macronutrients Flashcards
Protein
Secondary source of energy Mainly used for growth and repair Any protein not used as this will be stored as fat Protein foods don’t just supply protein Additional calories maybe in foods supplied by carbohydrates or fat
Denaturation in protein
When the physical structure of the protein is altered in an irreversible way. The protein becomes less soluble and more viscous e.g. whisking egg whites Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound
Coagulation in protein
Irreversible Coagulation involves the denaturation of protein: changing from a soluble to an insoluble structure e.g. When eggs are heated, the proteins in the white and yolk coagulate. Egg white proteins coagulate first at about 60oC and the white becomes opaque and forms a gel. The yolk proteins coagulate at 66oC and the yolk thickens As a result, of denaturation, the properties of proteins alter: they become less soluble and more viscous. The unfolded molecules tend to form clumps, as they bond with each other. This results in the setting or hardening of protein foods
Effect of heat on protein
Only globular protein Heat causes the secondary structure of proteins to denature, where the molecule unfolds and changes shape but the sequence of amino acids remains the same. Denaturation breaks the cross linkages which maintain the shape of the molecule. It is usually irreversible. As a result, of denaturation, the properties of proteins alter: they become less soluble and more viscous. The unfolded molecules tend to form clumps, as they bond with each other
Effect of acids/alkalis on
protein
Fibrous proteins are not greatly affected by acid, but globular proteins are. Acid can start to make proteins coagulate (e.g. starter cultures in cheese and yoghurt) It breaks down the tertiary structure of protein, e.g. in meat – the use of acidic marinades (vinegar, lemon juice, wine or even tomato juice). The acid
increases the rate at which collagen is converted to gelatine Acids can be used on meat and fish products to cook the flesh. The flesh does have to be sliced very thinly. Acidic foods can act as a tenderiser on meats to help turn a tough cheap cut of meat into a tenderer and higher quality meat. Typically, we use buttermilk in curries etc. to act as a tenderiser as it is highly acidic – lemon and other citrus juices and rock salt to act as a cure
Effect of mechanical action
on protein
This causes denaturation (which can be reversible), followed by coagulation (irreversible), (when heated/cooked), such as in the whisking of egg white. The protein molecules unfold and form a reinforcing network around the air bubbles, thus stabilising the foam. Food products such as meringues and soufflés are examples of this effect. Mechanical pounding, cutting up meat, mincing helps to break up longer muscle fibres.
Effect of cooking methods
on meat
Animals such as cows, sheep and pigs tend to live a reasonably long period of time before being slaughtered and as a result of their lifestyle, their muscles and connective tissues become developed and stronger (tougher) as they get older. The older the animal, the longer and thicker the muscle fibres. Parts of the animal which are used a lot, such as the legs and neck develop thick, long fibres. The more connective tissue present, the tougher the meat. These cuts of meat tend to cost less because they are less palatable, unless cooked by slow, moist cooking methods. Breaking the fibres down prior to cooking, either by bashing it (mechanical means), marinating it (chemical means) or mincing / dicing it small can help to tenderise the meat. Proteolytic enzymes are used to digest muscle fibres and connective tissue in the food industry, but foods such as figs, pineapple juice, and kiwi fruit can be used at home. Cooking by long, slow, moist cooking methods such as braising, stewing will convert the collagen into gelatine. small, narrow fibres is more tender than meat made up of larger fibres, often developed through activity
Maillard reaction
Some flour products are cooked by dry heat, in form of radiation/convection As this happens proteins and carbohydrates react on surface This results in colour, flavour and odour changes e.g. toast
Monosaccharides
Sugar Glucose, fructose, galactose Quick release Simple carbohydrates C6H12O6
Disaccharides
Sugar Maltose, sucrose, lactose Quick release Simple carbohydrates C12H22O11 formed when two Monosaccharides join together during a condensation reaction (when water is eliminated)
Polysaccharides
Non sugars C6H10O5 Simple – starch, cellulose, glycogen Long chains of 1 type of monosaccharide joined together. Usually insoluble in water Complex – pectin, gums These are long chains of different monosaccharide’s joined together and often with branches Slow release Complex carbohydrates
Glucose
Monosaccharide Found in large amounts of grapes and smaller amounts in carrots and peas Glucose syrup is used in manufacture It’s a reducing sugar There are two forms of glucose alpha and beta only difference in the two is that in alpha glucose, the hydroxyl group (OH), is at the bottom of the structure and in Beta glucose, the OH is at the top
Fructose
Monosaccharide Fructose is one and a half times sweeter than glucose. An equal mixture of fructose and sucrose is called invert sugar – found in honey, made when making jam. The structure of Fructose changes depending on if it is found in its own or whether it is joined with other sugar
Galactose
Monosaccharide This doesn’t occur in foods but it is formed when lactose if broken down during digestion
