 If the banana has temporal parts, this explains how it can change: an earlier temporal part of the banana is unripe, while a later temporal part of the banana is overripe. More grandly: an earlier temporal part has the property being-unripe, while a later temporal part has the property being-ripe. There’s no mystery here, any more than there is mystery in your being both hot and cold by having a hot head and cold feet: we’re all familiar with the fact that different parts of the same object can have different properties.