|
GrapefruitA brief history of the
grapefruit is available from Univ. of Florida. |
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 are that by the year
2000, the total area planted in all varieties of citrus would be about 24,500 acres.
Ref: The Gleaner, Sat Dec 21st, A16, 1996.
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 | Amount in fresh orange juice |
FEMA code |
| Terpene hydrocarbons | ppm | ppm | |
| R(+)-limonene | 0.21 | 1-80 | (2633) |
| myrcene | 0.042 | 0.05-2 | (2762) |
| alpha-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 | 0.041 | 0.05-0.3 | (3203) |
| 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) |
| alpha-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).
"Volatile compounds in foods and beverages"
, Ed by H. Maarse, Marcel Dekker, Inc, New York, 1991.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, beta-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.
|
GrapefruitA brief history of the
grapefruit is available from Univ. of Florida. |
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 1-p-menthene thiol. |
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. |
|
LimesOne 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 contains 6-9% citrals whereas the distilled oil, 1-10%. citral-a (geranial) |
Use this link for an example of a GC Headspace analysis of a piece of lime skin.
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Created May 11th 1995. Last modified 13th October 1999.
URL http://wwwchem.uwimona.edu.jm:1104/lectures/citrus.html
