Tony Gane, of Stratford, asks :-

Many of our fruit and vegetables are picked well before they are naturally ripe, because of export markets or supermarkets here. Sometimes they sit at home for up to two weeks before they soften and colour up. Do these early picked fruit and vegetables contain the vitamins and minerals full-term tree-ripened fruit and full-term ripened vegetables have? Does the early picking compromise our health in other ways? Have tests been done on the vitamin C content and minerals between the two stages of ripening?

Roger Harker, a plant physiologist at The New Zealand Institute for Plant and Food Research Limited, responded.

Many consumers buy fruit on a weekly cycle and depending on the type of fruit they might be able to start eating it straight away or they may need to wait a few days for it to ripen. Sometimes the fruit gets forgotten and ends up being thrown away, or is used in cooking. Each fortnight about 50% of New Zealanders end up wasting some of the fruit that they buy.

Fruit is harvested at a stage of growth when we know that it will be able to ripen off the tree/vine and provide consumers with a good eating experience. For many fruit this stage is the optimum point for accumulation of minerals and nutrients, but before ripening has progressed to the point that deterioration can't be slowed down by refrigeration. Each fruit is alive and the biological processes continue while in refrigeration as well as in our homes: the flesh softens, the starch breaks down into sugars and some of the acids are used in respiration. These are processes that need to take place for the fruit to become palatable.

Generally some of the phytochemicals that are thought to promote human health increase during ripening while others decrease during ripening - and this is the case whether fruit ripens on or off the tree/vine. Not all fruits contain Vitamin C, but for many of those that do, the concentrations that are helpful to human health are maintained during ripening.

Most consumers don't have the opportunity to eat tree-ripened fruit. It cannot be easily stored or distributed to retail stores. Consumption of fruit is important for human health and wellness, and it is important that we provide a continuous supply throughout the year, at reasonable prices and of a quality and taste that encourages consumers to eat more.