499 Evolution and Challenges of Sustainability
HURDLE TECHNOLOGY: USE OF PHENOLIC ANTIOXIDANTS
Many phenolic antioxidants have antimicrobial action. Branen and Davidson reported that
systems containing multiple antioxidants or antioxidants used in combination with metal
chelators often demonstrate synergistic antimicrobial action.51 Butylated hydroxyanisole
(BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquinone (TBHQ), and propyl
gallate are the most common phenolic antioxidants used in food and cosmetic products.
BHA is the most effective antimicrobial of the phenolic antioxidants, and it is active against
bacteria, yeasts, and molds. Generally, Gram-positive bacteria are more susceptible to BHA
than Gram-negative bacteria, with growth inhibition being obtained with 25–50 mg/mL
for Clostridium botulinum, 50–400 mg/mL for S. aureus, 400 mg/mL for P. aeruginosa, and
10,000 mg/mL for Salmonella senftenberg.51 Davidson, Brekke, and Branen found that all
combinations of BHA, TBHQ, and potassium sorbate had synergistic antibacterial activity
against S. aureus and Salmonella typhimurium in Trypticase Soy Broth.52 However, Rico-Munoz
and Davidson found that as little as 1.5–3% corn oil virtually eliminated the antimicrobial
activity against five test organisms in microbiological media.53 These results illustrated that
lipids may decrease the effectiveness of phenolic antioxidants. Branen and Davidson noted that
the effect of pH on the antimicrobial activity of BHA was dependent on the microorganism
tested and they concluded that the greatest potential for use of phenolic antioxidants would
most likely be in combination with other antimicrobials as part of a preservative system.51
HURDLE TECHNOLOGY: USE OF FRAGRANCES AND AROMA CHEMICALS
Kabara noted that spices and essential oils have been used for product preservation.54
The active components in essential oils generally include alcohols, phenols, esters, acids,
aldehydes, and/or terpenes. Essential oils including caraway, cinnamon, eucalyptus, lemon,
and sandalwood have substantial antimicrobial activity, based on zone of inhibition assays.
In 1979, Strum formulated deosafe fragrances using combinations of aromatic chemicals
(e.g., decyl alcohol, citral, eugenol and cinnamaldehyde) and essential oils with antimicrobial
activity (e.g., thyme, clove, and spice oil).55 Deodorancy may be obtained by use of
fragrances that mask offensive odors (e.g., axillary odor), such as natural oils that may have
antimicrobial/deodorant activity (e.g., citronellol, citral, hexyl cinnamal, limonene, linalool,
hydroxycitronellal, geraniol, eugenol, etc.),56,57 or by use of multifunctional ingredients that
have (or enhance) antimicrobial action (e.g., propylene glycol, dipropylene glycol, butylene
glycol, propanediol, BHT, methylheptylglycerin, C12-15 alkyl benzoate, tetrasodium EDTA,
etc.). Houstein et al. developed a deosafe fragrance containing farnesol, glyceryl monolaurate,
and phenoxyethanol that killed corynebacteria associated with axillary malodor.58 Aroma
chemicals have varying degrees of antimicrobial activity for different microorganisms, so
the most prudent use of these multifunctional ingredients may be as part of the preservative
system of a product. A comprehensive discussion of the use fragrances and aroma chemicals
for preservation may be found in the review by Kabara.54
HURDLE TECHNOLOGY: USE OF BOTANICALS
There is a growing interest in using natural extracts from plants as alternatives for synthetic
ingredients because they have antimicrobial synergy with other formula ingredients, they
are considered safe, they often have antioxidant and antibacterial properties, the emerging

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