1. Unit Food Science

2. Problem Area Handling and Storing Plant Products

3. Lesson Oxidative Rancidity

4. Student Learning Objectives 1. Explain why food packaging is a critical component for the food industry. 2. Explain what rancidity is and why rancidity is a problem to the food industry and consumers. 3. Explain the presence of off-flavors in food products caused by oxidative rancidity. 4. Explain various practices that limit or stop oxidative rancidity in foods.

5. Terms Antioxidants Fatty acids Glycerol Hydrolytic rancidity Oxidation Oxidative rancidity Rancidity Saturated fatty acid Unsaturated (polyunsaturated) fatty acids

6. Why is food packaging a critical component for the food industry? Food packaging is critical to food preservation. The purpose is to protect foods from light, microbial contamination, chemical changes, and physical damage. A. Food packaging can be made from a variety of different materials.  1. Rigid and flexible metals can be made into cans, drums, and aluminum foil.  2. Flexible plastics can be turned into a wide variety of containers.  3. Paper, cardboard, and other wood products can be turned into boxes and bags.  4. Containers made from laminates or multiple layers can be created from any of the above sources.

7. B. Packaging machinery and equipment must also be very unique and precise. Equipment must be careful to not contaminate, crush, or otherwise harm food products. C. Food packages must be strong enough to withstand high heat and cold, sterilization, and for highly convenient foods final cooking. D. Food packages must meet stringent guidelines for flexibility, permeability, burst strength, stretch and other qualities. E. Characteristics of good packaging materials include non-toxic, odorless, flexibility, pliable, puncture resistant, good tensile strength at varying temperatures, permeability, low transmission of vapor, easy identification, grease proof, stain proof, good sealing, and easy stripping for the consumer.

9. What is rancidity and why is it a problem? Rancidity is the condition reached in certain foods as the lipid material (fat) undergoes oxidation reactions producing aldehydes, hydroxyl acids, keta acids, and other compounds which are responsible for the odor and off-flavor producing stale foods. An oxygen ion is replaced with a hydrogen ion in the fatty acid. A. Foods that are high in lipids and might become rancid include potato chips, peanut butter, crackers, and others. B. Light, oxygen, trace elements such as iron and zinc, salt, water, bacteria, and molds are factors that speed up the oxidation process.

11. What causes the off-flavors and odors in foods caused by oxidative rancidity? There are two types of rancidity. A. Hydrolytic Rancidity is caused by a breakdown of the fat into glycerol and fatty acid.  1. Fatty acids are organic compounds containing carbon, hydrogen, and oxygen that combine with glycerol to make a lipid.  2. Glycerol is the storage form of fat in animals.

12. B. Oxidative Rancidity results from oxidation of unsaturated and polyunsaturated fatty acids producing undesirable flavors and odors.  1. Oxidation is when a chemical reaction occurs forming oxides by reacting with oxygen in the air.  2. Saturated fatty acids are fatty acid molecules containing no double bonds between carbon atoms—the molecule is “saturated” with hydrogen atoms. Saturated fatty acids are the “bad cholesterol.”  3. Unsaturated (polyunsaturated) fatty acids are fatty acid molecules containing double bonds between carbon atoms—plant oils are unsaturated. These are considered the “good fats.” Unsaturated fats are more susceptible to oxidative rancidity than saturated fatty acids.

14. What practices are used for controlling oxidative rancidity? A. Adding antioxidants—Antioxidants are substances that are added to some foods to slow down oxidative deterioration.  1. BHA—butylated hydroxyanisole  2. BHT—butylated hydroxytoluane B. Package food protected from light because light accelerates oxidation. C. Vacuum packaging to keep oxygen out because oxygen accelerates oxidation. However, this process is too costly for most potato chip manufacturers.

15. D. Adding nitrogen to the bag to replace the oxygen. E. Speed up distribution to shorten the time from processing to consumption. F. Shelf dating products allows for consumers to know when to use food products. Factors that affect the storage life of a perishable food include:  1. length of storage  2. temperature  3. relative humidity  4. light G. Vitamin E and Vitamin C also slow oxidative rancidity.

17. Review/Summary Why is food packaging a critical component for the food industry? What is rancidity and why is it a problem? What causes the off-flavors and odors in foods caused by oxidative rancidity? What practices are used for controlling oxidative rancidity?