On February 5, 1996 selected branches of Safeway and Sainsbury's supermarkets throughout the United Kingdom started to sell tomato purée made from genetically-modified tomatoes. It proved very popular with shoppers.
By July 1999, however, the product had been withdrawn. What was it, and how and why was it made?
A European first
Labels on both the cans clearly stated that the product had been made with genetically modified tomatoes. Although there was at that time no legal requirement to label the product, both supermarkets adopted an 'open' information policy from the start. This was the first time that food made from a genetically modified organism has been sold in Europe. For the inquisitive customer there was no shortage of information: leaflets were available describing the product and its benefits to the environment and consumer. Brief details of genetic modification and the regulatory processes through which the product has had to pass were also given.
According to the supermarkets, sales in the 80-odd stores in which supplies were initially available were brisk. Figures indicated that once they bought the product, shoppers came back for more. In November 1997, Safeway Stores announced that they had sold three quarters of a million cans of the product, and that average sales per store of the modified tomato purée exceeded those of the conventional equivalent. One reason might have been the price: the new purée cost 29 pence for 170 grams while the traditional form cost slightly more: 29 pence for a mere 142 grams.
Both supermarket chains pledged that the new product would always be offered alongside its old-fashioned counterpart. This move pleased consumer groups, which had no objection to the purée, provided that it was deemed safe to eat by the regulatory authorities and that consumers were always given a choice.
However, commercial pressures generated by public concern about GM foods early in 1999 forced Sainsbury's to announce that it would withdraw the product from sale. Stocks were exhausted by July 1999.
There has been great confusion about the tomato purée, which was produced by the British firm Zeneca Seeds (subsequently part of Syngenta). Many so-called 'experts' regularly confused it with the Calgene Flavr Savr, an unrelated type of fresh tomato that was sold only in the USA (see below). A particularly inaccurate and misleading article even appeared in the scientific journal Nature in April 1999 (Nature 398, pages 651-656).
Why was the tomato developed?
Tomatoes are one of the world's most important crops by virtue of the volume produced (70 million tonnes world wide in 1993) and their contribution to our nutritional needs. Conventional breeding procedures have generated improved tomato varieties with acceptable flavour and handling qualities for the fresh fruit and appropriate rheological characteristics for processed products. However, fresh tomatoes still do not fully meet consumer expectations in terms of flavour and the food industry constantly seeks improvements in processing characteristics.
Therefore novel approaches have been sought through the use of DNA technology to accelerate the introduction of new tomato varieties. Research has been aimed at understanding the complexities of the ripening process at the molecular level and at developing methods for the modification of tomato quality.
Several research groups have given this their attention but not only with the aim of producing a better tomato. Indeed the overall purpose was to gain a better understanding of ripening processes in general by studying the tomato, which is a relatively easy fruit on which to work. It was expected that benefits gained would be transferable to other fruit and vegetable crops including apples, bananas, mangoes, melons, nectarines, sweet peppers, peaches, pineapples and strawberries.
The outcome has been the isolation of a large number of genes which are expressed either exclusively or preferentially in the ripening and ripe tomato. Some of the genes (effect genes) were expected to have relevance to the major targets identified by the tomato industry, that is: viscosity, handling characteristics, soluble solids, colour and taste.
Professor Don Grierson led one of these research groups. It began work in the mid-1970s at the University of Nottingham and then began a collaboration with the (then) British firm Zeneca Seeds. Improved methods were developed for the modification of the expression of genes during plant growth and development. Recombinant DNA techniques were used to introduce into the plant genome shortened PG genes that are not translated into a functional protein. With this approach improvements in tomato texture were obtained by inhibition of enzymes involved in cell wall metabolism.
Reduced enzyme activity
Cellulose, hemi-celluloses and pectins are cell wall components which contribute to textural characteristics. The research focused on the enzymes which are responsible for modifying pectins during normal tomato development. One such enzyme is polygalacturonase (PG), a pectinase, which hydrolyses the alpha-1,4 linkages in the polygalacturonic acid component of cell walls. Pectin esterase (PE) is also involved in pectin modification.
The PG enzyme is synthesised only during ripening of the tomato and is found within the cell wall compartment of pericarp cells. The function of PG during the natural ripening process is to break down the pectin of the middle lamella of the fruit cell wall, thereby causing the fruit to soften. The gene encoding PG was cloned. Tomatoes modified with a shortened PG gene were found to have only 1% of the residual levels of the PG activity of the unmodified fruit and, consequently, pectin of a considerably greater chain length. Moreover, the composition of low PG, genetically modified fruit was otherwise indistinguishable from that of the unmodified tomato. Thus it became possible to slow the natural softening process of ripening without interrupting development of desirable flavour and colour. This can benefit tomato processing by providing an opportunity to produce sauces, ketchups and purées with the desired thickness because of retention of high levels of pectin.
Modified tomato lines were grown under semi-commercial conditions in glasshouses and their value for processing was assessed. An increase of 80% in a measure of viscosity which reflects tomato paste yield potential was obtained in the low PG tomato lines. Other work indicated their value also in producing tomato juice with improved processing characteristics. Regarding low PE tomatoes, assessments indicate that the major effect of PE reduction is to increase serum viscosity which enhances the glossy appearance of the tomato purée.
In 1989 the work moved on to field scale trials in Chile and California in a collaboration between Zeneca and the Peto Seed Company which successfully achieved its aim of generating genetically improved hybrids for the tomato processing industry for use on a commercial scale.
The outcome was a tomato purée with the desired rheological properties. There were also production cost advantages through a reduced need for heat treatment both to reduce PG activity and, as the modified fruit contains less water, to concentrate the purée before canning. Another cost benefit came from there being less wastage of the firmer fruit by damage during transport. The reduced heat treatment also provided better retention of natural flavour compounds and contributed to conservation of energy resources.
As the tomato was produced using genetic modification, it is a legal requirement for the product to be subjected to extensive review by the appropriate regulatory authorities before being given approval for sale in the UK. The tomato was grown in California because the British climate is unsuitable. However, the whole tomato could not be marketed in Europe because, as a viable GMO (genetically modified organism), marketing consent would be needed under European Directive 90/220/EEC.
The Flavr Savr
Researchers at Calgene in Davis, California, working for the Campbell Soup Company, made use of a different DNA technology ('antisense' technology) to produce similar effects. The antisense gene's mRNA binds to the normal mRNA and in so doing 'silences' the gene. The modified tomatoes produced only 1% of the normal amount of the enzyme polygalacturonase, so the fruit did not soften so fast as they ripened.
Calgene's modified tomato was dubbed the Flavr Savr, the name which was also given to the patented antisense gene. The name reflects the improved taste of the tomatoes, which, because they could be left on the plant until fully-ripened, tasted better than tomatoes which were picked when green and ripened artificially (a common practice in the USA, although not in Europe).
In May 1994 the Flavr Savr was cleared by the US Food and Drug Administration for sale to US consumers. This was the first fresh genetically-modified fruit or vegetable to be sold in the world. Permission to sell the fruit in Canada and Mexico was also obtained in 1995. Calgene eventually marketed the tomatoes under the MacGregor brand name, and they were sold in over 3,000 stores throughout the western United States. Although the Flavr Savr was subsequently cleared for sale in the UK, provided that it was labelled, it could not have been sold there without European marketing consent. However, before this could be considered (a process which would have taken about 2 years) the tomato was withdrawn from production. During the scale-up in commercial production, unacceptably low yields were obtained. The Flavr Savr tomato is no longer produced.
Read all about it
Read about the development of the US Flavr Savr tomato in an account by Calgene insider Belinda Martineau.
First fruit by Belinda Martineau (2002) McGraw-Hill Education, London. ISBN: 0 0714 0027 3 (Paperback, 224 pages).
Despite inaccurate press reports to the contrary, the GM tomato purée was never used in anything in the UK but the Sainsbury's and Safeway's tinned products. The ketchup shown above was produced solely as a promotional item by Zeneca Seeds.