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Woody’s Consumer Brands consider the use of Lamirsa’s Ethyl Lauroyl Arginate as a food preservative in one of its products. Here we try and understand its background and the mechanism behind its functionality as a food preservative.
In the 1980s a Spanish company, based in Barcelona, LAMIRSA, began research on the use of cationic surfactants to prevent the proliferation of a wide variety of bacteria moulds and yeast in foods.
A surfactant is a surface-active agent. The molecule comprises a head and one or two tails. Surfactants are classified according to the characteristics of the polar head group being nonionic, anionic, cationic or amphoteric.
A non-ionic surfactant has no charged groups in its head. If the charge is negative, the surfactant is called anionic; if the charge is positive, it is called cationic. Amphoteric surfactants have the ability to change from cationic to anionic surfactants. (elementis-specialties.com)
The main application of cationic surfactants relates to their adsorption at surfaces. Examples of such surfaces are steel, mineral ores, inorganic pigments, plastics, fibers, hair, fertilizers and, our main area of focus, bacteria cell walls.
The biggest number of cationic surfactants are nitrite based compounds and “the main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs).” (Carmona-Ribeiro, A. M. and Dias de Melo Carrasco, L.)
Ammonium is represented by . Quaternary ammonium cations or quats are positively charged polyatomic ions of the structure . R is either an alkyl group or an aryl group. A unique and useful feature of the quaternary ammonium cation is that they are permanently charged, independent of change in pH of the solution. This is in contrast to the ammonium ion (), and the primary (three hydrogen atoms and one R group attached to a nitrite atom), secondary (two hydrogen atoms and two R groups attached to a nitrite atom) and tertiary ammonium cations (one hydrogen atoms and three R group attached to a nitrite atom). (CTI Reviews)
QAC’s interact with microorganisms predominantly in relation to the cell wall in a destructive way which makes them ideal anti-microbial agents.
“QACs are membrane-active agents (i.e., with a target site predominantly at the cytoplasmic (inner) membrane in bacteria or the plasma membrane in yeasts). The following sequence of events occurs with microorganisms exposed to cationic agents:
(i) adsorption and penetration of the agent into the cell wall;
(ii) reaction with the cytoplasmic membrane (lipid or protein) followed by membrane disorganization;
(iii) leakage of intracellular low-molecular-weight material;
(iv) degradation of proteins and nucleic acids; and
(v) wall lysis (the cell wall or membrane ruptures and the cell disintegrates) caused by autolytic enzymes (its own enzymes or enzyme from another of the same molecule).
There would be a loss of structural organization and integrity of the cytoplasmic membrane in bacteria, together with other damaging effects to the bacterial cell.
Actually, most studies on membrane damage evaluated the effects of biocides on protoplasts and spheroplasts suspended in various solutes. QACs caused lysis of spheroplasts and protoplasts suspended in sucrose. The cationic agents interact with phospholipid (the phosphate group being the negatively-charged polar head) components in the cytoplasmic membrane, thereby producing membrane distortion and protoplast lysis under osmotic stress. Isolated membranes, however, did not undergo disaggregation (separation out) on exposure to QACs. Some polymeric quaternary ammonium compounds such as polyquaternium-1, a quaternary ammonium polymeric compound, and myristamidopropyl dimethylamine, were shown to induce lysis of spheroplasts of S. marcescens, but not those of C. albicans. Damage to the membrane was sufficient to cause K+ leakage but this injury was not always sufficient to cause spheroplasts lysis. Adsorption of dioctadecyldimethyl ammonium bromide (DODAB) cationic bilayers onto bacterial cells changed the sign of the cell surface potential from negative to positive and a clear relationship between positive charge on bacterial cells and death was described. Regarding the mechanism of DODAB action, neither bacterial cell lysis nor DODAB vesicle disruption took place in contrast to the mechanism of action for single chained cationic surfactants.” (Carmona-Ribeiro, A. M. and Dias de Melo Carrasco, L.)
ETHYL LAUROYL ARGINATE
Ethyl Lauroyl Arginate is synthesised by esterifying arginine with ethanol, followed by reacting the ester with lauroyl chloride. The resultant ethyl lauroyl arginate is recovered as hydrochloride salt and is a white, solid product that is filtered off and dried.
Carmona-Ribeiro, A. M. and Dias de Melo Carrasco, L.. 2013 May. Cationic Antimicrobial Polymers and Their Assemblies. Int J Mol Sci. 2013 May; 14(5): 9906–9946. Published online 2013 May 10. doi: 10.3390/ijms14059906
CTI Reviews. 2017. Organic and Biological Chemistry, 6th Edition. Content Technologies, Inc.