Ingredient focus... onions

Healing properties abound - nutritionist Jo Lewin divulges the nutritional benefits, medicinal properties and teary secrets of the humble onion.

Research

Although not nearly as valued a medicinal agent as garlic, onion has been used almost as widely. Onions have been used in folk medicine for the relief of coughs, colds and catarrh, especially asthma, but more recently some of their curative properties have been attributed to a compound called allyl propyl disulphide, which is thought to have a similar effect to insulin in balancing blood sugar levels. This does not mean that the onion can be used as a substitute for insulin therapy; but it may be of help to those who suffer from hypoglycaemia. If you suffer from hypoglycaemia consult your doctor if you have any nutritional queries.

Types of onions

Onions differ in the size, colour and taste. Spring onions are grown in warmer climates and have a milder, sweeter taste. Storage onions are grown in colder weather climates and generally have a more pungent flavour and are usually named by their colour: white, yellow or red. Smaller onions come in many types, such as chives, leeks and shallots.

How to select and store

Globe onions should be clean and hard and have dry, smooth skins. Avoid onions in which the seen stem has developed. Also avoid those that show signs of decay. Onions should be stored at room temperature, away from bright light and in a well ventilated area. Those that are more pungent in flavour such as yellow onions, will keep longer than those with a sweeter tastes such as white onions, since the compounds that produce the sharp taste are natural preservatives as well. All onions should be stored away from potatoes, as they will absorb their moisture and ethylene gas, causing potatoes to spoil more easily. Do not store cooked onions in a metal bowl or storage container as this will cause them to discolour. Freezing chopped onions will cause them to lose much of their flavour.

...Cry me a river: the compound allyl sulphate which is produced when an onion's ruptured cells are exposed to air is responsible for producing tears. To reduce the production of this compound, chill the onions for half an hour or so before cutting to reduce the activity of the enzyme.