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From: Food Quality & Safety magazine, December/January 2007

Acidic Punch Pounds Pathogens

Octanoic Acid is Leading the Comeback of Fatty Acid-Based Antimicrobials

by Scott Burnett, PhD

Food processors and consumers are becoming more attracted to food preservation strategies with a focus on naturally occurring antimicrobials. Free fatty acids are widely distributed in nature and possess antimicrobial properties. This makes it a great time to consider new treatments which utilize these properties to deliver benefits valuable to processors.

Antimicrobial treatments are applied to foods as a measure to meet regulatory and consumer standards of safety as well as to enhance product shelf life. This provides extra assurance to food processors that they can preserve product quality and safety at a level higher than that which is achieved by standard sanitation operating procedures alone. When used properly, antimicrobial compounds applied to foods will exhibit the efficacy desired, have a negligible impact on product quality (with respect to organoleptic properties), and be cost-effective.

Fatty Acids as Antimicrobials

Much of the research work exploring the germicidal activity of fatty acids was done between 1920 and 1940. The discovery of penicillin in this era led researchers toward the pursuit of antibiotic isolation and the development of synthetic antimicrobials. The food industry is taking a second look at the benefits of fatty acids as antimicrobials, such as a lack of toxicity effects, excellent antimicrobial performance, and a broad distribution in nature.1 In recent years, fatty acids have been used commercially in such antimicrobial products as hard-surface sanitizers and disinfectants, teat dips, food additives, and processing aids.

From capric to linolenic, fatty acid biocidal activity has been investigated to some degree. The suitability of the different fatty acids for use as antimicrobials, that is, antimicrobial efficacy, impact to product sensory, ease of formulation, is dependent on the length of the carbon chain, the degree and structure of saturation, and the pH of the treatment solution and product. Fatty acids exhibit several mechanisms of antimicrobial action that are nonspecific, which may explain why no instances of fatty acid resistance development by microorganisms have been reported. Bacterial cell membranes are generally conceived to be the primary target of action whereby short- and medium-chained fatty acids in their protonated form dissociate upon diffusing into the protoplasm of the cell, leading the acidification of cellular components. At higher concentrations, fatty acids have been demonstrated to impede oxygen uptake and membrane-located transport of amino acids into the cell.2

Octanoic Acid Focus

Octanoic acid, also known as caprylic acid, is an eight carbon chain fatty acid that is generally recognized as safe (GRAS) (21 CFR 184.1025) by the FDA. The FDA’s evaluation of the safety of octanoic acid was based on its use as a flavoring agent and adjuvant in such food products as baked goods, cheeses, fats and oils, frozen dairy desserts, gelatins and puddings, meat products, soft candy, and snack foods. In nature, octanoic acid is present in human breast milk, bovine and goat’s milk, and coconut oil. Recently, octanoic acid was approved by the USDA/FSIS, for use as an antimicrobial for ready-to-eat (RTE) meat and poultry products. In commercial food processing, an octanoic acid-based antimicrobial treatment was recently introduced into the market by Ecolab and is available to processors throughout the United States. A broad spectrum antimicrobial, octanoic acid offers several significant benefits including:

  1. by nature, it is safe to handle and poses negligible safety risks to line workers;
  2. octanoic acid, when properly formulated, presents no impact to treated food product sensory;
  3. because octanoic acid is approved as a processing aid in the production of RTE meat and poultry products, there is no requirement for the treated product to be labeled as such.

A laboratory-based study was designed to evaluate the performance in killing Listeria monocytogenes on six RTE meat and poultry products. RTE products were inoculated with a five-strain mixture of L. monocytogenes and treated with an octanoic acid-based antimicrobial treatment. Following a procedure to recover the surviving pathogen from treated food product surfaces, reductions were determined based on non-treated controls. The experiments were conducted in triplicate. The octanoic acid-based antimicrobial treatment reduced L. monocytogenes numbers to between 1.03 log CFU per sample (oil-browned turkey surfaces) and 2.97 log CFU per sample (turkey sausage surfaces) when compared to untreated controls (Fig. 1).

Application Process

The commercial application of an octanoic acid-based antimicrobial treatment onto RTE meat and poultry products is both innovative and unique. The treatment solution is dispensed directly into the final shrink-film package as the RTE product is transferred into it. This reduces chemical usage and waste that are commonly associated with spray or immersion-style application systems. Moreover, the antimicrobial is applied directly into the final package, helping to virtually eliminate the possibility of a contamination event to occur after the application of the treatment. It’s the final step in assuring the protection of the product before it leaves the processing floor. Previous research has also shown that octanoic acid efficacy is enhanced by thermal activation. By increasing the time that packaged, treated RTE products are exposed to hot water under commercial shrink tunnels by just a few seconds, efficacy can increase significantly. This treatment solution is not for use to sanitize hard food contact surfaces such as tanks, lines, food processing equipment or to reduce microbial count in processing water, as to treat food packaging.

With these superior results, it’s clear that fatty acids are making their comeback and have found a fit in ensuring the quality and safety of foods as a new antimicrobial tool.

References:

  • Kabara, J. J. and D. L. Marshall. 2005. Medium-chain fatty acids and esters, p. 327-360. In P. M. Davidson, J. N. Sofos, and A. L. Branen (eds.), Antimicrobials in Food, 3rd ed. Taylor and Francis Group, LLC, Boca Raton, FL. Ibid.
  • Burnett S. L., J. H. Chopskie, T. C. Podtburg, T. A. Gutzmann, S. E. Gilbreth, and P. W. Bodnaruk. Use of octanoic acid as a post-lethality treatment to reduce Listeria monocytogenes on ready-to-eat meat and poultry products. Accepted for publication in Journal of Food Protection, early 2007.

Scott Burnett, Ph.D., is a scientist for Ecolab’s Food and Beverage Division in Eagan, Minn. The charge of his group is to develop innovative antimicrobial products for food surfaces and food processing environments. Scott can be reached at scott.burnett@ecolab.com.

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