F- 1. Fructose in acidic media to hydroxy methyl furfural
F- 2. Condensation of hydroxymethyl furfural to form cirsium
aldehyde ( 5, 5’-oxy-dimethylene-BIS)2-furaldehyde
Ioften take the opportunity to examine the fresh botanical to compare the commercial essential oils. Pink grapefruit proved no exception. During my last trip to Florida I picked up some pink grapefruit from
Indian River, a well-known and respected area for
delicious pink grapefruit.
Grapefruit has a very distinctive fragrance and
flavor. Pink grapefruit has the additional allure
of being light pink to Ruby red, which stimulates
another of our keenest senses, sight. It is well known
that color can influence our perception of flavor and
fragrance and that is why professional panelists are
often prevented from experiencing any color at all
during sensory panel evaluations.
I am perpetually interested in the qualitative as
well as quantitative differences between the essential oils that are normally used in our industry – as
opposed to fresh fruit peel and commercial juice
extracts, which often fail to capture the fresh character of the botanical.
I promptly extracted the peel and juice with methylene chloride and prepped the samples for GCMS
analysis. In addition, I examined the juice directly
(without extraction) as I am aware that much of the
important flavor and fragrance components are in
the water (not the peel) section, which exhibit significant olfactory and flavor differences. This had a few
analytical surprises that we shall see a bit later.
Additionally, it should be noted that while grapefruit and grapefruit juice are known to be bitter,
the bitter flavor does not come from the fruit itself,
but the surrounding albedo and section casing very
likely from naringen and other flavenoids present in
large quantities. If one carefully removes the peel,
as well as the skin encasing the sections, one might
be pleasantly surprised at how sweet the fruit is and
completely devoid of the characteristic bitter flavor
that one experiences with grapefruit juice. This
might be one of the reasons that grapefruit juice has
always taken a back street to orange juice which is
much more preferred and consumed in much larger
quantities. This of course, affects supply and pricing
– basic economics.
Component differences in juice
The first thing that appears as revelatory is the
stark contrast between the directly-injected juice and
the juice extract. A bit of reflection and understanding of what happens in an injection port (250 °C) and
a bit of literature research helps explain this huge
These results do not indicate the true nature of
the juice as it is but points to the reason processed
juices are drastically different in character
Image courtesy of author.
When fructose is heated in an acidic medium, the
fructose is transformed into hydroxymethyl fufural
(HMF) (See F- 1) 2.
The other major component, cirsium aldehyde is
a condensation product of hydroxymethyl furfural
(see F- 2).
Major contributors in grapefruit juice
Many of the other components, both furfural
and furaneol, as well as other pyrones are formed
during this process. What is likely to be present in
the juice, (pre-reaction state) are acetaldehyde, acetic
and other acids which help promote the reactions.