Fermentation
Fermentation
Microbiome, pre-, pro- and post-biotic – fermentation
The microbiome, pre-, pro- and post-biotics, as well as fermentation, are all concepts that are gaining increasing attention within both health and cosmetics. They are broad and complex topics, spanning from biology to product development, and are playing an increasingly important role in our understanding of the body – including its outer surface.
Here the focus is specifically on the skin and cosmetics. First, the microbiome is introduced with an emphasis on the skin microbiome, after which pre-, pro- and post-biotics are reviewed with a focus on their application in skincare products. Finally, attention is given to fermentation as a process that is increasingly used in the production of cosmetic ingredients.
PUCA PURE & CARE uses pre- and post-biotic ingredients, as well as ingredients produced through fermentation, in some of its products – for example, Yeast Ferment Extract and Lactococcus Ferment Lysate.
Microbiome
Microbiome” originates from Greek and means “small life” – a term used to describe the environment of microorganisms in a specific location. In some cases, it is used to describe the total genetic material of these microorganisms, but it is often used, like the term “microbiota,” to refer to the microorganisms themselves rather than just their genes. One can therefore speak of, for example, the gut microbiome and the skin microbiome.
There is no doubt that humans are entirely dependent on their microbiome to survive – we live together in symbiosis1. This is a very broad topic, and much is still unknown. Here, the focus will be on the skin microbiome and what may influence it.
The skin consists of several layers: the innermost layer is the subcutis (hypodermis), followed by the dermis, and the outermost layer is the epidermis. The epidermis constantly renews itself – this is referred to as skin (epidermal) turnover. The mechanism behind this continuous renewal is that the cells in the innermost layer of the epidermis, the stratum basale, continuously divide and form keratinocytes, which gradually migrate outward. On their way to the surface, these cells gradually change as they come to form the different layers of the epidermis, until finally – when they reach the outermost layer, the stratum corneum – they are shed and fall off. This turnover from stratum basale to stratum corneum takes approximately four weeks – it is slower in older skin and faster in, for example, psoriatic skin2.
The skin’s natural microbiota consists of many different microorganisms: bacteria, archaea3, fungi, viruses, and mites. They are found on the surface of the skin, in the upper layers of the epidermis, and, for example, in sweat glands and hair follicles. They are adapted to the specific environment of the skin that they colonize. There are resident microorganisms, which remain in the environment, and transient ones, which come and go. The skin can broadly be divided into three different types of microenvironments, which are decisive for which microorganisms colonize the area: sebum-rich areas (e.g. the T-zone of the face), moist areas (e.g. the armpit), and dry areas (e.g. the palms of the hands).
Depending on their symbiotic relationship with the host (in this case humans), microorganisms can be classified as commensals, which are present without causing harm; pathogens, which cause harm; and mutualists, which are beneficial. However, it is important to point out that in many cases it is the environment and the skin’s defense mechanisms that determine whether a microorganism behaves pathogenically or not. Thus, many of the microorganisms associated with skin diseases such as acne and atopic eczema are naturally present on the skin as commensals, and it is only in cases such as dysbiosis (imbalance) in the microbiome that they begin to act pathogenically. Therefore, microorganisms cannot be clearly divided into “good” and “bad.”
In relation to skin diseases and other skin conditions such as itching, infection, and dryness, it is not in all cases scientifically proven whether microbial dysbiosis is the cause of the skin condition or whether the skin condition is the cause of the dysbiosis. However, in many skin diseases and certain skin conditions, a clear association between the condition and dysbiosis is observed.
The microbiome and the skin cells constantly “communicate” and regulate the levels of various signaling molecules, etc., which is important for the development and stimulation of the skin’s immune system in close interaction with the microbiome. In this way, the skin learns to distinguish between different microorganisms and maintain a delicate balance between attacking “foreign” and tolerating “peaceful” microorganisms – a balance that is not always perfectly maintained.
Among other beneficial properties, it can be mentioned that some microorganisms produce vitamin K and B vitamins. The resident microorganisms inhibit the colonization of external microorganisms by their presence – they occupy space, “consume” nutrients (which may, for example, be waste products from the skin – meaning that the microbiome can in a way “clean” the skin), and secrete various substances such as antimicrobial peptides and fatty acids, which can make the environment unfavorable for other (e.g. pathogenic) microorganisms. Thus, the skin microbiome is also part of the outer “defense” that the skin provides for the body. The skin microbiome also contributes to maintaining the skin’s moisture level and skin barrier.
A very important point regarding the skin microbiome is that it is highly individual and that no standard has been established for what constitutes a “healthy” microbiome – each person has their own unique microbiome (even the microbiome on the right and left hand of the same person is different). Many factors determine an individual’s microbiome. In addition to the skin’s microenvironment, which is a very important factor, these include the level of inflammation in the skin, climate, as well as gender, age, hormonal status, genetics, use of medication, and of course hygiene and what is applied to the skin. It is therefore not straightforward to “balance” the microbiome using, for example, cosmetic products. However, there is gradually emerging evidence supporting some beneficial effects of certain biotics on the skin microbiome, although there is still a lack of clarity in the industry, for example regarding how the terms are used.
There is ongoing development within more personalized cosmetics, where efforts are being made to develop products that are better tailored to the individual, although this field is still not very advanced. Another growing initiative within the cosmetics industry is to investigate the impact of cosmetic products on the microbiome. Various types of tests have therefore been developed that can indicate whether a product affects the microbiome in a positive, neutral, or negative way and thereby support certain claims, such as microbiome-friendly cosmetics. Significant progress has also been made in microbiome analysis, which is applicable across many fields. However, much is still unknown about the microbiome, including details in its interaction with the skin and the body as a whole.
1 Symbiosis originates from Greek and means “living together.” The term is mainly used to describe a close association between two different organisms. A symbiosis can be beneficial for both parties and is then referred to as mutualistic symbiosis, or it can be beneficial for one organism and neutral for the other, in which case it is called commensal symbiosis, or it can be beneficial for one and harmful for the other, in which case it is called parasitic symbiosis.
2 More information about structure of the skin can be found in the description of Glycerin on this website
3 Archaea are one of the three domains of living organisms – the other two are bacteria and eukaryotes. In some respects, archaea resemble bacteria, for example in terms of size, and like bacteria they are unicellular organism.
Pre-, pro- and post-biotics
“Biotics” originates from the Greek “biōtikós” and means “related to life.” Pre-biotics can thus be translated as “before life,” while pro-biotics means “for life” and post-biotics “after life.” The first two terms are primarily known from the dietary supplement industry, while the latter is of more recent origin. Taken together, these concepts form the basis of one of the oldest processes we know within food production – namely fermentation.
Prebiotics: There is a reasonable consensus regarding the definition of prebiotics: they are substances that are selectively utilized by host microorganisms, conferring a health benefit to the host – which in this context is the human body.
They can thus be described as “food” for beneficial microorganisms, influencing the composition and/or activity of the microbiome in a way that benefits the body. One could say that there must be food before there can be life – hence prebiotics. Prebiotics are therefore, for example, substances that are not broken down and utilized by the body’s own enzymes but can instead be metabolized (fermented) by enzymes produced by beneficial microorganisms.
The largest group, and the “classical” prebiotics, are dietary fibers – complex carbohydrates in the form of various polysaccharides and oligosaccharides such as inulin and beta-glucans4. However, the group of prebiotics has gradually expanded, and other classes of compounds are now also considered to contain substances that can act as prebiotics, including conjugated5 linoleic acids, phenols, and certain other plant-derived compounds.
Probiotics have a fairly well-defined definition within the food industry, which is also gaining ground in the cosmetics industry. However, some have used the term more broadly than the definition allows. As a result, there are cosmetic products that carry the claim “probiotics” without meeting the definition established by FAO-WHO6 in a consensus statement: probiotics are defined as “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host.” In the early stages, when probiotics were new to the cosmetics industry, many manufacturers adopted a broader definition, so that, for example, substances derived from probiotic microorganisms and non-viable (dead) probiotic microorganisms (which would otherwise be classified as postbiotics) were also referred to as probiotics – notably without containing live microorganisms.
Live microorganisms are generally something manufacturers seek to avoid in their products, as microorganisms can be harmful and may spoil the product. In addition, SCCS (the Scientific Committee on Consumer Safety) has, in its guidelines for the testing and safety assessment of cosmetic ingredients, recommended limits for microbial content in cosmetics – guidelines that are generally followed.
Products that may support microbial growth – which applies to many cosmetic products – are therefore preserved, and microbiological testing is carried out to ensure that the products placed on the market are free from microorganisms and that the preservation system can eliminate microorganisms that may attempt to contaminate the product. One of the primary reasons for cosmetic products being recalled from the market is microbial contamination. Therefore, preservation and microbiological control are given high priority by most cosmetic manufacturers. As a result, including probiotics in the form of live microorganisms is not feasible in most current cosmetic products. This is due to several factors, including the fact that preservation systems will typically eliminate the microorganisms, as well as the challenges associated with controlling microbial growth while ensuring appropriate shelf life and product safety.
Some manufacturers attempt to overcome these challenges through various approaches. For example, by freeze-drying the microorganisms and subsequently incorporating them into a suitable formulation. However, it can be difficult to control how effectively the microorganisms become active again once applied to the skin and are expected to exert their beneficial effects. Microencapsulation and single-dose packaging, as known from dietary supplements, represent another, more technically demanding approach. The use of probiotics in anhydrous products (which do not require preservation) is another strategy employed by some manufacturers.
It is also worth considering whether probiotics containing live microorganisms are an effective way to influence the skin microbiome. A substantial number of microorganisms would likely be required, as the skin already harbors a large microbial population. In one study, researchers attempted an approach similar to fecal transplantation by transferring microorganisms from a healthy donor to another individual. Fecal transplantation has shown very promising results in several studies in the treatment of Clostridium difficile infection. In this small study involving skin microbiome transplantation on specific skin areas, it was observed that the recipient’s microbiome could shift toward that of the donor after three applications of 1 mL of a solution containing 10⁸ CFU/mL7, with changes detectable after several days.
There is also the concept of “synbiotics,” which is primarily used in relation to dietary supplements. This refers to a combination of prebiotics and probiotics – that is, microorganisms together with their “nutritional support,” intended to facilitate their establishment in a new environment. Probiotics used in cosmetics today most commonly belong to the genera Lactobacillus and Bifidobacterium.
Postbiotics are a relatively new concept within the “biotics family,” and there is not yet full consensus on the definition across all sectors. However, broadly speaking, they are inactive microorganisms and/or their components that confer a health benefit. Thus, they consist of components and substances derived from – typically probiotic – microorganisms. This makes it a very broad concept that encompasses highly complex mixtures.
What remains unclear is how much of the actual microorganisms must be present in order for a product to be classified as postbiotics. Some argue that, to be considered “postbiotics,” a product should contain parts of the microbial cells, the intracellular contents, and the substances produced by the cells (metabolites). Others also classify mixtures where cellular components have been removed, leaving “only” the metabolites, as postbiotics.
In relation to cosmetics, postbiotic mixtures are often identified through INCI names containing one or more of the following terms: the name of a microorganism, such as “Bacillus,” “Lactobacillus,” “Lactococcus,” or “Bifida,” as well as “Ferment,” “Ferment Filtrate,” or “Lysate.” In some cases, the INCI name also specifies the substrate used in the fermentation process, which may, for example, be plant-derived materials.
Postbiotics are typically produced via fermentation, where one or more specific probiotic microorganisms are provided with a substrate that they can break down and grow on, resulting in an increased number of microorganisms and the production of various metabolites. While some beneficial metabolites are known, these mixtures are generally chemically very complex, and much remains to be understood.
Postbiotics used in the cosmetics industry will generally not contain live cells and, in many cases, not even cellular components. Lysis is one method used to inactivate microorganisms, where the cell wall is broken down, for example through enzymatic processes or osmotic pressure, allowing the cellular contents to be released into the surrounding medium – resulting in lysates. Tyndallization is another method used to inactivate microorganisms through heat; this does not necessarily destroy the cell walls, but the cells are no longer viable.
4 More information about beta-glucans can be found in the description of Avena sativa on this website
5 Conjugated linoleic acids are a type of polyunsaturated lipid found, for example, in dairy products and meat.
6 FAO stands for the Food and Agriculture Organization, which is the United Nations’ organization for food and agriculture, while WHO stands for the World Health Organization. These two organizations collaborate in various areas.
7 CFU stands for Colony Forming Units. It is a measure of the number of viable microorganisms in a solution.
10⁸ CFU/mL means that in one milliliter of the solution, 100,000,000 microbial colonies will form when cultured.
Fermentation
Fermentation is a process that dates back thousands of years and remains highly important today. It is a natural biochemical process that occurs in countless variations, as many microorganisms – primarily fungi and bacteria – are capable of carrying out fermentation processes on different substrates and under varying conditions.
To mention just a few of the many areas in which humans utilize fermentation through microorganisms and their enzymes: the production of numerous natural raw materials for various industries, the breakdown of waste products, agricultural silage, enzyme production, and the preservation and production of many foods such as bread, yogurt, cheese, and alcohol.
Fermentation also takes place within the human body – particularly in the gut, where microorganisms contribute to the breakdown of food and produce metabolites, some of which are beneficial to the body. It can also be argued that the process occurring in working muscles during anaerobic activity, where lactic acid is formed, is a type of fermentation carried out by enzymes in muscle cells. Indeed, it is enzymes – most often from microorganisms – that drive fermentation processes.
There is no single, clearly defined and delimited definition of fermentation, other than that it is a metabolic process in which enzymes catalyze the chemical transformation or breakdown of organic material. The result is often a mixture of smaller molecules and inorganic substances. The most well-known fermentation process is likely the production of alcohol, in which enzymes from, for example, yeast of the genus Saccharomyces convert one glucose molecule into two ethanol molecules, while also producing carbon dioxide and generating energy for the yeast cell.
Fermentation can occur under anaerobic (without oxygen) and aerobic (with oxygen) conditions – although most fermentation processes are anaerobic. Fermentation is not always the same as decomposition, even though it can be described as a form of breakdown. Fermented foods are generally edible and are produced under carefully controlled conditions to ensure that undesirable “decomposition microorganisms” do not spoil the product. Decomposition processes occur naturally wherever there is heat, moisture, and microorganisms, whereas “beneficial” fermentation typically requires specific conditions. As an illustrative example, milk can become both sour milk (decomposition) and cheese (fermentation).
Some of the benefits of fermentation, for example in foods, include the formation of beneficial compounds such as antioxidants and flavor compounds, as well as increased bioavailability of many substances. Smaller molecules produced by microorganisms during fermentation are more easily absorbed, thereby potentially enhancing the nutritional value of the food. Fermentation can also be used to increase the value of large amounts of by-products generated by the food industry – fruit, vegetables, grains, dairy, and meat/fish by-products can serve as valuable resources that, through fermentation with different microorganisms, can be utilized more efficiently.
In addition to being used for the production of many specific substances applied in cosmetics, such as lactic acid, citric acid, and hyaluronic acid, there are numerous examples of fermented plant extracts with potentially interesting properties in relation to cosmetics – and there will undoubtedly be many more to come.
Summary
The microbiome plays a central role in maintaining the balance and function of the skin, and our understanding of this complex interaction is still evolving. Pre-, pro-, and post-biotics represent different approaches to influencing the microbiome; however, particularly within cosmetics, their application is still characterized by ongoing development and a lack of standardization.
At the same time, fermentation constitutes an important process in the production of ingredients and contributes complex mixtures of bioactive substances that may have relevant properties in skincare.
Overall, current developments indicate that the microbiome and biotics will play an increasingly important role in cosmetics, although further knowledge is still needed to fully understand and utilize their potential.
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