Pasteurization is a process by which foods are heated to a specific temperature for a specific amount of time to kill (or deactivate) a target number of potentially harmful bacteria. Many different products sold in the supermarket may be pasteurized, including milk, fruit juices, almonds, cider, and beer.
The United States Food and Drug Administration (FDA), through its Center for Food Safety and Applied Nutrition (CFSAN), sets detailed guidelines for the pasteurization of fruit juices. For example, for apple juices with a pH level of 4.0 or lower, the FDA recommends heating processes that "achieve a 5-log reduction for oocysts of Cryptosporidium parvum." These heating processes vary in length of time from 0.3 to 6.0 seconds, with heating temperatures between 160-180°F. Many potentially problematic bacteria, including Salmonella, enter into the FDA's recommendations for pasteurization of fruit juice. For full details on the FDA recommendations, you can visit the CFSAN website at: http://www.cfsan.fda.gov/~dms/juicgu10.html#v.
Pasteurization can reduce some of the nutrients found in juice. I've seen studies showing loss of vitamin C and certain phytonutrients (especially phenols) due to pasteurization, although this impact can sometimes be minimal compared to the amount of pulp lost through juicing.
It is important, of course, for us to put these pasteurization issues into the bigger perspective of whole, natural foods and health. Our ideal step when it comes to fruit is to skip juicing altogether and stick with whole, natural fruits that haven't been processed in any way. As a next best step, we could purchase whole, organic fruits like oranges and make fresh, homemade orange juice just minutes before we drink it. That practice would eliminate the need for pasteurization altogether.
Yet, in addition to my ideals, I am also realistic and know that there are some times when whole, natural fruit or fresh squeezed juice is not an option. Does that mean I would then avoid juice completely? Not necessarily. If there was a need for juice in the diet and pasteurized juice was the only option then I would definitely choose to drink it! That pasteurized juice would still contain important nutrients, and it would be a far better choice than a soda (regular or diet), or even a juice drink.
Look for juice that says "100% juice" on the label so that you won't purchase a juice drink that consists mainly of water and added sweeteners with a minimal amount of fruit juice. . As always, I also recommend that you look for certified organic juices.