We studied the softening process of fruits occurring during postharvest ripening of `Okubo´ peaches and `Fuji´ and `Jonathan´ apples, and carried out rehardening and preheating in order to increase their firmness, crispness, and rigidity.
The results obtained are as follows:
1. Total pectin decreased slightly, but water-soluble pectin increased greatly during postharvest ripening in `Okubo´ peaches. Polygalacturonase activity increased dramatically during fruit softening.
2. Peaches softened at room temperature and then transferred to 5℃ cold storage tended to increase in firmness, crispness, and rigidity.
3. Weight loss was significant during ripening in peaches. Total soluble solids increased but acidity decreased. The 6-day rigening peaches were most favorable in quality.
4. It was possible to observe through microscope the cell wall disruption and cell separation occurring during ripening in `Okubo´ peaches.
5. Total pectin hardly changed, but water soluble pectin increased initially and decreased slowly at the late stage of ripening in `Fuji´ and `Jonathan´ apples.
6. The preheating treatment after harvest never resulted in significantly firmer apples. However, under the same conditions, `Jonathan´ was more effective than `Fuji´ and `Jonathan´ exposed to 38℃ for 6 days was most effective in preheating treatment.
7. Apples stored at low temperature and then returned to room temperature showed dramatic increase in polyphenol oxidase activity.
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