Overripeness (OR) is a natural and inevitable consequence of the senescence which follows the growth and maturation phases that occur in all fruit. It is a general excessive softening of flesh tissue which occurs in the whole mesocarp. In extreme cases tissue breakdown can develop. Nectarines with OR are excessively soft to the touch and the disorder can even manifest as a translucent breakdown of the flesh tissue below the skin in severe cases.
Overripeness can occur due to harvesting over-mature fruit, exceeding the recommended storage period or using the incorrect cold storage temperatures. It is important to note that a small percentage overripe fruit at harvest and packing can lead to a consignment being downgraded as a whole for overripeness. Soft or overripe fruit should therefore not be packed. Typically fruit with OR are very soft to the touch but still look good. The flesh tissue has a translucent appearance and is soft and watery, unlike woolliness or pulpiness, where the affected flesh tissue tends to be dry. The wateriness of overripe flesh tissue is ascribed to cell membranes loosing integrity due to senescence. This allows cell fluids to leak from the inside of the cells into the cell wall area after pectins located in the cell walls have been metabolised to such an extent that they are water soluble, and hence, cannot form gel complexes.
Causes and remedies
Because OR is a natural consequence of the senescence phase that follows maturation, levels will increase exponentially the longer the cold storage period. Nectarines should be stored at -0.5 °C, as higher temperatures may lead to a higher incidence. Fruit should be cooled as soon as possible after packing and/or pre-conditioning, using forced-air cooling to reaching the target temperature of -0.5 °C within 24 hours.
Many complaints about overripeness in cartons of fruit in the market place are the consequence of mixed maturities at harvest. Soft fruit or over-mature fruit should therefore not be packed. With cultivars which are to be pre-conditioned, it is especially important not to pack fruit softer than the norm, since such fruit will become overripe during the pre-conditioning process.
Heat waves in the week preceding harvest can lead to overripeness. Similarly, rain during the same period can cause soft watery fruit. If conditions such as these occur, it is often best to delay harvest by 24 hours after the heat wave of rain event. In this instance it is best to harvest in the upper range of flesh firmness.