By refluxing tomato oleoresin in ethyl acetate for one week, the lycopene isomer profile could be improved, with the quantity of trans-isomers significantly increased, according to research published online in the journal Food Chemistry .
Lycopene is an antioxidant that is present in red- and pink-coloured fruits and vegetables.
As well as being used as a food colouring, it is also used in supplements.
The role of lycopene in heart health and in reducing the risk of certain cancers is supported by a body of research.
Red tomatoes typically contain about 95 per cent of their lycopene as the all-trans-isomer, reported to be the most stable form.
In tangerine tomatoes, on the other hand, the lycopene is also present as tetra-cis-lycopene, a geometric isomer of all-trans-lycopene.
Geometric isomers refer to two or more substances that have the same chemical make-up but the arrangement of the constituent elements is different, giving the substances different properties.
But evidence is mounting that the tetra-cis-lycopene form is more bioavailable to humans.
But the researchers report that there are 72 different types of cis-lycopene, with the so-called 5Z-, 9Z- and 13Z-lycopene usually predominating.
(The Z nomenclature is another, more complicated way of naming isomers.
Roughly, the Z form refers to cis, and E refers to trans).
"The physicochemistry and bioavailability of all-E- and Z-isomers of lycopene are known to be different," wrote lead author Pierre Lambelet.
"Lycopene Z-isomers have been described to be more bioavailable than the naturally occurring all-E-isomer."
"In addition, it has been demonstrated that Z-isomers of lycopene make up 50 per cent of the total lycopene in human serum and tissues.
For these reasons lycopene Z-isomers are regarded as having potentially higher health benefits than the all-E-isomer."
Process information The researcher started by investigation how lycopene isomerisation was affected by incubating the compound in various organic solvents or heating a lycopene-rich tomato extract.
According to these preliminary results, they found that heating the lycopene-rich extract in ethyl acetate produced successively 13Z-, 9Z- and 5Z-lycopene.
The longer the heating time, the less 13Z-lycopene was produced, said the researchers.
"Incorporating a long period of heating in ethyl acetate during the preparation of isomerised tomato extracts allows us to obtain a potentially active ingredient with good lycopene stability at room temperature both in terms of total lycopene content and lycopene isomer profile, which is a mandatory parameter for its further use in food products," they report.
Industrial importance "From an industrial perspective isomerising lycopene in tomato oleoresin by heating in ethyl acetate is much more convenient," wrote Lambelet.
"In fact isomerisation rather than degradation of lycopene occurred during heating in ethyl acetate."
"This way of isomerisation has the further advantage that ethyl acetate is already used by food ingredient manufacturers for the preparation of tomato extracts," he added.
"For that reason, extraction and geometrical isomerisation can be achieved in a single step."
Nestle research into lycopene Nestle is not new to lycopene research, and has produced a form of lacto-lycopene with high bioavailability, giving the company a patentable form of an existing nutrient.
This resulted is Nestlé's innéov lycopene supplement for skin health and beauty - the company's first and only move into dietary supplements, produced in collaboration with L'Oreal.
Source: Food Chemistry Published online ahead of print 23 May 2008, doi: "Improving the stability of lycopene Z-isomers in isomerised tomato extracts" Authors: P. Lambelet, M. Richelle, K. Bortlik, F. Franceschi, A.M. Giori