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

502 JOURNAL OF COSMETIC SCIENCE
by regulating temperature, preventing water loss from the body, reducing irritation/
injury due to harsh chemicals and harmful radiation, enabling touch and pain sensations,
supporting vitamin D synthesis, and preventing infection. The skin surface and appendages
are colonized by a diverse community of microorganisms, the “skin microbiome,” and
these microorganisms are involved with maintaining the skin ecosystem with their lipid
metabolism, colonization resistance to transient and pathogenic organisms, regulation of
the skin immune system (SIS), and creation of acid mantle condition of skin.66-69
The skin microbiome is composed of bacteria, yeasts, fungi, viruses, micro-eukaryotes
(mites), and archaea. Although the average number of microorganisms isolated from skin
using traditional culture methods (e.g., plating on agar media) ranges from 103–104 cfu/cm2,
humid places on the body, such as armpits, groin, and nostrils, may have microbial counts
exceeding 106 cfu/cm2. The microbial counts on the scalp, forehead and around the ears are
about 106 cfu/cm2, while microbial counts on the upper back, chest and arms range from
104–105 cfu/cm2.67,69,70 In 2016, Patra. Byrne and Wolf reported that 23–100% of healthy
people have dust mites, which generally are found on the face, around sebaceous glands,
and in hair follicles.71 Consequently, they are part of the normal microflora. Demodex mites
(Demodex folliculorum and Demodex brevis) are present on skin and may be associated with
rosacea and blepharitis.71
In the 2009 landmark publication by Grice et al., it was reported that skin sustains
microorganisms that influence human health and disease.72 They observed that traditional
culture-based characterizations of the skin microflora are biased toward species that readily
grow under standard laboratory conditions, such as the staphylococci, and that molecular
approaches have revealed a greater diversity of skin microflora in distinct topographical
regions of the skin. This provided the basis for examining multiple skin sites with the use
of genomic techniques.
Grice and coworkers analyzed 16S ribosomal RNA (rRNA) gene sequences from 20 distinct
skin sites of 10 healthy human test subjects and found that comparable sites on different
people harbor similar bacterial communities. Although the number of people being tested
was rather small, it was determined that 90% of the bacteria on skin could be classified
into four types (phyla): Actinobacteria (52% Gram positive bacteria with high (55%)
guanosine plus cytosine (G+C) DNA that include Corynebacterium, Actinomyces, Arthrobacter,
Micrococcus, Mycobacterium, Nocardia, Propionibacterium (Cutibacterium) and Rhodococcus
genera), Firmicutes (24% Gram positive bacteria with low G+C DNA content that include
Staphylococcus, Lactobacillus, Streptococcus, Clostridium and Bacillus genera), Proteobacteria
(16% Gram-negative bacteria that include Escherichia, Pseudomonas, Salmonella, Vibrio and
Helicobacter genera) and Bacteroidetes (6% Gram-negative rod-shaped bacteria that include
Bacteroides and Porphyromonas genera). Grice and coworkers found that coagulase negative
staphylococci (CNS) such as Staphylococcus epidermidis, along with Cutibacterium acnes
(formerly Propionibacterium acnes), Corynebacterium spp., Micrococcus spp., Streptococcus spp.,
and Acinetobacter spp. were the dominant genera present on skin.72 Many of bacteria in these
genera were found in studies of skin microflora reported by Samaras and Hoptroff in which
they estimated that Cutibacterium, Staphylococcus, and Corynebacterium genera constituted up
to 80% of the entire skin microbiome.73
Grice and coworkers noted that about 4% of the skin microbiome is represented by the
archaea, based on 16S rRNA sequencing.72 Archaea is a domain of single-celled organisms
that lack cell nuclei and are therefore prokaryotic like bacteria. However, most archaea have
not been isolated by traditional microbiological methods and have been detected only by