Nutrition labels on items in the produce section tend to be short, if not absent altogether. While cereals, soups and sauces come with long lists of ingredients on their packaging, an apple doesn’t need an ingredient list for consumers to know what they’re buying (although it arrived at the grocery store in a labeled package), and the ingredients for bagged salad are only as varied as the different lettuces in the bag. However, more often than not, other substances are at some point applied to the fruits and vegetables available on store shelves in order to kill pathogens or preserve freshness. But unless these substances change the character of the food or are still present in significant amounts by the time they reach the consumer, they are considered a “processing aid,” and do not have to be listed as an ingredient by law. According to the U.S. Food and Drug Administration, processing aids are substances that are added to a food during processing but are either “removed in some manner from the food before it is packaged in its finished form” or “converted into constituents normally present in the food,” or are “present in the finished food at insignificant levels and do not have any technical or functional effect in that food.” For more information about how processing aids are classified, see Food Safety News’ article Processing Aids: What’s Not on the Label, and Why?  What processing aids were used on the produce I’m buying?  Processing aids used on produce are wide-ranging, from chlorine washes to ozone to organic acids to oils derived from plants such as cinnamon or pine trees. “It’s not always across the board for all commodities and they don’t always use [one processing aid] consistently even throughout the season,” says Trevor Suslow, extension research specialist at the University of California Davis. The challenge for a processor is to find the substance that safely delivers the desired effect (pathogen reduction or freshness preservation) without changing the quality or taste of the food. Items marketed as ready-to-eat, such as bagged lettuce or sliced apples, have almost certainly been treated with at least one processing aid, says Suslow. Indeed FDA recommends the use of antimicrobial agents in its guidance for industry on minimizing microbial hazards for fresh-cut fruits and vegetables. “An initial wash treatment may be used to remove the bulk of field soil from produce followed by an additional wash or washes containing an antimicrobial chemical,” writes the agency. One such ready-to-eat product, bagged lettuce, usually goes through two and often three washing phases, says Suslow. The first wash water commonly contains chlorine or chlorine dioxide, while the second might include an antimicrobial agent such as peracetic acid or acidified sodium chlorite – a combination of sodium chlorite and citric acid. Finding the right balance has been a process for the leafy greens industry, says Suslow, as too much chlorine can leave a lingering odor or flavor on greens, and too little won’t be effective at killing pathogens. “As that industry has grown and matured and gotten some strong negative feedback earlier on about chlorine residual taste or smell, which some of the product certainly had, they’ve really worked at minimizing any carry over,” Suslow explains. Peracetic acid is also applied by apple processors, who may use it on apples in a dunk tank or as a spray. A 2007 study from Washington State University found that peracetic acid could also be used on cherries without changing the quality of the fruit when used at low and medium concentrations. The leading method of cherry sanitization is also a chlorine wash, according to the study. Chlorine washes are common across the produce industry, says Suslow. Table grapes are another example of a type of produce often treated with chlorine. “It can vary, but at least the operations that I’ve had the opportunity to visit, it’s pretty much the same,” he says. “They tend to be rinsed in chlorinated water or ozone and then they take the individual grapes off the stem after that.” Stone fruits, such as peaches and nectarines, which are in season right now, often benefit from a chlorine wash as well, says Suslow. FDA has set specified concentrations for processing aids used in washes so that they are present at safe levels. For example, the concentration of sodium chlorite in acid solutions used on raw agricultural commodities and processed fruits and vegetables must remain between 500 and 1,200 parts per million. Other processing aids may be used to keep produce from spoiling. For example, grapes are often packed with pads containing sulfur dioxide to prevent decaying and the growth of mold. On the flip side, processing aids can also be applied to induce ripening. Ethylene gas, for example, is often applied to bananas to speed up the ripening process before they are distributed to retailers, since bananas are commonly harvested in an unripened state. Processing aids for produce: looking forward One sector that’s recently been looking at different processing aid options is the cantaloupe industry. After two deadly foodborne illness outbreaks linked to these melons – a Listeria outbreak that killed 33 people in 2011 and a Salmonella outbreak that sickened 261 people and killed 3 in 2012 – shook consumer confidence and hurt the industry, processors have been looking for a way to ensure consumers of the safety of their product. Processing aids are among the solutions that are being closely examined by the cantaloupe industry, along with brushing, pasteurization and other sanitizing techniques, according to Suslow. An ongoing research project at the Center for Produce Safety is looking at the effectiveness of essential oils — such as those derived from cinnamon bark and pine needles — as antimicrobial agents. “We’re getting promising results,” says Suslow of this research, “and we still have a ways to go.” The trick with these oils, he notes, is to make sure they don’t affect the flavor of the produce to which they’re applied. Another benefit of using essential oils is that they are also organic, a feature that appeals to a growing number of consumers. Will such oils become common as processing aids in the produce industry? That remains to be seen. Suslow says cost is a primary concern, and right now chlorine remains one of the cheapest sanitizing options for produce. Other organic processing aids include lactic acid as an antimicrobial or ascorbic acid (derived from vitamin C) as an anti-browning agent. For an in-depth explanation of organic versus non-organic processing aids, see Food Safety News’ article How Does the Organic Industry Regulate Processing Aids? Another processing aid gaining popularity in the produce industry is electrolyzed oxidized water, which can be generated on-site and is sodium-free. Fresh berries: another approach  Of course not all produce items have been treated with processing aids. Such items may be fragile or susceptible to taste alteration, or companies might have found that other food safety precautions adequately minimize pathogens on their products. Kyle Register, a representative for Driscoll’s, which sells fresh berries, says each berry is handled only once, and goes straight from the farm where it’s picked into a clamshell and then to the grocery store. No processing aids are used on these items. Instead, the safety of the berries is controlled through stringent adherence to the company’s Global Food Safety Program, which is modeled on FDA’s good agricultural practices (GAPs) standards and verified by independent audits. This fruit packaged without a processing aid illustrates what Suslow says is the main take-home point when it comes to processing aids for fruits and vegetables: one size does not fit all. In fact, there’s a different size for pretty much every processor, and even the same processor is likely to be exploring new methods. “There are a variety of different processes and it’s hard to track because they often change from visit to visit,” says Suslow.