Optimal Value

Thiamin leaches out easily into cooking water and is lost readily if cooked in the juices from meat. Like vitamin C, thiamin is unstable under alkaline conditions and so is also easily lost if sodium bicarbonate is added during cooking. Around 5 to 15 per cent of thiamin is lost from eggs if they are boiled, fried or poached.

Riboflavin, which is found in milk, is equally unstable and can be destroyed by light. It is therefore important not to leave bottles out on the doorstep exposed to sunlight for more than an hour, or else large losses can occur.

Meat, which is a good source of the B group vitamins, also loses nutrients when cooked, although different methods will affect the amount lost. Frying or grilling meat will lead to a loss of around 20 per cent, whereas stewing will lead to greater losses - between 20 to 70 per cent, depending on whether the juices are consumed, since most of the nutrients will have seeped into the juice.

B vitamins can also be lost while cooking fish - around 10 to 30 per cent are lost if fish is baked, fried or grilled.

Other vitamins and minerals
Generally, fat-soluble vitamins, such as vitamin A, D and E, are stable regardless of the cooking method used. Minerals are also unaffected by heat but can be lost in the cooking water when boiled or blanched or steamed.

Cooking tips
The best way to preserve all of the above vitamins when cooking meat, fish or eggs is to remember the following basic points:

• Boil or steam vegetables for a minimum length of time in a minimum amount of water.
• Boiling vegetables in the microwave is a useful way to minimise vitamin C losses, since this process heats them up rapidly and uses only a minimum amount of water.
• If not stored for long periods of time, fresh fruit and vegetables are the best sources of all water-soluble vitamins. However, there are large losses of vitamin C and folate in fruit and veggies that have been stored for long periods and are wilted.
• Don't throw away the cooking water, as you'll be throwing vitamins and minerals down the drain. Keep them to use for gravy.
• Keep the meat juices and use it as gravy as they also retain a large amount of vitamins and minerals. Remember to skim the fat off first.