Nutrients and their chemical tests
- Nutrients provide energy and molecules for repairing cells and tissues.
- Seven nutrients for a balanced human diet: carbohydrates, proteins, fats, vitamins, minerals, fibre, water.
- Carbohydrates contain carbon, hydrogen and oxygen and include sugar and starches. Glucose = a simple sugar made in photosynthesis and used for respiration. Complex sugars e.g. sucrose, maltose and lactose are made of two simple sugars joined together. Complex carbohydrates like starch are made when many simple sugars are joined together. Glycogen = complex carbohydrate in animals, stored in liver.
- Proteins are made up of carbon, hydrogen and oxygen, and also contain nitrogen. Some have sulphur. They are long-chain molecules made from amino acids. There are around 20 amino acids, and the sequence of amino acids in a chain determines the protein.
- Fats and oils are made from carbon, hydrogen and oxygen. A fat or oil contains one molecule of glycerol with three fatty acids attached to this. They are used for energy storage and thermal insulation.
- Starch test: iodine solution (a yellow/light brown) turns black in the presence of starch.
- Reducing sugars test: Benedict's solution (bright blue) turns red or orange after turning green/yellow first, if there are reducing sugars. A deep orange colour = lots of reducing sugars.
- Protein test: biuret solution (blue) turns a purple colour in the presence of protein.
- Fat test: If a solution of fat in ethanol is added to water a cloudy white emulsion forms.
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Sources of nutrients
- Carbohydrates: rice, potatoes, bread, yams, sugar, honey.
- Proteins: meat, fish, milk and nuts.
- Fats: butter, cheese, fish, nuts.
- Water: in many foods and drinks. It is needed for chemical reactions.
- Fibre: plants. It cannot be digested but adds bulk to food to help the movement of food by peristalsis.
- Vitamins and minerals: Vitamin C - oranges, lemons, citrus fruits. Vitamin D - fish oil, milk, butter. Iron - liver, meat, cocoa, eggs. Calcium - milk, fish, green vegetables.
- Vitamin C is used for tissue repair and resistance to disease. A deficiency may lead to bleeding gums (scurvy).
- Vitamin D strengthens bones and teeth. A deficiency leads to soft bones and rickets.
- Iron helps form haemoglobin in red blood cells. A deficiency causes anaemia.
- Calcium strengthens bones and teeth. A deficiency causes weak and brittle bones, and muscle weakness.
- Microorganisms are used for food production. Bacteria are used to produce yoghurt - they are added to milk and respire anaerobically using lactose. This produces lactic acid so the milk's pH lowers and it coagulates. It is batch cultured.
- Mycoprotein is a high protein material produced by Fusarium, a fungus. It is made by continuous culture where nutrients are continually added and the products continually removed. The hyphae of the fungus are processed - it can be made into a meat substitute that is high in protein but low in fat.
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- Pickled foods contain vinegar (ethanoic/acetic acid) which has a low pH to stop microorganisms growing.
- Additives can colour, preserve and add flavour to food. Some are natural, some are synthetic and they are added during processing.
- Colourings add colour back in that is lost from processing so it is more appetising.
- Preservatives and anti-oxidants stop food from being decomposed by bacteria or being oxidised.
- Flavourings are used to re-create natural flavours using a mixture of compounds - monosodium glutamate enhances natural flavours of food.
- Emulsifiers and stabilisers enable fats and oils to mix with water.
- Food additives have a numbering range which is used internationally. 100-181 = colouring, 200-290 = preservatives, 296-385 = anti-oxidants and acids, 400-495 = emulsifiers and stabilisers. 500-585 = anti-caking agents and mineral salts, 620-640 = flavour enhancers, 900-1520 = others e.g. sweeteners, wax glazes on fruits.
- Tartrazine (102) is a colouring linked to hyperactivity in children and provoking asthma attacks.
- Butylated hydroxyanisole (320) is banned in Japan because of links to cancer.
- Saccharin (954) is a sweetener, banned in the USA after tests on rats. Legislation was passed so no health warning on labels is needed as research has shown it isn't harmful.
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