High Pressure Processing
Low temperature also is the new emphasis for high pressure processing (HPP), with processors and equipment suppliers employing terms like “cold-pressed processing” to describe the technology.
The cold emphasis is partly a counterpoint to researchers and regulators focused on high pressure and heat to inactivate Clostridium botulinum in low-acid foods. While HPP destroys bacteria and viruses in food, it does not eliminate spore formers such as C. bot.
The effectiveness of HPP and heat in destroying C. bot is well known: In 2009, FDA accepted a petition for commercial use of such a process involving low-acid food (mashed potatoes) from Illinois Institute of Technology, Avure Technologies Inc. and the forerunner of the Institute for Food Safety and Health (IFSH), which is based in Bedford Park, Ill., in a facility that includes an office of FDA’s Center for Food Safety and Applied Nutrition. However, no food companies were interested in producing such a product, and it’s doubtful that HPP’s strengths—better flavor and higher nutritional value than canned foods—would be retained. In fact, conventional HPP might have a protective effect on spores when combined with processing temperatures of 80°C/176°F. The pressure needed for inactivation would be greater than the upper limits of the approximately 350 HPP presses currently in operation worldwide.
Aside from commercial impracticality, such treatment runs counter to the appeal of cold-pressed juices, which are refrigerated and popular in part because of minimal processing. If the cold chain is broken and product is held for an extended period above 50°F, a C. bot culture can develop—as was the case in 2006 with carrot juice produced by Bolthouse Farms. Several botulism cases tied to the carrot juice were reported.
Consequently, FDA inspectors have demanded that HPP processors either acidify juices above 4.6 pH or prove that a 5 log reduction in C. bot occurs in their process. Addition of citric acid can lower pH, but it isn’t an option with coconut water, which has a mild taste that would be masked by another flavor. FDA fired off a warning letter to Harmless Harvest, a leading coconut water brand, in November, demanding that it validate a 5 log reduction in C. bot. The firm subsequently abandoned HPP in favor of a microfiltration process.
Equipment suppliers are responding with validation research of their own. Hiperbaric is working with process authorities in the Netherlands to demonstrate the efficacy of HPP with low-acid products, and Avure commissioned a study at IFSH that concluded that C. bot cannot germinate and produce toxin in coconut water held at temperatures below 50°F for 45 days. Avure’s resident microbiologist plans to seek publication of the study’s methodology and conclusions in a peer-reviewed journal.
It remains to be seen if FDA accepts those findings or maintains its position that HPP processors must account for cold-chain abuse, even when it is the consumer who fails to properly refrigerate treated products. With almost half of the worldwide network of HPP presses operating in the U.S., FDA’s future direction could either encourage or put a chill on the most promising new pasteurization technology.