Using nature’s molecular machines

In cosmetics, additives play an important role when it comes to making a product durable and creating a pleasant consistency. Fermentation is a good way to produce these naturally and therefore more sustainably. Dr Malte Sietzen and Dr Fernando Ibarra present some examples and their advantages.

Advantages of fermentation

Here, fermentation comes into play. Certain microorganisms can be enabled to convert non-expensive, ubiquitous vegetable feedstocks such as carbohydrates into valuable raw materials, which would otherwise be unobtainable, or burdened with considerable amounts of problematic byproducts. This approach offers several advantages over the methods of synthetic chemistry. It is relatively costand energy-efficient, the raw materials are often cheap and abundant, and chirality is easily introduced. Of course, the challenge is to find a suitable combination of microorganism and reaction conditions at which the desired chemical transformation is carried out economically on an industrial scale. But once such an opportunity has been identified, these microorganisms and their enzymes act as molecular machines, which, collectively, are powerful tools for scientists in search for more sustainable means of sourcing raw materials.

Xanthan gum

One example that is certainly known is xanthan gum, a polysaccharide comprising of a glucose polymer strand with complex sidechains, which is finding widespread use as a rheology modifier both in food as well as personal care applications. Xanthan is produced by fermentation of sugar- and nitrogen-containing feedstocks from the gram-negative bacterium Xanthomonas Campestris on an industrial scale.

The global yearly production is estimated to reach 100,000 t in the coming years. By manipulating process parameters during the fermentation procedure and through modifications performed after production, xanthan gums with varying characteristics can be obtained. Consequently, many different xanthan qualities with distinct properties exist on the market. For example, some qualities form completely transparent solutions while others do not. Some are vegan, some produce specifically highly viscous solution, colours can vary from white to shades of yellow, some are agglomerated to improve solubility, some are particularly tolerant to salts or varying pH, and so on.

Phenethyl Alcohol

Another example of a raw material obtained from fermentation is Phenethyl Alcohol – a fragrance compound revered not only for its odour, but also for its antimicrobial performance.

In contrast to the example of xanthan, the molecular structure is fairly unsophisticated, and accordingly the compound is readily available from petrochemical resources at low costs. But is there a way to obtain the molecule using carbon from renewable sources? Fortunately, there is: By utilising the yeast Saccharomyces Cerevisiae, natural phenylalanine obtained from plant sources can be converted efficiently into the desired phenethyl alcohol. As the vegetal origin of phenylalanine, we chose the roots (rhizome) of tobacco plants, which have been of little value to cultivators so far. Converting this scrap material into valuable natural phenethyl alcohol therefore perfectly represents a perfect waste to-value approach in sourcing raw materials. Phenethyl alcohol is suitable to achieve microbiological protection of all kinds of formulations, either acting alone, or as a boosting agent in conjunction with other antimicrobials.

Salicylic acid

For many years, salicylic acid has been used in personal care items for its keratinolytic properties and as a preservative. Just like in the example shown above, an inexpensive synthetic pathway is accessible from petrochemical sources. But why should we take this road when a more sustainable option exists? After all, salicylic acid is ubiquitous in many plants, most famously found in the bark of the willow tree. As it turned out, an efficient means of obtaining natural salicylic acid is starting from Gaultheria procumbens, also called checkerberry, or wintergreen. This plant contains large amounts of salicylate derivatives, mostly in the form of gaultherin.

Intriguingly, isolation of this compound is not necessary, because enzymatic hydrolysis of gaultherin is performed by the plants own enzyme gaultherase if the harvested plant material is subjected to the proper conditions. In this step, methyl salicylate is obtained, which is in turn converted into the desired salicylic acid.

Even though salicylic acid is listed as a preservative in the EU cosmetics regulation (EC) No 1223/2009, it is most often used as an active, treating for example callused feet, acne, or dandruff.

p-Anisic acid

Another example for which a convenient green synthetic approach exists as an alternative to conventional petrochemical means is p-Anisic acid. The starting point is the essential oil of star anise, from which several valuable substances, including anisic aldehyde, can be obtained. After distillative separation, anisic aldehyde is oxidised by action of the yeast Saccharomyces Cerevisiae, resulting in the generation of p-anisic acid. This fermentative approach yields the target molecule in high yield and purity and is thus an ideal alternative for sourcing the substance from sustainable resources. The antifungal action of p-anisic acid has been the focal point for its application in alternative preservation systems for several years now. Even at low concentrations of 0.1-0.3%, formulations are protected against microbiological spoilage if used in conjunction with another antibacterial such as levulinic acid. At the same time, p-anisic acid is safe to use and exhibits no irritation potential. Increasing the efficacy with preservative boosting agents like Pentylene Glycol broadens the range of applications even more.

The list of powerful raw materials obtained from fermentation is long and cannot be covered here in full. To name a few more examples, Zemea propanediol by DuPont/ Tate&Lyle is 1,3-propanediol obtained from corn sugar through bacterial fermentation. Jungbunzlauer is manufacturing L(+)-lactic acid and gluconic acid, as well as their salts and derivatives, by fermentation from carbohydrates. And even hyaluronic acid, a compound ubiquitous in anti-ageing applications, is today mostly generated by those molecular machines. Considering the variety of microorganisms living alongside us on this planet, the potential for further application of fermentation technology and enzymatic catalysis is evident. It is our hope that in the future, many more companies will embrace this climate-friendly means of production, which will be an important puzzle piece in helping us to avert the looming climate crisis. After all, admiring nature’s wonders is an excellent pastime – but applying their principles by creating valuable and sustainable raw materials might be a gamechanger.