WJEC GCSE Food and Nutrition: Revision Guide

87 FRUIT AND VEGETABLES SECTION 3 Science of fruit and vegetables Enzymes, oxygen and naturally occurring moulds and yeasts cause spoilage and decay of fruit and vegetables. Yeasts and moulds feed on the moisture and sugar of fruit and vegetables making them soft, mushy and discoloured. They will then look, smell and taste unpleasant. Apples, pears, parsnips, potatoes, bananas and avocados go brown, grey or black once peeled, sliced or grated. This is due to enzymic browning which is a reaction between the plant cell enzymes and oxygen. To prevent enzymic browning the fruit and vegetables must be treated in some way, for example covered with water/water + lemon juice, blanched or cooked immediately. Fruit and vegetables that contain natural sugars will caramelise when cooked. As the plant cells are heated, the natural sugars turn into caramel, browning the food. Examples are fried onions and bananas. Starchy vegetables, such as potatoes, can thicken a liquid through gelatinisation. When the starch cells in the potato are heated they will soften and absorb some of the surrounding liquid. To thicken a casserole or stew simply place diced potato into the gravy and continue cooking. The potato will absorb some of the liquid, creating a thicker gravy. 7 What reacts with the enzymes to make bananas go brown? 8 How would you prevent peeled potatoes from discolouring? How would you prevent an apple from going brown like this? Why do onions caramelise? Grade boost Make sure that you can explain and give examples of enzymic browning, caramelising and gelatinisation. Why is it important to eat a rainbow of fruit and vegetables?