Concetti Chiave
- Complex sugars like lactose, maltose, and sucrose are combinations of two simple sugars and can be broken down by heating with dilute acids.
- The iodine test can identify starch in foods like potatoes by turning a blue-black color when iodine solution is applied.
- Vitamins A and D are fat-soluble, resistant to ordinary cooking, but can be destroyed if the fat containing them becomes rancid.
- Vitamin B is water-soluble; it can be lost through over-cooking and should not be cooked with bicarbonate of soda.
- Vitamin C is also water-soluble, easily destroyed by heat, and best preserved by quick cooking methods or consuming raw.
Complex Sugars and Vitamins
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.
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.
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
- ¿Cómo se puede identificar la presencia de azúcares complejos en una muestra?
- ¿Qué indica un cambio de color a azul-negro en la prueba de yodo?
- ¿Cuáles son las características de las vitaminas solubles en agua y cómo deben cocinarse los alimentos que las contienen?
Para identificar azúcares complejos, primero se hierve la muestra con ácido clorhídrico diluido para convertirlos en azúcares simples, que luego se pueden probar con soluciones de Fehling o Benedict.
Un cambio de color a azul-negro en la prueba de yodo indica la presencia de almidón en la muestra, como en papas, arroz o maíz.
Las vitaminas solubles en agua, como las vitaminas B y C, se disuelven en agua y pueden perderse con el calor y la exposición al aire. Los alimentos que las contienen deben cocinarse rápidamente y con poca agua para minimizar la pérdida de vitaminas.
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