Yellow 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 400 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.
Australia is the largest single market for passion fruit and the bulk is used for blending with other juices and in softdrinks.
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, malonic, succinic, ascorbic acids

purple		13.1		3.86		7.49, 4.95, 2.42, 0.05
yellow		55.0		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 aside.

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.

Casmir and Whitfield in 1978 introduced the concept of the "flavour impact value" and from the over 300 volatile flavourants 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 volatile and calculated each chemicals contribution to the flavour profile.
Flavour-Impact Values

Compound			Flavour 	Concentration	Contribution
				impact value	in juice (ppm)	to flavour
								profile (%)
6-(but-2'-enylidene)		79		1.1		30
1,5,5-trimethylcyclohex-1-ene
(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
beta-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

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.

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

Created May 1997. Last modified 21st April-98.
URL http://wwwchem.uwimona.edu.jm:1104/lectures/psnfruit.html