Wax Ester
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A wax ester (WE) is an
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
of a
fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...
and a fatty alcohol. Wax esters comprise the main components of three commercially important waxes:
carnauba wax Carnauba (; pt, carnaúba ), also called Brazil wax and palm wax, is a wax of the leaves of the carnauba palm ''Copernicia prunifera'' (synonym: ''Copernicia cerifera''), a plant native to and grown only in the northeastern Brazilian states of ...
,
candelilla wax Candelilla wax is a wax derived from the leaves of the small Candelilla shrub native to northern Mexico and the southwestern United States, '' Euphorbia antisyphilitica'', from the family ''Euphorbiaceae''. It is yellowish-brown, hard, brittle, a ...
, and
beeswax Beeswax (''cera alba'') is a natural wax produced by honey bees of the genus ''Apis''. The wax is formed into scales by eight wax-producing glands in the abdominal segments of worker bees, which discard it in or at the hive. The hive workers ...
.. Wax esters are formed by combining one fatty acid with one fatty alcohol: :RCOOH + R'OH <=> RCOOR' + H2O Various types of wax esters exist. Some are
saturated Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry * Saturation, a property of organic compounds referring to carbon-carbon bonds ** Saturated and unsaturated compounds **Degree of unsaturation ** Saturated fat or fatty ac ...
, and others contain unsaturated centers. Saturated wax esters have higher melting points and are more likely to be solid at room temperature. Unsaturated wax esters have a lower melting point and are more likely to be liquid at room temperature. Both fatty acids and fatty alcohols may be made of different carbon chain length. In the end, there are many different possible combinations of fatty acids and fatty alcohols and each combination will have a unique set of properties in terms of steric orientation and phase transition. The chain lengths of fatty acids and fatty alcohols in naturally occurring wax esters vary. The fatty acids in wax esters derived from plants typically range from C12-C24, and the alcohols in plant waxes tend to be very long, typically C24-C34. The fatty acids and fatty alcohols of wax esters from different marine animals show major differences. Wax esters of sperm whales contain C12 fatty acids and C14 fatty acid and alcohols. Monounsaturated C18 is the dominant fatty acid of most fish wax esters, with the exception of roe wax esters, which have sizeable amounts of polyunsaturated fatty acids such as 20:5n-3, 22:5n-3 and 22:6n-3. The fatty acids of wax esters of certain
zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
largely reflects the fatty acids of
phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...
, and contain high amounts of C14 and C16, as well as 20:5n-3, 22:5n-3 and 22:6n-3 and monounsaturated C20 and C22 are the principal fatty alcohols.


Natural sources

Beeswax is 70–80% wax esters. These esters are derived from C12-C20 fatty acids. The remaining content of beeswax are wax acids (>C20) and paraffins. In 1976, an estimated 10,000–17,000 tons were harvested. The primary use was in candles. The esters in carnauba wax consist of ca 20% cinnamic acid derivatives, which may be related to the hardness of this wax.


Other, minor wax esters

Wax esters are commonly found in
shellfish Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater envir ...
and as a part of the cuticle of
arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
s. In leaves, they prevent loss of water. Nuts from
jojoba Jojoba (; botanical name: ''Simmondsia chinensis'')also commonly called goat nut, deer nut, pignut, wild hazel, quinine nut, coffeeberry, and gray box bushis native to the Southwestern United States. ''Simmondsia chinensis'' is the sole specie ...
store as much as 50% of wax esters. These wax esters, which are monounsaturated, are very similar to sperm oil. Marine organisms like
dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
s,
pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s, and fishes store low-density wax esters in their swim bladders or other tissues to provide
buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the p ...
. Wax esters ''per se'' are a normal part of the diet of humans as a lipid component of certain foods, including unrefined whole grain cereals, seeds, and nuts. Wax esters are also consumed in considerable amounts by certain populations that regularly eat fish roe or certain fish species. That said, wax esters are not typically consumed in appreciable quantities in diets containing many processed foods.


Metabolism

Lipase Lipase ( ) is a family of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; however, these are usually tr ...
s and carboxylesterases that hydrolyze
triglycerides A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as we ...
have demonstrated enzymatic activity towards wax esters. Kinetic data show that
EPA The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
and
DHA DHA, Dha and dha may refer to: Chemicals * Docosahexaenoic acid, a 22:6 omega-3 fatty acid * Dehydroandrosterone, an endogenous androgenic steroid * Dehydroascorbic acid, an oxidized form of ascorbic acid * Dehydroacetic acid, a pyrone derivati ...
provided as wax esters reaches a maximal concentration at approximately 20 h post-consumption, and may indicate delayed absorption of the fatty acids.


Bioavailability

There has been a common understanding that wax esters are poorly absorbed by humans, partly due to outbreaks of the purgative effect named keriorrhea, associated with consumption of
oilfish The oilfish (''Ruvettus pretiosus'') is a species of snake mackerel fish with a cosmopolitan distribution in tropical and temperate oceans. It can be found at depths of from , usually between . It can grow to a length of TL (nearly 10 feet) ...
(''Ruvettus pretiosus)'' and
escolar The escolar, ''Lepidocybium flavobrunneum'', a species of fish in the family Gempylidae, is found in deep (200–885 metres, or 656–2,904 ft) tropical and temperate waters around the world. It is also known as snake mackerel, ' ( Hawaii ...
(''Lepdocybium flavobrunneum)''. Fillets from these fish species contain up to 20% fat, where 90% of the fat comes as wax esters, resulting in a typical intake of more than 30 000 mg wax esters from one single meal.
Orange roughy The orange roughy (''Hoplostethus atlanticus''), also known as the red roughy, slimehead and deep sea perch, is a relatively large deep-sea fish belonging to the slimehead family (Trachichthyidae). The UK Marine Conservation Society has categori ...
(''Hoplostethus atlanticus)'' is an attractive food fish with 5.5% fat, where 90% of the fat comes as wax esters. Consumption of this fish gives no unpleasant adverse effects, most likely due to the relatively low fat content that provides approximately 10 000 mg wax ester per 200 grams serving of fish. In 2015 a randomized, two-period crossover human study, showed that EPA and DHA from oil extracted from the small crustacean ''
Calanus finmarchicus ''Calanus finmarchicus'' is a species of copepods and a part of zooplankton, which is found in enormous amounts in the northern Atlantic Ocean. Distribution and ecology ''Calanus finmarchicus'' is most commonly found in the North Sea and the N ...
'' was highly bioavailable and the study concluded that oil from ''C. finmarchicus'' could serve as a relevant source of the healthy omega-3 fatty acids EPA, DHA and SDA. 86% of the oil from ''C. finmarchicus'' comes as wax esters. Studies on mice have shown that, despite consuming diets containing similar amounts of EPA and DHA, blood levels of both EPA and DHA were significantly higher in mice fed a diet supplemented with oil from ''C. finmarchicus'' compared to those fed an EPA+DHA ethyl ester enriched diet. Furthermore, oil from ''C. finmarchicus'' has been observed to have beneficial effects on obesity-related abnormalities in rodent models of diet-induced obesity at EPA and DHA fatty acid concentrations considerably lower than the concentrations used in similar earlier studies using other sources of EPA and DHA. Taken together, based on the available ''in vitro'' data, animal data, and the findings of the Cook et al. study demonstrating that circulating concentrations of EPA and DHA remained elevated up to 72 h after a single serving of 4 g oil from ''C. finmarchicus'' the hydrolyzed products of wax ester digestion are most likely slowly absorbed ''in vivo''.


Role as a nutrient

Marine wax esters have become a focus of attention due to documented positive effects on widespread medical conditions related to certain diets.  Harvesting on a lower trophic level on short-lived organisms would be more sustainable and the products would be less prone to environmental toxins and pollutants. Wax ester-based products from the small crustacean ''Calanus finmarchicus'' have been commercialized and sold by the Norwegian company Zooca.


See also

*
Keriorrhea Keriorrhea is the production of greasy, orange-colored stools which results from the consumption of indigestible wax esters found in oilfish and escolar. See also * Steatorrhea * Rectal discharge Rectal discharge is intermittent or continu ...


References


Further reading

*{{cite web, url=http://nzic.org.nz/ChemProcesses/animal/5E.pdf, title=Studies on Wax Esters in Fish, author=D. Buisson and S.F. Hannan, publisher=New Zealand Institute of Chemistry, access-date=2012-07-10 Esters