Jamaican Citrus

The 1996 citrus crop saw a total of 4.25 million boxes of all varieties of citrus being taken in, of which 2.2 million were consumed locally. Projections were that by the end of the year 2000, the total area planted in all varieties of citrus would be about 24,500 acres. (Sorry, this is well out of date!)
Reference: The Gleaner, Sat Dec 21st, A16, 1996.

Oranges

Quite a few varieties of orange are grown in Jamaica but very few studies have been done on their chemistry.
An interesting paper on the effect of storage on the constituents that affect the aroma of Valencia oranges was published by: C. Velez, E. Costell, L.Orlando, M.I. Nadal, J.M. Sendra and L. Izquierdo in J. Sci. Food Agric., 1993, 61, 41-46.
They took freshly squeezed oranges and split the juice into several fractions. Some was immediately frozen at -18C as a control, while the other samples were stored at 0, 20 and 35C for up to 3 months. They then looked at the variation of the aroma constituents as a function of storage.
Note that unlike grapefruit or lime, the volatiles in oranges that contribute to the flavour are many and varied.

**Some volatile compounds thought to impart orange flavour.**
Component	Flavour threshold ppm	Amount in fresh orange juice, ppm	FEMA code
Terpene hydrocarbons
R(+)-limonene	0.21	1-80	(2633)
myrcene	0.042	0.05-2	(2762)
α-pinene	1	0.02-0.09	(2902)
valencene	-	0.04-0.2
Aldehydes
acetaldehyde	0.022	3-7	(2003)
(E)-2-pentenal	0.15	<0.01	(3218)
n-octanal	0.0005	<0.01-0.3	(2797)
nonanal	0.0043	<0.01-0.04	(2782)
(cis)-4-decanal	0.0032	0.01-0.15	(3264)
citral-a or geranial, citral-b or neral	0.041	0.05-0.3	(3203)
β-sinensal, α-sinensal	0.0038	-
Esters
ethyl acetate	3.0	0.4	(2414)
ethyl propionate	0.005	0.1	(2456)
methyl butanoate	0.059	0.1
ethyl butanoate	0.00013	0.08-1.4
ethyl 2-methylbutanoate	0.0001	<0.01-0.1
ethyl 3-hydroxyhexanoate	-	0.14-1	(3545)
Alcohols
ethanol	53	380
(E)-2-hexen-1-ol	-	<0.01	(2562)
(E)-3-hexen-1-ol	0.07	<0.01-0.5
D-linalool	0.0038	0.15-2.34	(2635)
α-terpineol	0.3	0.09-1.1	(3045)

The numbers in brackets on the right are the FEMA codes (Flavor and Extract Manufacturers' Association of the USA).

References

"Volatile compounds in foods and beverages" , Ed by H. Maarse, Marcel Dekker, Inc, New York, 1991.

Structures with Citrus-like Flavours

Over 450 aliphatic and isoprenoid substances have been isolated from the most common citrus fruits in studies carried out around the world.
Some examples include:
n-Decanal, β-Sinensal, Citral, 3-Methyl oct-2-enal and (+)Nootkatone.
The essential oils of tangerine and orange can be extracted by bruising the peel of the fruit and collecting the oil exuded.
Some oils need special treatment, for example, lime oil needs boiling with water to bring out the best flavour.
The essential oils contain a proportion of oily substances which are unsaturated hydrocarbons such as terpenes, hemiterpenes and sesquiterpenes. Although these contribute considerably to the flavour of an oil they are usually found to be insoluble in water and alcohol. In a syrup or cordial they tend to separate or float to the surface which may give an objectionable tart taste in the mouth.

Grapefruit

See an exerpt from: "Fruits of warm climates- Mango" Morton, Julia F. 1987. p. 221- 239., Miami, FL. at about the grapefruit.

A pink grapefruit for breakfast anyone?

The constituent that gives the characteristic flavour of grapefruit is reported to be nootkatone, shown below.

This has a fresh, green, sour, fruity character with a threshold value of 0.8 ppm. Its optical antipode (-)nootkatone, has no fruity character at all and its threshold value is about 600 ppm.

Another character imparting terpene found in grapefruit is sometimes called grapefruit mercaptan, or 1-p-menthene thiol.

Some of the important flavour components in grapefruit

Compound	Concentration (ppm)	Relative Flavour contribution
limonene	86	376
acetaldehyde	1.45	167
decanal	0.49	100
nootkatone	6	8
ethyl acetate	16.2	1906
methyl butanoate	4.2	278
ethyl butanoate	10	9091
1-p-menthene-8-thiol	2.00E-05	not determined

Grapefruit juice contains citrus flavonoid compounds not found in other citrus juices. The most prevalent of these is naringin which produces the characteristic bitter taste that orange juice does not have. The structure is given below.

Limes

One of the first trees to be planted by Jamaicans when they move into a new house is the lime tree,

so there are always plenty of limes around for a cool refreshing drink.
Cold, hand pressing of the peel gives only a mild lemon-like flavour, however if the fruit is mashed and the oil steam-distilled then a strong lime flavour is obtained, although some of the citral is decomposed during this process.
The pressed oil generally contains significantly more citrals than the distilled oil.


citral-a (geranial)

**Volatiles in lime oil**
Compound	oil-juice emulsion (area %)	distilled oil (area %)
α-thujene	0.36	0.02
α-pinene	2.23	1.19
sabinene	3.04
β-pinene	19.95	2.23
δ-3-carene + 1,4-cineole	0.02	1.96
α-terpinene	0.17	2.53
p-cymene	0.62	1.79
d-limonene + 1,8-cineole	50.01	48.86
g-terpinene + octanol	7.10	10.91
terpinolene + nonanal	0.41	7.76
linalool	0.15	0.05
α-fenchol		0.66
terpinen-1-ol		0.84
β-terineol		0.69
borneol		0.42
citronellal	0.03
terpinen-4-ol	0.22	0.80
α-terpineol	0.26	6.26
decanal	0.20
γ-terpineol (?)		0.04
neral	1.43	0.02
geranial	2.36	0.04
undecanal	0.03
neryl acetate + unknown	0.47	0.12
geranyl acetate	0.28	0.08
dodecanal	0.11

Use this link for an example of a GC Headspace analysis of a piece of lime skin.
A survey of phenolics including flavonoids in citrus fruit has been reported by the US, Department of Agriculture.

Reference

"Volatile compounds in foods and beverages" , Ed by H. Maarse, Marcel Dekker, Inc, New York, 1991.

Return to links to the chemistry of other Jamaican items, including spices and fruit and vegetables.

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Created and maintained by Prof. Robert J. Lancashire,
The Department of Chemistry, University of the West Indies,
Mona Campus, Kingston 7, Jamaica.

Created May 11th 1995. Links checked and/or last modified 8th August 2014.
URL http://wwwchem.uwimona.edu.jm/lectures/citrus.html