Pure butter is made with milk fats. Margarine, however, is created with vegetable fats. Because of the cost difference, margarine is sometimes added to butter. A simple test can identify if butter is contaminated with vegetable fats. Add a small amount of hydrochloric acid to an equal amount of butter melted in a test tube. Then add a pinch of salt and thoroughly mix. After about a minute, if a ruddy red coloring appears in the lower part of the test tube, that is an indication that vegetable butter is present.
Food adulteration occurs when foreign agents contaminate food. Such contamination could happen in several ways, including manufacturers putting in additives or the food coming into contact with bacteria or viruses. Regardless of cause, adulterated food can be harmful or even deadly to consumers. Because of this, designing chemistry projects for students to test food for adulteration is a great way to raise awareness of the types of contamination that may be present in the food they eat.
Bacteria in Milk
Bacteria can find their way into dairy products from a variety of sources, and such bacteria can be dangerous. To test for bacteria contamination, fill a test tube with a mixture of 0.5 grams bromothymol blue and 1 liter of distilled water. Bromothymol blue is a pH indicator that changes color in the presence of carbon dioxide. Add a small amount of a dairy product such as milk, yogurt or butter to the test tube. Stopper the test tube and allow it to stand overnight. If bacteria are present, the blue color will shift toward green and yellow as the bacteria breathe and release carbon dioxide into the tube.
The Purity of Honey
While honey is naturally sweet, some manufacturers may add sugar or cane syrup to boost the flavor and lower production costs. A simple way to test the purity of honey is to add 1 gram of starch (such as potato starch) and an equal amount of iodine solution to a honey and water mixture. Once the mixture is heated, a change in coloration, especially to a shade of blue, indicates the presence of a foreign substance such as sugar. Pure honey will not undergo a color change.
Sugar can also contain adulterated particulates such as chalk power that boost the weight of the product, allowing manufacturers to sell more product at a lower quality. To test for such adulterations, add sugar and water to a test tube and stir. Sugar should dissolve completely, so the presence of particulates in the water would indicate some sort of contamination. To check for chalk powder in particular, add a drop of hydrochloric acid to sugar. If the sugar effervesces (i.e. bubbles or hisses), that indicates there is chalk powder present in the sample.
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