(D) The Chemistry of Cooking and the Oxidation of Food HC CHEMISTRY HC CHEMISTRY NATURES’ CHEMISTRY (D) The Chemistry of Cooking and the Oxidation of Food

(D) The chemistry of cooking and the oxidation of Food HC CHEMISTRY HC CHEMISTRY (D) The chemistry of cooking and the oxidation of Food Kitchen Chemistry After completing this lesson you should be able to : Within proteins, the long-chain molecules may be twisted to form spirals, folded into sheets, or wound around to form other complex shapes. The chains are held in these forms by intermolecular bonding between the side chains of the constituent amino acids. When proteins are heated, during cooking, these intermolecular bonds are broken allowing the proteins to change shape (denature).These changes alter the texture of foods. and acidified dichromate solution can be used to differentiate between an aldehyde and a ketone. Many flavour and aroma molecules are aldehydes. In terms of intermolecular forces, explain the influence of functional groups, including hydroxyl, carbonyl and carboxyl, on solubility, boiling points and volatility. Antioxidants in foods.

Taste “The notion that the tongue is mapped into four areas—sweet, sour, salty and bitter—is wrong.  There are five basic tastes identified so far, and the entire tongue can sense all of these tastes more or less equally. As reported in the journal Nature this month, scientists have identified a protein that detects sour taste on the tongue.  This is a rather important protein, for it enables us and other mammals to recognize spoiled or unripe food.  The finding has been hailed as a minor breakthrough in identifying taste mechanisms, involving years of research with genetically engineered mice.  This may sound straightforward but, remarkably, more is known about vision and hearing, far more complicated senses, than taste.” - Live Science The five tastes are: Sweet Salty Bitter Sour Umami (savoury)

Are you are super taster? Experiment 1 – Phenylthiocarbamide Lick the strip and tell us what you taste. Phenylthiocarbamide PTC – Chemistry World podcast

Experiment 2 – Taste test Blind-folded pupil (or with eyes closed and no peeking) is given a selection of jams to taste. The taster should hold their nose and see if they can detect the flavour of the jam. The taster again is then to determine which flavour of crisp they are eating while another flavour crisp is held under their nose. Molecular basis of flavour The role of volatile molecules in flavour can be illustrated by an experiment where foods are tasted while your nose is blocked. Strawberry jam works well. A blindfolded taster is fed a small amount of strawberry jam with a teaspoon. While holding his/her nose, the taster can detect the sweetness of the jam (which is detected with the tongue) but will be unable to tell the flavour of the jam, which is caused by volatile molecules detected by the nose. On releasing his/her nose, the taster will be able to tell the flavour of the jam. Other foods which can be used in this experiment include apple, parsnip, and even different flavours of crisp. In this variation the taster is given a plain crisp to taste but, without telling them, a flavoured crisp is held under their nose. The taster will report that the crisp they are tasting has the flavour of that held under their nose.

Flavour in Food Experiment 2 – Taste test

The Chemistry of flavour molecules Formative assessment 1 – read and answers questions on pages 3-6 Molecules responsible for flavour in vegetables are normally trapped inside the cell walls. During cooking the cell walls are damaged for two reasons: • Chemical damage occurs as the cell walls, which are made of cellulose, break down. • Physical damage occurs as water inside the cells boils forming steam and the cell walls break open. A major issue in cooking is to retain molecules responsible for flavour in the food – overcooking can result in loss of these molecules. One destination for lost flavour molecules is in the cooking water. This will occur if the flavour molecules are water-soluble. If this is the case, many of the flavour molecules will be lost down the drain when the cooking water is poured away. Referenced article

The Chemistry of flavour molecules

b) Flavour in food- Changes upon heating Learning intention Learn how heating protein-containing foodstuffs leads to a change in food texture as intermolecular forces are broken.

Changes in protein structure on heating Within proteins, the long chain molecules may be twisted to form spirals, folded into sheets, or wound around to form other complex shapes. The chains are held in these forms by intermolecular bonding between the side chains of the constituent amino acids. When proteins are heated, during cooking, these intermolecular bonds are broken allowing the proteins to change shape (denature).These changes alter the texture of foods.

Changes in Food upon heating Experiment 3 – Cooking meat and the Maillard-Hodge reaction of browning Maillard-Hodge reaction

Other types of browning Experiment 4 – Enzymic browning This reaction differs from the Maillard reaction in that proteins and amino acids are not involved. Formative assessment 1 – read and answers questions on pages 9-13 Enzymic browning