Gather up a variety of fruit juices that have varying pH levels. Like most tart or sour fruits, lemons and limes have relatively low pH levels of less than 3.0, while sweeter fruits, such as white grape, apple and orange juice, all have pH levels in excess of 3.0. After soaking a slice of apple in each of the fruit juices, place them on a paper towel or small plate and observe them to see which fruit juices and pH levels had the best anti-oxidizing effect. Lemon and lime juice should do the best job overall of preserving the fruit and preventing it from turning brown due to their low pH levels. Try the same experiment again using lemon juice, citric acid, sugar syrup and ascorbic acid.
Run an experiment to see how moisture impacts apple preservation. Peel two apples and cut them into thin slices. Arrange the slices of one apple on a baking sheet, cover with a layer of cheesecloth and place in a cool area. Place the slices from the other apple into a food dehydrator or on a baking rack in an oven preheated to 150 degrees Fahrenheit. Check the apples periodically over the next 20 to 24 hours and record your results. The apples in the warm oven or dehydrator will have lost most of their moisture content and will look very different from the apples slices left alone.
Since it is oxygen that reacts with an apple’s enzymes to cause it to brown, run a simple test to see whether submerging a peeled apple in water stops the process. After peeling three apples, place one in an airtight container filled with water, making sure the apple is submerged, place another on a dish in the open air away from moisture and the third on a rack set over a small bit of water in an airtight container. Check on the apples at periodic intervals and record your findings.
Light is usually associated with warmth, and most foods will develop bacteria and spoil when exposed to heat for a long period of time. Use a temperature-controlled environment to see whether light alone plays a part in the spoilage of apples. Place peeled apple slices in complete darkness, full light, indirect light, incandescent light and fluorescent light and observe them for several hours to see which apple slices begin to brown first.