Antibacterial Activity-Guided Fractionation of Kimchi Fermentate Finds Salicylic Acid and Didecyldimethylammonium Bromide as Actives

 

Reviewed: Li J, Chaytor JL, Findlay B, McMullen ML, Smith DC, Vederas JC. Identification of didecyldimethylammonium salts and salicylic acid as antimicrobial compounds in commercial fermented radish Kimchi. J Agric Food Chem. 2015;63(11):3053–3058.

 

Keywords: Raphanus raphanistrum subsp. sativus, kimchi root, fermentate, adulteration, synthetic antimicrobial compound, didecyldimethylammonium bromide, salicylic acid

 

The roots of radish (Raphanus raphanistrum subsp. sativus, syn. R. sativus, Brassicaceae) are widely used in food, especially as salad vegetables. Radish is also a frequent ingredient of kimchi, a traditional Korean side dish made from fermented vegetables. A product made from radish fermented with Leuconostoc kimchi, a Gram-positive bacterium, is currently sold as natural preservative ingredient, in particular to the cosmetic industry. The product, sold under the brand name Leucidal^® (manufactured by Active Micro Technologies, Lincolnton, NC), inhibits growth of a number of bacteria at concentrations above 0.8-2.4%. The purported active compound is an antimicrobial peptide of unknown chemical structure.¹

 

Researchers from the University of Alberta (Edmonton, AB, Canada), Saginaw Valley State University (University Center, MI) and Griffith Laboratories, Ltd. (Toronto, ON, Canada) started an investigation into the identity of the antimicrobial peptide in question. Antibacterial activity-guided fractionation led to the isolation of two compounds, salicylic acid and didecyldimethylammonium bromide, both of which exhibited modest antibacterial activities.

 

Salicylic acid is a natural product that can be produced from fermentation of radish. In order to determine if the salicylic acid and didecyldimethylammonium bromide in Leucidal originated from the fermentation process, or was added as a low-cost antimicrobial compound made by chemical synthesis, the researchers submitted the two isolates to analysis of radioactive carbon 14 (¹⁴C) dating. The ¹⁴C isotope, which has a half-life of 5730 years, is incorporated into living plants in minute amounts as part of the photosynthesis – once the plant dies, no additional ¹⁴C is incorporated; the amount of ¹⁴C present can therefore be used to determine the age of a plant. Fossil fuel-based materials have little or no ¹⁴C contents. According to this data, salicylic acid and didecyldimethylammonium bromide were found to be 52,000 ± 2900 and 21,140 ± 100 years old, respectively. In other words, these compounds were made by chemical synthesis using fuel-based starting materials, and were added to the radish fermentate to make up for an otherwise inactive ingredient.

 

Comment: The search for safe and effective natural ingredients to preserve liquid and semi-solid (e.g., creams and ointments) formulations is a high priority among suppliers to and researchers of the cosmetic and personal care industry. Various ingredients of natural origin are offered on the market, but more often than not these products are either ineffective, have an unappealing color or odor, or are too expensive to be used in a formula. Unfortunately, low-cost products with efficacy against a large number of bacteria, yeasts, and fungi may turn out to contain undeclared synthetic antimicrobial actives, as in the case of the so-called “grapefruit seed extract”.² As evidenced in the case of this radish fermentation product, the recipe can be easily transposed to other ingredients. Of particular concern is the addition of didecyldimethylammonium bromide, which is a quaternary ammonium salt devoid of a chromophore; therefore, it will go undetected if a product is analyzed by methods using UV/Vis detection (e.g., high-performance liquid chromatography [HPLC]-UV/Vis).

 

References

1.     Leucidal^® Liquid technical data sheet. Lincolnton, NC: Active Micro Technologies, LLC. 2014. Available at: http://activemicrotechnologies.com/wp-content/uploads/2014/04/M15008-Leucidal-Liquid-Technical-Data-Sheet-v14.pdf. Accessed February 13, 2017.

Cardellina JH. Adulteration of commercial “grapefruit seed extract” with synthetic antimicrobial and disinfectant compounds. HerbalGram. 2012;94:62-66.