Concetti Chiave
- Complex sugars like lactose, maltose, and sucrose are formed by joining two simple sugar molecules and can be broken down into simple sugars through heating with dilute acids.
- The iodine test is used to detect starch; a blue-black color appears when iodine is applied to starch-containing foods like potatoes.
- Vitamins A and D are fat-soluble, resistant to ordinary cooking but destroyed when the fat containing them becomes rancid.
- Vitamin B is water-soluble; cooking with minimal water and avoiding over-cooking preserves its content in food.
- Vitamin C is also water-soluble and sensitive to heat and air; it's best preserved by quick cooking methods or eaten raw in foods like oranges.
Complex sugars and their breakdown
Examples of complex sugars are lactose-milk sugar, maltose-malt sugar, sucrose-cane sugar.
These are formed by the joining up of two simple sugar molecules. When they are heated with dilute acids they are broken down into simple sugars. Therefore, to test for complex sugar, the sugar is first boiled with dilute hydrochloric acid so as to convert it to a simple sugar solution. The resulting simple sugar can then be tested with either Fehling's or Benedict's solution.
Test for Starch ( for example potatoes, rice, maize)
Iodine test:
1. Cut a thin slice of potato.
2. Place it in a clean flat plate or glass slide.
3. Drop 1-2 drops of dilute iodine solution in the cut slice.
Observation:
Blue-black colour is formed. This shows the presence of starch.
What are vitamins A and D?
Vitamins: there are different types of vitamins
Vitamins A and D:
- these are fat soluble vitamins.
- they are not dissolved in water.
- they are not destroyed by ordinary cooking.
- they are destroyed when the fat that contains them goes rancid or rather when it gets spoilt.
Vitamin B:
- this is water-soluble which means it dissolves in water.
- Food sources should be cooked with small quantity of water.
- fast method of cooking should be used. Over-cooking can lead to loss of vitamin.
- food should not be cooked with bicarbonate of soda or local potash.
Vitamin C:
- this is a water-soluble vitamin.
- it is easily destroyed by heat and exposure to air.
- it can be lost by soaking in water.
- they should be cooked in small quantity of water using quick cooking method.
- rich vitamin C foods such as oranges are often eaten raw.
Minerals:
- dry heat has little effect upon minerals in food.
- moist heat may result in the loss of some of the soluble minerals such as sodium, potassium and magnesium salts.
Domande da interrogazione
- How are complex sugars broken down into simple sugars for testing?
- How do vitamins A and D differ from vitamins B and C in terms of solubility and cooking effects?
Complex sugars, like lactose, maltose, and sucrose, are broken down into simple sugars by heating them with dilute acids. This process is necessary before testing with Fehling's or Benedict's solution to confirm the presence of simple sugars.
Vitamins A and D are fat-soluble and not destroyed by ordinary cooking, but they degrade when the fat containing them spoils. In contrast, vitamins B and C are water-soluble, easily lost through over-cooking or exposure to water and air, requiring quick cooking methods to preserve them.
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