Pasteurization was developed by French scientist Louis Pasteur about 150 years ago. The process involves heating liquids such as milk and fruit juices to high temperatures in efforts to kill bacteria and other potentially harmful germs. Pasteurization increases “shelf-life” and makes beverages safer to drink, but it reduces some of the heat-sensitive nutrients in fruit juice.
Dairy products, alcoholic beverages and fruit juices are commonly pasteurized. In fact, it’s very difficult to find fruit juice in a mainstream grocery store that hasn’t been pasteurized because it wouldn't remain unspoiled by harmful bacteria. The pasteurization process typically involves heating beverages up to 180 degrees Fahrenheit in order to kill bacteria, although many fungi and parasites are also destroyed by the heat. Flash pasteurization uses higher temperatures and only requires about 10 seconds or less to complete, whereas traditional pasteurization requires up to 30 minutes. Before pasteurizing the juice, the vast majority of inorganic fruit is irradiated with high-frequency gamma rays in order to kill insect larvae, parasites and other pathogens. This method destroys more nutrients than pasteurization.
Vitamin C is needed to make and repair collagen, which is the elastic-like protein found in skin and connective tissues and is important for immune function. Unfortunately, vitamin C is very sensitive to heat and oxidation. Consequently, a significant amount of vitamin C is destroyed by pasteurization, although some juice manufacturers may add more to their products after the pasteurization process to compensate for the loss. Perhaps more importantly, vitamin C deteriorates quickly when exposed to oxygen, so there may not be much viable vitamin C left for pasteurization to destroy by the time the juice gets to that stage. This is why some “before and after” pasteurization studies examining vitamin content may be misleading or confusing.
Antioxidants and Enzymes
Antioxidants in fruits and veggies, especially compounds called phenols, are also very sensitive to heat and oxidation. As such, a significant amount of antioxidants are destroyed by commercial production of juice and the pasteurization process. Antioxidants destroy free radicals, which are chemical by-products that damage and age tissues such as arteries. Fruits, especially pineapple and papaya, contain enzymes that help break down protein and other components of food. Enzymes such as those are also destroyed by heat.
Many pasteurized products are also irradiated, which is capable of destroying other kinds of nutrients because the gamma rays deeply penetrate food and alter the molecular structure. For example, irradiation can destroy vitamins A, B-12, D and E. Irradiation also alters the natural life cycle of plants, which delays ripening and prevents sprouting.
Pasteurization is helpful for making packaged fruit juice safer to drink, but freshly squeezed juice doesn’t pose a health concern in terms of contamination because vitamin C, citric acid and other compounds in fruit and veggies have antimicrobial properties. Concern arises when those protective nutrients break-down due to oxidation, which allows bacteria and other microorganisms to grow and feed on the fructose and other sugars in the juice. Consequently, to get the most nutritious juice that’s safe to drink, squeeze your own at home and immediately drink it.
- Public Health Nutrition: From Principles to Practice; Mark Lawrence and Tony Worsley
- Contemporary Nutrition: Functional Approach; Gordon M. Wardlaw et al.
- Textbook of Nutritional Medicine; Melvyn Werbach and Jeffery Moss
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.