500 JOURNAL OF COSMETIC SCIENCE
issues with resistance to antibiotics and antimicrobials may make botanicals an attractive
choice, and the sustainability of chemicals extracted from plants.59,60
Evans and Cowan59 reported that phytochemicals can be divided into several categories
based on their structure: simple phenols (e.g., catechol and pyrogallol), phenolic acids (e.g.,
cinnamic and caffeic acids), quinones (e.g., hydroquinone), flavonoids (e.g., glycyrrhizin from
licorice), tannins which are found in green tea and red wine, coumarins, terpenoids (e.g.,
menthol), alkaloids (e.g., berberine), and lectins/polypeptides which form ion channels in
the microbial membrane or act as competitive inhibitors of microbial adhesion proteins to
host polysaccharide receptors. Rosemary, Rosmarinus officinalis, is an aromatic plant from the
Lamiaceae family. Rosemary extracts contain phenolic acids, flavonoids, and diterpenoids,
and have been used for preventing oxidation and microbial contamination. Cinnamic acid
and caffeic acids are bioactive phytochemicals that have a single substituted phenolic ring.
Tarragon and thyme contain caffeic acid which has antibacterial and antifungal properties.
Thyme oils with the highest concentration of phenols (e.g., thymol and carvacrol) were
reported to have the highest antimicrobial activity. Coumarins are phenolic substances
containing fused benzene and α-pyrone rings. Over 1,000 coumarins have been identified,
and many are reported to have antimicrobial activity.59,60
Hamilton-Miller indicated that antimicrobial compounds including polyphenolic
compounds in tea (e.g., catechins, theoflavins and theorubigins) inhibited several
microorganisms including S. aureus, Salmonella typhi, Pseudomonas spp., and Trichophyton
mentagrophytes.61 In another report, Hamilton-Miller observed that simple catechins in
green and black tea made from dried leaves of Camellia sinensis inhibited Streptococcus mutans
and S. sobrinus in vitro.62 They suggested that the in vitro effects may translate into caries
prevention as a result of drinking regular tea. They noted that there was some disagreement
over precisely which bacterial species were inhibited by tea due to strain differences and
how the tea infusions were prepared.61
Extracts from botanicals including rosemary, sage, tea, thyme, eucalyptus, willow bark,
and woodruff are multifunctional ingredients that have antimicrobial and antioxidant
properties. Botanical extracts may not provide adequate preservation when used as
the sole preservative in a formula, but they may contribute to the preservative systems
of cosmetic and drug products. It is necessary to test potential botanical candidates
in prototype formulations to assess their antimicrobial activity and select sustainable
botanical ingredients to be part of a preservative system. Readers wanting to learn more
about preservation with phytochemicals are directed to the works of Evans and Cowan59
and Nieto.60
HURDLE TECHNOLOGY: USE OF ENZYMES AND MICROBIAL FERMENTS
Enzymes are biological catalysts that carry out essential functions in living organisms.
Enzymes that function as part of an organism’s defense system typically are lytic or
oxidoreductase enzymes. Lytic enzymes such as lysozyme (i.e., N-acetylmuramidase) attack
the β-1,4-glucosidic linkages of the peptidoglycan cell wall of susceptible Gram-positive
bacteria. Hydrolysis of the cell wall results in the lysis of these bacteria. Chelating agents,
such as EDTA, have been reported to increase the sensitivity of Gram-positive bacteria
to lysozyme. Interestingly, lysozymes in nature often occur with natural chelating agents,
such as ovotransferrin in eggs and lactoferrin in tears and milk.63

501 Evolution and Challenges of Sustainability
Oxidoreductive enzymes catalyze reactions to produce products that frequently are
cytotoxic and have antimicrobial activity. The use of natural oxidoreductive enzyme
systems including lactoperoxidase plus glucose oxidase for product preservation have been
developed to achieve mild preservation in response to the perceived consumer need for
products that do not contain traditional preservatives.63 In the presence of glucose substrate
and oxygen, glucose oxidase produces hydrogen peroxide, which then becomes a substrate
for lactoperoxidase. Lactoperoxidase uses hydrogen peroxide and an oxidizable anion such as
thiocyanate as a substrate to produce hypothiocyanate, which is believed to target exposed
sulfhydryl groups in the bacterial cell membrane and inhibit bacterial metabolism.63
Although this is an elegant biochemical system for achieving antimicrobial action, it does
not seem to have gained wide acceptance for use in the cosmetic industry.
In recent years, there has been an increase in the promotion of fermented ingredients for use
as safe and natural preservatives. Leucidal® Liquid is a natural preservative derived from
radishes fermented with Leuconostoc kimchii, a lactic acid bacterium that has traditionally
been used to make kimchi. Promotional material indicates that Leucidal® Liquid consists
of an isolated peptide that is secreted by the bacteria during the fermentation process. It is
likely that the peptide is a bacteriocin—a peptide antibiotic that may kill Gram-positive
bacteria by disrupting cell wall production and cell membrane functions.64 Leuconostoc spp.
are heterofermentative lactic acid bacteria, which produce lactic acid and lesser amounts of
acetic acid, ethanol, and carbon dioxide during fermentation. It is believed that the primary
antimicrobial action of this ferment would be due to the short-chain fatty acids, ethanol, and
bacteriocins. Leuconostoc/radish root ferment filtrate is a natural ingredient derived from
the fermentation of radish roots with Leuconostoc spp., resulting in a natural preservative with
antimicrobial peptides that are reported to target bacteria and fungi. The radish roots may
provide somewhat different substrates than radishes used for the Leucidal® Liquid, and this
may result in different fermentation products. However, it is likely that the antimicrobial
action of the Leuconostoc/radish root ferment filtrate would be like that of the Leucidal®
Liquid. Water/punica granatum fruit extract/Lactobacillus ferment is a preservative obtained
from Lactobacillus spp. fermentation of pomegranate (Punica granatum). The Lactobacillus spp.
used may be homofermentative, which means that it produces virtually only lactic acid
during fermentation, or it may be heterofermentative. The strain used may also produce
bacteriocins. It is likely that short-chain fatty acids and bacteriocins (if present) would be
responsible for preservative action at recommended use levels up to10% in formulations.
Saccharomyces/rice ferment filtrate is advertised to balance the skin’s microbiome, strengthen
the skin barrier, and improve moisture retention. Saccharomyces spp. is yeast. This ferment
is reported to contain essential minerals, amino acids, β-glucan and vitamins. The amino
acids may provide nutrients for the skin microflora. Yeast (1→3)-β-glucan is a biological
response regulator that is involved with activation of various immune cells, including
macrophages and neutrophils, resulting in increased production of interleukins, cytokines,
and antibodies that stimulate the immune system to prepare the body to better fight
against infection.65 Promotional materials indicate that it works by preserving the skin’s
natural microbiome balance.
THE SKIN MICROBIOME
The skin is the largest organ in the human body, and it provides an epithelial interface that
separates the body from the external environment. The skin helps maintain homeostasis