IMPROVING THE QUALITY OF PROCESSED TOMATO PRODUCTS THROUGH THE GENETIC MODIFICATION OF FRUIT

Despite the effort of the tomato breeding companies, fresh tomatoes do not bear the expected high quality flavour consumers desire and could thus benefit from further improvements. In addition, improved processing characteristics (eg thicker juice) are sought by the food companies to stay competitive and provide flexibility during manufacturing. As traditional breeding is a slow process and the incorporation of multigenic traits is complex, novel approaches are required to accelerate the introduction of improved tomato varieties. The production of genetically modified tomatoes with improved processing characteristics offers such an opportunity (Schuch, 1994).

Tomato ripening is associated with a number of physiological and biochemical changes which affect quality. These include the biosynthesis and deposition of carotenoids in chromoplasts determining colour pigment production, the metabolism of sugars, volatiles and acids involved in flavour determination, and modifications to the structure and composition of the cell walls affecting fruit firmness and processing characteristics.

These qualitative changes are due to the action of specific enzymes whose expression is altered during fruit ripening.

To target these genes for quality improvement, the technique of genetic modification has been used. Genetic modification involves the introduction of these so-called quality genes into the plant genome in which either the whole or part of the target gene is introduced in either a sense or an antisense orientation (Smith et al., 1988, 1990 a). Expression of the partial sense or antisense effect genes leads to inhibition of the target gene. This allows the precise targeted modification of single or multiple effect genes. This approach has been used to improve textural characteristics of tomatoes by inhibiting enzymes involved in cell-wall metabolism.

The demand for high-consistency tomato products has risen markedly recently, and particularly for strained tomato with a high flavour. Consistency can be improved by using technological processes which minimize pectin break-down by enzymes (polygalacturonase and pectinmethylesterase) on tomato cultivars with high pectin and cellulose contents.

Download Adobe Acrobat Reader (free software to read PDF files)