Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Texture of heat processed fruits

The project concerned the optimization of texture in heat processed fruit by controlling the process (via the optimization of pre-processing treatments), and by the control of fruit ripening prior to processing (via genetic manipulation). The pre-processing treatment for each fruit involved reduction of pressure, time under vacuum, holding time for calcium infusion, temperature of infusion, calcium concentration of the solution, and pH of the solution. Strawberry fruit thus treated exhibited up to a 12-fold increase in firmness after a blanching process compared to its control (untreated blanched). Moreover, after a standard canning process the optimally pre-treated fruit showed a 7-fold increase in firmness. The optimized pre-treatment conditions for tomato fruit resulted in a greater than 2-fold increase in firmness after blanching and a 3-fold increase in firmness after canning relative to 'canned only' fruit. Industrial scale-up of the pre-treatment method using standard processing varieties resulted in canned tomatoes with further improved textural characteristics (a 3- to 4-fold increase in firmness). Sensory evaluation confirmed these effects and showed no negative impact on flavour. Investigations of the microstructure showed a considerable retention of raw fruit cell wall structure in pre-treated canned fruit. The results show that the optimized pre-treatments succeeded in activating the structure-conferring enzymes and reactions, while significantly limiting the texture degrading processes taking place during the heat processing of fruits.

The route of genetic down-regulating of pectin enzymes normally present in tomatoes did not lead to any significant changes in texture after processing. Neither were there any molecular nor microstructural differences between the transgenic raw fruit and their control. These findings highlighted the need for a deeper understanding of the implications of down-regulating pectin enzyme activity in a complex fruit matrix.

Reported by

LEATHERHEAD FOOD RESEARCH ASSOCIATION
RANDALLS ROAD
KT22 7RY LEATHERHEAD
United Kingdom
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