The chemistry of passion fruit

Introduction

The passion fruit is a native of tropical America and was noted by the Spanish in Brazil in the 1500's. There are more than 500 species of which at least 50 or more are edible.

The two main commercial varieties are Passiflora edulis L. a purple fruit and P. edulis f. flavicarpa a yellow variety.
Brazil is the largest producer of passion fruit in the world with more than 35,000 ha under cultivation providing 485 thousand tons of fruit. The yellow passion fruit is the most important species cultivated in Brazil, corresponding to 95% of the planted area.
Australia and Brazil are the largest markets for passion fruit where the bulk is used for blending with other juices and in softdrinks.

Blossom of passion fruit yellow passion fruit

Chemistry

Sugars

The total carbohydrate content is around 15-20 % with slight variations between the purple and yellow varieties.
The breakdown (in percent) is given as:

  fructose glucose sucrose
purple 33.5 37.1 29.4
yellow 29.4 38.1 32.4

with a trace of 7 others.

Acids

Both yellow and purple have a high acid content (pH around 3) and the breakdown has been given as:

meq/100g citric acid malic acid lactic acid malonic acid succinic acid ascorbic acid
purple 13.1 3.86 7.49 4.95 2.42 0.05
yellow 55 10.55 0.58 0.13 trace 0.06

The sugar/acid ratio is sometimes used as a measure of sweetness and there is a significant difference between the purple and yellow varieties, 5:1 compared to 3:8, so that the purple is generally considered to be sweeter.

Pigments

In 1963, it was determined that the colour of the passion fruit was not due to anthocyanins and only trace amounts of flavones were found as well.
In 1972, further work identified the major carotenoid pigments in the purple variety, which included:

Alkaloids

In 1975, 7 alkaloids were detected and 4 were identified as harman(e), harmol, harmin and harmalin. Pharmacological tests showed that the juices had slight sedative effects.
Harman(e) (CAS 486-84-0, Molform= C 12 H 10 N 2) is shown below.

Volatiles

By 1972, over 165 compounds had been detected in the volatiles of the juice of the yellow variety. The highest quantities being C2-C8 esters of the C2-C8 fatty acids. Other volatiles included the degradation products of carotenoids, sulfur-containing components and some unusual aliphatic esters.

D.J. Casimir and F.B. Whitfield in 1978 introduced the concept of the "flavour impact value" and from the over 300 volatile flavour components that they detected, identified 22 as having passion fruit flavour. Using linear regression methods they were able to reproduce the natural flavour by combining 15 of these volatiles and calculated each chemicals contribution to the flavour profile.

Flavour-Impact Values

Compound Flavour
impact value		 Concentration
in juice (ppm)		 Contribution
to flavour
profile(%)
6-(but-2'-enylidene)
1,5,5-trimethylcyclohex-1-ene		 79 1.1 30
(Z)-hex-3-enyl butanoate 41 0.8 11
hexyl butanoate 6.8 4.1 9
ethyl (Z)-oct-4-enoate 62 0.4 8
β-ionone 410 0.05 7
edulan I 23 0.8 6
ethyl (Z)-octa-4,7-dienoate 239 0.06 5
Linalool 30 0.05 5
Ethyl hexanoate 1.3 7.6 3
heptan-2-ol 1.7 5.3 3
(Z)-hex-3-enol 26 0.3 3
S compounds 76 0.1 3
hexanol/ nonan-2-one 1.8 4.0 3
Rose oxide 45 0.2 2
methyl butanoate 0.7 8.3 3

A simulated GC of the headspace vapours of yellow passionfruit is available as a JSmol display.
A fascinating distinction between the yellow and purple passionfruit was found on studying the presence of chiral compounds. For example, heptan-2-ol from the purple was found to be 92% (R) while in the yellow it was 82% (S)-enantiomer. This suggested that different pathways and/or enzymes were involved in their formation.

References

"Tropical Fruit Processing", Edited by J. Jagtiani, H.T. Chan, Jr. and W.S. Sakai, Food Science and Technology, A series of monographs, 1988, Academic Press, Inc., 1250 Sixth Avenue, San Diego, California, 92101.
"Food Flavourings", Edited by P.R. Ashurst, Blackie Academic & Professional, an imprint of Chapman & Hall, Wester Cleddens Road, Bishopbriggs, Glascow, G64 2NZ, UK. 2nd edit. 1995.
"Volatile compounds in foods and beverages" , Ed by H. Maarse, Marcel Dekker, Inc, New York, 1991.
D.J. Casimir and F.B. Whitfield, Flavour impact values, a new concept for assigning numerical values for the potency of individual flavour components and their contribution to the overall flavour profile. In: Int. Fed. of Fruit Juice Producers Symp. Proc., Juris Verlag Zurich, Bern (1978), pp. 325-347.
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The Department of Chemistry, University of the West Indies,
Mona Campus, Kingston 7, Jamaica.
Created May 1997. Links checked and/or last modified 18th February 2014.
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