Ripening Stages of Cranberry Fruit Have a Dramatic Influence on Its Postharvest Shelflife: Physiological and Morphological Explanation

Cranberries ripen in late fall. The fruit develops color in the outer two cell layers in response to low temperatures and incident light. Berries at the top of the canopy generally develop full red color, whereas fruits lower in the canopy (especially under dense canopies) can remain white even at harvest time. This is especially true for Wisconsin-grown cranberries. Wet-harvested cranberries are stored for 1 to 2 months and sold at Thanksgiving and Christmas time. We investigated if the storage quality of fruit is dependent on ripening state. Wet-harvested fruits were sorted into four different ripening stages and rated for quality after 4 and 7 weeks of storage. In addition, fruit CO2 and ethylene production, as well as anthocyanin content, were measured after 4 weeks of storage. The amount of rotten fruit among red, light red, blush, and white were 12%, 14%, 23%, 38% respectively. Thus, white fruits had three times greater incidence of rot than the red fruits. Although the ethylene production by various categories of fruit was nearly same, white fruits had 70% higher respiration than red fruits. We also found that as the fruit developed color cuticle thickness increased. For example, cuticle thickness averaged 1.6 μm for white fruit and 2.3 μm for red fruit. In addition, the calyx end opening of red fruit was impregnated with more wax than white fruit. Furthermore, a compact cell layer accumulated anthocyanin under the calyx opening in red fruit only. Our studies suggest that white berries have poor shelf-life as compare to red fruit because: i) white fruits have higher respiration rates, ii) thicker cuticle and wax accumulation (especially at the calyx end) on red fruits retard the entry of microorganisms into the fruits during wet harvest.