Growth, ripening and storage of tomato fruits

Publication I.

A non-destructive, automated, fast and portable softness measuring device is described. The non-destructivity of the meter was established.

Factors that might influence the variation in softness-readings, e.g., temperature, relative humidity, the point of compression on the fruit, sampling in the greenhouse, and fruit size were experimentally investigated.

It was concluded that, although all these factors influence the dispersion of the softness readings, the individual tomato fruit by its own qualities causes the greatest dispersion. The developed meter therefore is a useful tool for comparative softness measurements of tomatoes.

Publication II.

A scale is presented for the rating of tomato fruit ripening by visual determination of the skin colour in 8 stages. The stages 2 to 7 closely correspond with changes in reflection of fruit homogenates, softness, specific gravity, Internal ethylene concentration, and respiration.

The ascorbic acid is mainly confined to the pericarp tissue, its content does not change with ripening.

Publication III.

Experiments with tomatoes were carried out to analyse the interaction of fruit growth and fruit:leaf ratio, and of ripening and position of the fruit on the truss.

Different fruit:leaf ratios give different yields. Fruit weight and volume are positively correlated with the leaf area per fruit. Total yield, however, depends mainly on the number of fruits per cluster.

No differences in postharvest quality were found between fruits picked early in the morning and in the afternoon.

A fruit:leaf ratio of 1:3 gives uniform fruits. However, the more leaf area per fruit, the more fruits with greenish coloured locular tissue occur. The seeds in this anomaly coloured tissue are less germinable than those of red-coloured jelly. The ascorbic acid content of fruits with greenish coloured locular tissue is higher than that of normally coloured fruits. The data are consistent with the view that there might be a ripening inhibitor, originating from the leaves and acting also on the physiological condition of the seeds .

For the different positions of fruits in the truss, the morphological and physiological ages did not differ sinificantly. Only in 50-60% of the trusses the fruit nearest. to the main stem was the first to be fertilized and to mature. Weight is positively correlated, ripening, however, negatively correlated with the number of seeds.

Unripe fruits detached from the vine, but kept under the same conditions as those on the vine, have hardly the tendency to ripen more rapidly. Therefore the occurence of a ripening Inhibiting substance from the foliage is not conclusively demonstrated in tomato.

Publication IV.

The optimum picking time for tomatoes is determined from physiological and anatomical data.

A special method of photographing changes in volume of tomatoes on the vine is described. A new technique of printing shows directly the change in volume at different stages of development .

Specific gravity increases in the course of ripening as a result of structural changes in the parenchymous cells of the pericarp tissue, involving a reduction in size of the intercellular space. The increase in specific gravity of fruits on the vine is accompanied by increases in volume and weight, whereas picked tomatoes decrease in size while ripening.

Fruits picked when 50% orange or even riper give the highest yield and best postharvest qualities.

Publication V.

During subsequent years experiments were carried out with various storage conditions of tomatoes, varying in temperature, humidity and controlled atmosphere (C.A.) treatment.

The tomatoes were picked at different colour stages. Fruits harvested at green stages are more susceptible to damage at high humidity and low temperature than the more advanced ones, resulting in a shorter shelf life and more decayed fruits.

C.A. storage was, under the experimental conditions, no improvement of the standard storage at 12.5 - 13 °C in air. However, there are indications that treatment with a fungicide and storage under reduced atmospheric pressure prolong storage life.