Benoit Roger, Ph. D.
If you have the chance to visit Morocco or Tunisia during spring, get away from urban centers and follow your nose, it will probably lead you near one of the many plantations of bigarade orange or bitter orange spread in all Maghreb. From march to april, these little trees dress up with a myriad of white flowers, both fleshy and exquisitely perfumed. These flowers have been picked up by hand for generations and are immediately distilled to yield the precious Neroli essential oil and the corresponding hydrosol called orange blossom water. Hydrosols are sometimes (wrongfully) considered as a by products of essential oil production but for orange blossom water, it’s not the case. Orange flower water is a part of the locale culture. It is widely used in the famous north african pastries as well as in cosmetics and in aromatherapy for its soothing properties. Orange blossom flower water must contain at least 0.3 g/L and preferably 0.5-0.6 g/L of aromatic fraction to be considered as a true hydrosol. Here are the main compounds the aromatic fraction contains (Figure 1).
Fig. 1 : Compounds identified in orange blossom water from Morocco with minimum and maximum concentration (V. Jeannot and al., 2005).
|Compounds||Lowest concentration (% m/m)||Highest concentration (% m/m)|
|Phenyl ethyl alcohol||0.5||5|
Most of these compounds are frequently encountered in many other hydrosols and essential oils, but three of them are quite rare: benzyl nitrile (also called phenylacetonitrile), methyl anthranilate and indole. These nitrogen containing compounds are not very concentrated but they are very important in the distinctive scent and aroma of orange blossom water.
If you are familiar with orange blossom water, you may have noticed that the hydrosol sometimes takes an orange color. This has nothing to do with any pigment from the plant’s fruits. It is due to the polymerization of indole into several compounds including turbomycin A (Figure 2), an orange carbocation known for its antibiotic properties (D.E. Gillespie and al., 2002). This polymerization occurs when orange blossom water is exposed to sunlight (B. Roger and al., 2015).
By the way, the presence of this carbocation in orange blossom water also show that in some specific cases, GC do not allow to ”see” everything an hydrosol or an essential oil contain. Turbomycin A is not volatil but has a specific UV-Visible spectrum (maximum absorbance at 470 nm giving the orange color). It cannot be studied with GC but can easily be with HPLC (liquid chromatography).
In conclusion, hydrosol of Neroli is a great product to discover with an interesting aroma. The figure 3 shows what colors can be the hydrosol of Neroli in a different state of time. Surprising, isn’t it?
X. Fernandez, C. André, A. Casale., Hydrolats et eaux florales vertues et applications, 2015, Editions Vuibert. ISBN: 978-2-311-40003-8
V. Jeannot, J. Chahboun, D. Russell, P. Baret, Quantification and determination of chemical composition of the essential oil extracted from natural orange blossom water (Citrus aurantium L. ssp. aurantium), Int. J. Aromather., 2005, 15, 94–97. DOI: 10.1016/j.ijat.2005.03.012. URL: http://www.sciencedirect.com/science/article/pii/S096245620500024X
B. Roger, P. Burger, P. Baret, J. Chahboun, S. Cerantola, X. Fernandez & V. Jeannot, Identification of antibiotic and antiproliferative compounds in natural orange blossom water, J. essent. oil res., 2015, 28 (2), 89-95. DOI: http://dx.doi.org/10.1080/10412905.2015.1107646. URL: http://www.tandfonline.com/doi/full/10.1080/10412905.2015.1107646
D.E. Gillespie, S.F. Brady, A.D. Betterman, N.P. Cianciotto, M.R. Liles, M.R. Rondon, J. Clardy, R.M. Goodman and J. Handelsman, Isolation of antibiotics turbomycin A and B from a metagenomic library of soil microbial DNA. Appl. Environ. Microbiol., 2002, 68, 4301-4306. DOI: 10.1128/AEM.68.9.4301-4306.2002. URL: http://aem.asm.org/content/68/9/4301.short