested. Lauric, palmitoleic, linoleic, and linolenic acids exhibited various inhibitory activity with lauric and palmitoleic acids having
Discussion
The two gram-negative bacteria (P. fluorescens, and S. liquefaciens) were unaffected by fatty acids at concentrations up to 2500 μg/ml. This was to be expected since several other studies (Kabara, 1979, Kabara, 1981, McKellar et al., 1992) reported that gram-negative bacteria were resistant to the inhibitory effects of medium and long chain fatty acids and their derivatives. This resistance has been attributed to the presence of cell wall lipopolysaccharides, which can screen out the fatty
Acknowledgements
This research was made possible by the financial support of Programme Canadien des Bourses de la Francophonie, Agence Canadienne du Développement International, Ottawa, Ontario. The expert technical assistance of Yves Raymond is greatly appreciated
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