Effects of Food Preservatives on the Freshness of Food materials (page 2)
Design Your Own Experiment
- Drying foods was one of the earliest methods of food preservation. This method is based on the fact that the bacteria, mold, and yeast known to spoil food do not grow and reproduce without water. Find out more about procedures for preserving food by drying. Place dried and fresh food samples in open dishes (beef jerky and strips of fresh beef make good samples). Examine the food samples daily for evidence of spoilage and determine the effectiveness of drying as a method of preserving. Note: Both samples are inedible and should be discarded after the experiment.
- Table salt (sodium chloride) and vinegar (acetic acid) are used as preservatives. Test the effectiveness of these preservatives on inhibiting bacterial growth. Dissolve one chicken bouillon cube in 1 cup (250 ml) of hot water. Divide the solution equally between three clear glasses. Add 1 teaspoon (5 ml) of salt to one glass and 1 teaspoon (5 ml) of vinegar to the second glass. The third glass is the control. Label the glasses accordingly. Place the glasses in a warm place and examine their contents daily. Spoilage due to the presence of bacteria results in a solution that looks cloudy, has an odor, and often contains gas bubbles.
- Does the amount of preservative added change the results? Repeat the experiment two times, first using less salt and vinegar, and then using a larger quantity of the preservatives.
- Many foods are spoiled by the growth of various fungi in the food. Favorable conditions such as moisture and temperature encourage rapid reproduction of fungi. Sugar is used as a preservative for fruits because it aids in removing moisture from the cells of the fruit. Fungi are less likely to grow in the dryer fruit. Demonstrate sugar's ability to dehydrate fruit cells by peeling an apple and cutting it into small pieces. Place the pieces into a jar and add 1/4 cup (62 ml) of granulated sugar and stir. Secure the lid on the jar. After about 24 hours, the apple pieces will be surrounded by a thick solution of the sugar dissolved in water from the fruit's cells. Use diagrams showing the changes in the jar to represent the dehydrating property of sugar. As part of a display, show examples of products that use sugar as a preservative.
Get the Facts
- The U.S. Food and Drug Administration (FDA) regulates the use of food additives. Nitrates and nitrites are used as preservatives for meat; they also give meat a healthy-looking red color. These preservatives are potentially dangerous because they can lead to the production of cancer-causing chemicals in the digestive system. FDA regulations allow foods to contain up to 500 parts per million (ppm) of nitrate and 200 ppm of nitrite. It is considered safe for adults to consume these preservatives at this low level, but foods for babies under one year of age should contain no nitrate or nitrite additives. Find out more about nitrates and nitrites. Could other safer methods of preserving meats be used?
- The food additive sodium benzoate is on the GRAS list. This chemical occurs naturally in many foods, such as prunes and cranberries. It is naturally present and part of the metabolic process in the human body. Find out more about sodium benzoate. What conditions must exist for it to be effective? list foods it is used in. What is considered a harmless level for human consumption?
- The FDA allows preservatives to be added to foods at specific levels. How are these safe levels of consumption determined?
- Five types of microorganisms that cause food to spoil are staphylococci, bacilli, molds, streptococci, and yeasts. These organisms feed on much the same substances as do humans and, when present, can bring about undesirable chemical and physical changes in food. With the right conditions, they can double in number every 20 or 30 minutes. Find out more about these food spoilers and how they can be controlled. You could prepare a data table for display showing diagrams of the five types of microorganisms and listing specific types of food spoilage, such as botulism (one of the most serious types of food poisoning) or simple fermentation by yeast. (See the sample data table in Figure 20.2.)
- Find out more about advancements in preserving foods. Compare home food preservation methods in the past and at present. Some things have changed very little, such as the smoking of meats on an open fire. You could use diagrams to compare old and new techniques.
- In the late-eighteenth century, Napoleon offered 12,000 francs for a new way of preserving food. Nicolas Appert, a Parisian chef, won the money with his heat-preserved foods. Find out how this man without any knowledge of bacteria and its role in food spoilage was able to preserve food.
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