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Dairy food and cheese-making Dairy • Dairy products are foods that are made from milk • Examples: cream, milk, cheese, yoghurt • The molecules in milk includes ALL those required for a growing baby mammal. It is the only food source mammal have until they are weaned off their mother’s milk. How does milk make cheese? • Milk needs to be coagulated, the solids (curds) are then separated from the liquids (whey) • Coagulation is the process of the proteins in milk (casein) becoming tangled into solid masses, called curds. • In cow’s milk approximately 80% of the protein is casein How does milk coagulate? • Milk curdles (coagulates) when the pH becomes acidic or an enzyme is added (eg. rennin) • Milk will coagulate by adding: – An edible acid like lemon juice or vinegar – Lactic acid bacteria or yeast – rennet (from the stomach of mammals that contains the enzyme rennin) pH • What is pH (definition)? • Complete the following table: Acidic Acidic substances foods Neutral Neutral substances foods Basic Basic substances foods Acids added to milk • By adding an acid to milk it changes the acidity of the liquid (the pH). • When the pH gets below about 5, the proteins denature (change shape) and chemically change to form larger molecules that are hydrophobic proteins (solid, masses called curds) Lactic acid bacteria • These are organisms that use the sugar, lactose, in anaerobic respiration • The bacteria produce lactic acid which lowers the pH of the milk, that results in coagulation • The bacteria used are low-pH tolerant species and so can survive where other pathogenic species cannot Rennet contains an enzyme, rennin • Enzymes are special proteins • They are present in the cytoplasm of all cells • They help to speed up the chemical reactions in the cell • There are hundreds of different enzymes but each enzyme speeds up only one kind of reaction • Rennin makes casein hydrophobic, causing it to form solids in the whey Yeast • Yeast is a type of fungus, or mold. • These are organisms that also use sugars in anaerobic respiration but the chemical reaction is different because their anaerobic respiration makes ethanol and carbon dioxide (not lactic acid). • Yeast and other types of fungi are used to add flavor to cheese, such as blue cheese and camembert.