Looks good enough to eat

UNDERSTANDING YOUR FOOD<br /> the ultimate educational resource<br /> TEACHER NOTES<br /> <br /> teachers’ notes C1.1<br /> C1. “It looks good enough to eat!”<br /> Pupils investigate whether the colours of a variety of foods and<br /> colourings are affected by the addition of acids and alkalis.<br /> Additional hints<br /> In addition to the foods suggested pupils could also try rosehips, black<br /> and green grapes, blackberries, blueberries, peppers<br /> (red/green/yellow/orange), turmeric<br /> (E100 curcumin).<br /> It is not critical to measure exactly the masses or<br /> volumes. The time for which you leave the mixtures is<br /> also not critical.<br /> Answers to questions on pupil activity sheet C1:<br /> (The optional results sheet (third C1 sheet) can be photocopied for pupils<br /> to use.) The answers below assume that the foods mentioned in the<br /> requirements are used. You will need to alter the questions on sheet C1 if<br /> pupils use other samples.<br /> 1. beetroot and red cabbage only<br /> 2. beetroot, blue colouring, red cabbage, pink colouring<br /> 3. carrot, onion, probably green cabbage, onion skin<br /> 4. In alkali the green cabbage and onion become very brightly coloured.<br /> Bicarbonate of soda (sodium hydrogencarbonate) is an alkali. In the<br /> past, it was added during the cooking of green vegetables to make<br /> them look a bright colour. However, it destroys Vitamin C (present in<br /> the food) so its use is no longer recommended.<br /> 5. Orange squash is normally packed in transparent containers. The light<br /> might make an orange squash containing carotene fade whilst it was on<br /> the shelf or at home. This would probably be unacceptable to the<br /> consumer.<br /> 6. a. There would probably be no objections from the public about health<br /> safety; the marketing people would probably like it because they could<br /> make a big issue on the packet saying something like ‘contains no<br /> artificial colours’; the company itself may think that using natural<br /> colours is preferable to artificial colours.<br /> b. If the food that the colour is to be used in is acidic or alkaline the<br /> colour may change to an unsuitable colour (whatever ‘unsuitable’ means<br /> in this case!); if the food changes in acidity or alkalinity before being<br /> consumed it may change colour; many of these natural colours seem to<br /> fade in the light - not suitable for a product in a clear container standing<br /> on a shelf for, maybe, weeks; some of these natural colours are<br /> expensive; adding other acid or alkali foods to them at home may<br /> change their colour.<br /> 7. This allows pupils to express an opinion. They may suggest to use<br /> names rather than E-numbers because E-numbers do not seem to be<br /> popular with the public and a product may be rejected merely because<br /> it contains them, regardless of the nutritional quality, or other qualities,<br /> of the product.<br /> They may repeat the marketing views.<br /> KS3<br /> science and food technology<br /> Timing - 30 - 40 minutes<br /> Two pupil activity sheets C1 (plus<br /> optional results sheet) accompany<br /> this activity.<br /> Requirements<br /> • balance accurate to 1 g<br /> • knives or other appropriate<br /> cutting equipment<br /> • white tiles or similar as a<br /> cutting surface<br /> • petri dishes or watch glasses<br /> (3 containers are needed for<br /> each sample to be tested)<br /> • distilled water<br /> • any bench acid such as 2M<br /> hydrochloric acid, HCl or 2M<br /> nitric acid, HNO<br /> 3<br /> • alkali such as 2M sodium<br /> hydroxide, NaOH<br /> • teat pipette (those which have<br /> approximate volumes would be<br /> useful)<br /> • samples of food (ca. 10 g) and<br /> food colourings [the following<br /> work very well: fresh beetroot,<br /> red cabbage, green cabbage,<br /> carrot, onion, - the brown<br /> outside onion skin (only 5g)]<br /> • food colourings (the ones trialled<br /> were pink (E127), yellow<br /> (mixture of E102 and E110),<br /> orange (E110) and blue (E123)<br /> • pieces of white paper on<br /> which to stand the dishes<br /> • safety goggles<br /> <br /> teachers’ notes C1.2<br /> Question 7 creates an opportunity for pupils to carry out some research<br /> into consumers’ perceptions of E-numbers and chemical names.<br /> Pupils may like to devise some sort of questionnaire where lists of food<br /> ingredients are shown to consumers and the ‘acceptance’ or otherwise<br /> of E-numbers or chemical names is tested. For example, the same<br /> product could be shown with E-numbers only in one part of the test and<br /> with chemical names only in a different part, without the interviewee’s<br /> knowledge. Is one more ‘acceptable’ to consumers than the other?<br /> For example, the following lists are of thesameproduct (which is an<br /> orange squash; both lists are legal):<br /> water, glucose syrup, oranges,<br /> E330, flavourings, sweeteners<br /> (E951, E954), preservatives (E211,<br /> E223), stabilisers<br /> (E466, E414), antioxidant<br /> (E300), colours (E160(a),<br /> E160(e))<br /> water, glucose syrup, oranges,<br /> citric acid, flavourings,<br /> sweeteners<br /> (aspartame, saccharin),<br /> preservatives<br /> (sodium benzoate, sodium<br /> metabisulphite), stabilisers<br /> (sodium carboxymethylcellulose,<br /> gum acacia), colours (beta-<br /> carotene, beta-apo- carotenal)<br /> <br /> pupil activity C1 “IT LOOKS GOOD ENOUGH TO EA T!”<br /> Weare all attracted by food that looks good. Dull, grey food appears extremely<br /> unappetising and is not what we have come to expect. Our world is full of colourand<br /> many of these coloured things are good to eat.<br /> In this investigation you are going to have a look at some coloured substances. You<br /> are going to see if they are affected by addingacidsand alkalisto them. You will be<br /> asked to think about some of the consequences of your observations on the food we<br /> eat.<br /> Read the safety note before you begin.<br /> SAFETY NOTE<br /> BE CAREFUL WITH KNIVES OR BLADES.<br /> DO NOT CUT TOWARDS YOURSELF.<br /> DO NOT EAT OR TASTE ANYTHING IN THIS INVESTIGATION.<br /> ACIDS AND ALKALIS CAN BURN YOU.<br /> WASH OFF ANY SPLASHES STRAIGHT AWAY WITH PLENTY OF WATER.<br /> TELL YOUR TEACHER WHAT HAS HAPPENED.<br /> In each series of tests, the petri dishes should be placed on a piece of white paper<br /> so that differences in colour are easier to see.<br /> Method<br /> 1.Weigh out three samples ofbeetroot. Each sample should be about 10 g.<br /> 2.Chop up each sample and place in a petri dish.<br /> 3.Add about 5 cm<br /> 3<br /> of distilled water to the first sample.<br /> 4.Add the same amount of distilled water to the second sample. Also add about<br /> 1cm<br /> 3<br /> ofacid to this sample.<br /> 5.Add the same amount of distilled water to the third sample followed by 1 cm<br /> 3<br /> of<br /> alkali.<br /> 6.Take 3 more petri dishes.<br /> 7.In each of them placethreedrops ofbluefood colouring. Repeat steps 3 - 5,<br /> adding the water, acid and alkali to the food colouring.<br /> 8.You will be given a variety of other things which you are going to test in thesame<br /> way.<br /> If the substance is another vegetable, treat it in the same way as the beetroot.<br /> If the substance is a liquid, treat it in the same way as the blue food colouring.<br /> 9.Leave all of your samples for about 5 minutes then look at them carefully.<br /> If you tilt each dish you can see if any coloured liquid is present.<br /> Construct a table into which you can put all your observations.<br /> <br /> “IT LOOKS GOOD ENOUGH TO EA T!” pupil activity C1<br /> Questions<br /> 1.Which foods produced a coloured liquid when onlydistilled waterwas added?<br /> 2.Which sampleschanged colour, (from their colourin water), when acid was<br /> added?<br /> 3.Which samplesonlyproduced coloured liquids when alkaliwas added?<br /> 4.Look at the results for the onion and green cabbage in the alkali. Cooks used to<br /> add a pinch of bicarbonate of soda (sodium bicarbonate) to vegetables such as<br /> sprouts and cabbage during cooking. Why do you think they did this? It is now<br /> understood that adding bicarbonate of soda isnota good thing to do. Find out<br /> why.<br /> 5. The yellow/orange colour from the carrots is calledcarotene. It is a colour that<br /> quickly fades in the light. Why might food manufacturers decide that this was an<br /> unsuitable colour to use in orange squashes?<br /> 6. The colourings from the beetroot, carrot, green cabbage and red cabbageare<br /> obviously allnatural substances. All of them can be used as food colouring.<br /> Their names and E - numbers respectively are:<br /> beetroot E162 betanin<br /> carrot E160(a)alpha, beta and gamma carotene<br /> green cabbage E140 chlorophyll<br /> red cabbage E163 anthocyanins<br /> Think of reasons why food manufacturers:<br /> a.mightwantto use these natural colours in food products instead ofusing<br /> artificial colours;<br /> b. might think they are unsuitablefor food use.<br /> 7.Imagine you are designing the label for a food which uses one or more of the<br /> natural colours named in question 6. In the list of ingredients would you advise the<br /> manufacturer to put just the names of the colours, just their E - numbers or both<br /> names and numbers? Why?<br /> Some foods, like table jellies and boiled sweets, are colourless when they are first<br /> made. Manufacturers then add different colours so that these foods ‘look’ flavoured.<br /> <br /> pupil activity C1 “IT LOOKS GOOD ENOUGH TO EA T!”<br /> How natural food colours are affected by acids and alkalis<br /> Substance Colour in water Colour in acid Colour in alkali<br /> beetroot<br /> blue colouring<br /> carrot<br /> onion<br /> red cabbage<br /> green cabbage<br /> onion skin<br /> (brown outside)<br /> orange colouring<br /> yellow colouring<br /> pink colouring<br /> <br /> HOW DO YOU COLOUR A JELLY BABY? pupil activity C2<br /> The manufacturers of jelly babies add colours to these sweets. Different<br /> manufacturers add different colours. Can you tell the flavour and colour of a jelly<br /> baby if youdon’t look atit before you eat it? Try this out!<br /> In this investigation you are going to remove the colours from jelly babies and transfer<br /> the colours to long pieces of wool.<br /> Read the safety note before you begin.<br /> SAFETY NOTE<br /> DO NOT EAT OR TASTE ANY OF THE SUBSTANCES<br /> USED IN THE INVESTIGATION.<br /> BEWARE! YOU WILL BE USING HOT WATER!<br /> YOU WILL BE USING DILUTE ACID. WASH OFF ANY SPLASHES WITH<br /> PLENTY OF WATER. TELL YOUR TEACHER WHAT HAS HAPPENED.<br /> REMEMBER TO WEAR GOGGLES<br /> Method<br /> 1.Place tworedjelly babies in a small beaker. Add 10 cm<br /> 3<br /> of distilled water.<br /> 2.Heat this and stir with a stirring rod until the jelly babies dissolve. This should only<br /> take a couple of minutes.<br /> 3.Add 1 cm<br /> 3<br /> of dilute acid to the beaker and stir.<br /> 4.Add one length (about 50 cm) of pure white wool to the beaker. Cover the<br /> beaker with a watch glass.<br /> 5.Carry on heating the mixture for about three minutes.<br /> 6.Using your stirring rod, remove the wool and place it in an empty beaker.<br /> Wash the wool thoroughly using plenty of distilled water. Allow the wool to dry.<br /> 7.Repeat this method with the jelly babies of the other colours.<br /> Questions<br /> 1.What happened to the water when you dissolved the jelly babies?<br /> 2.What happened to the wool when you put it in the jelly baby solution?<br /> 3.Make a display of your results.