Food Grade Preservatives

Posted by Remaining Third × 7:37 PM
This week's featured Ingredients are food-grade preservatives sometimes used in cosmetics and beauty products: benzoic acid, sorbic acid, levulinic acid, and their related salts.

Soya sauce contains sodium benzoate.


These preservatives are growing in popularity, particularly in the green/eco segment of the beauty market, mainly due to the negative press surrounding parabens, and to a lesser extent, phenoxyethanol (see earlier reviews of parabens here and phenoxyethanol here), and the belief that food-grade preservatives are safer to use. Let's take a closer look at them!

Benzoic acid has a long history, having been discovered back in the sixteenth century. It is the chief component of benzoin gum, a resin derived from several species of trees in the genus Styrax. It is also found in many other plants, particularly plants with berry fruit (e.g. cranberries, bilberries). Its antimicrobial effect was first noticed in 1875, and it has been used as a food preservative since then.

Harvesting resin from a Styrax benzoin tree;
the dried resin is sold as benzoin gum.

Benzoic acid
Salts of benzoic acid, e.g. sodium benzoate and potassium benzoate, are preferred as preservatives, as they are water soluble; they are commonly used in processed foods and drinks. In a water-based solution, the salt dissociates into the metal ion (sodium or potassium) and benzoate ion. Benzoic acid and benzoate are effective as preservatives at acidic pH levels.

There was some controversy in the 1990s when trace amounts of benzene were discovered in some soft drinks that had been stored for long periods of time. This is because under certain conditions, benzoic acid or benzoate ion can decarboxylate (i.e. lose its carboxylic acid group) to form carbon dioxide (CO2) and benzene, which is a known carcinogen. Two possible mechanisms for this decarboxylation reaction are shown below (Britt, P. F.,  et al. (1999, August). "Mechanistic investigations into the decarboxylation of aromatic carboxylic acids." In Conference: National American Chemical Society Meeting, New Orleans, Los Angeles.).
Proposed reaction mechanisms for decarboxylation of benzoic acid under acidic conditions,
such as commonly found in food and drinks. Benzene is the simple 6-member aromatic ring shown as the final compound in each reaction pathway (1) and (2).
(Source) 

In addition to the above mechanism, the decarboxylation of benzoic acid in water solution can also be catalyzed by the presence of ascorbic acid (Vitamin C) and a transition metal such as copper (II) and iron (III) (Gardner, L. K., et al. (1993) "Benzene production from decarboxylation of benzoic acid in the presence of ascorbic acid and a transition-metal catalyst." Journal of Agricultural and Food Chemistry 41(5): 693-695; source). Benzoic acid itself is believed to be relatively non-toxic. Benzene formation is believed to only be a concern if the preparation is stored for long periods of time and at appropriate reaction conditions that would allow it to form.

Like benzoic acid, sorbic acid was also first discovered as a component of a plant. In this case, sorbic acid was discovered in the berries of the rowan tree, Sorbus aucuparia, in 1859. The antimicrobial effect of sorbic acid was discovered in the late 1930s. Salts of sorbic acid are the preferred form, as they are water soluble. Potassium sorbate is a commonly used salt of sorbic acid.
Berries of the rowan tree;
sorbic acid is naturally occurring in these berries. 

Sorbic acid

Levulinic acid is yet another compound first derived from a plant, and later discovered to have an antimicrobial effect. Levulinic acid was first isolated from corn. As with benzoic acid and sorbic acid, you will see the salts of levulinic acid more commonly used in cosmetic formulations.
Corn (Zea mays).
Commercially available levulinic acid continues to be sourced from corn as it is so abundant.

Levulinic acid
Compared to parabens and phenoxyethanol, the food-grade preservatives including benzoic acid, sorbic acid and levulinic acid, are not as effective at inhibiting microbial growth. Typically you will see these preservatives in processed foods that have a limited shelf life or else they have special storage considerations, such as refrigeration or packaging with an air-tight seal. When used in cosmetics, the shelf life of the formulation is somewhat shorter compared to comparable formulations containing parabens or phenoxyethanol. Also, their antimicrobial activity is limited to formulations that are acidic (pH < 7), which limits the type of formulation they may be used in. In order to boost their efficacy, different food-grade preservatives are often combined to inhibit a broader range of microbes.

The Diane Lai body lotions contain sodium benzoate and potassium sorbate, but note that these lotions are also packaged in an air-excluding pump, which helps to protect the formulation.
Diane Lai Rejuvenate and Soothe lotions, along with the lip balms;
link to review here.
One of the original green/eco brands, Neal's Yard Remedies products incorporate levulinic acid or sodium levulinate, the sodium salt of levulinic acid.
Neal's Yard Remedies Baby Bath & Shampoo
contains levulinic acid.
(reviewed earlier here)
By now, I hope you will have seen a theme here: all of the preservatives I have reviewed thus far, including parabens and phenoxyethanol, are naturally occurring in various plants. All of these compounds serve the same purpose in plants as they do in cosmetic formulations: to protect from microbial growth, particularly fungal growth. For this reason, antimicrobial agents are often found in flowers and fruits, which are particularly prone to microbial attack, as they are loaded with sugars and nutrients. From an evolutionary standpoint, it makes sense for plants to protect these parts from microbes, as it is important for the plant to preserve the freshness of its flowers for pollinators and its fruits for passing birds and animals to consume (and then carry its seeds to other locations). It just so happens that parabens are very weakly estrogenic, while phenoxyethanol has negative side effects if consumed in high enough quantities: this again underlines the fact that just because something is natural does not mean it is automatically good for you! The food-grade preservatives appear to carry the least amount of risk but they are also not as effective as preservatives in cosmetic formulations. As stated before, it's up to the consumer to decide how much risk they are willing to take on when deciding on a beauty product.

***

On a personal note: apologies for my absence last week. Things got really crazy over the past two weeks and I am just catching my breath now. Doing my best to get back on track now! I am still working on my major review of a new brand, which I hope to complete soon.

In other news, Google Reader was retired on July 1. If you were using Google Reader and you don't have a Blogger account, you can continue to follow via Feedly as well as Bloglovin, Facebook and Twitter (for these last three, please click the appropriate media follow button over to the right). 
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1 comments

  1. AdamJuly 23, 2021 at 12:58 AM

    Consumers are sometimes unaware that phenoxyethanol suppliers for health care or skin care products use phenoxyethanol at a level where they can trust their product.

    ReplyDelete