Over the past 10 to 15 years, industry and the government have sought intervention strategies to reduce general microbial numbers and, specifically, to reduce or try to eliminate all produce pathogens. The most notable recent produce pathogen outbreak, which involved bagged baby spinach from California, was caused by E. coli 0157:H7. This occurrence resulted in a multistate outbreak, leading the U.S. Food and Drug Administration (FDA) to draft the “Guide to Minimize Microbial Food Safety Hazards of Fresh-cut Fruits and Vegetables.”
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One method for dealing with microbial food hazards is the introduction of biocides into produce processing waters. A critical component for most produce manufacturers, it can enhance or jeopardize food safety from the harvesting step through the production processes.
“Guide to Minimize Microbial Food Safety Hazards for Fresh Fruits and Vegetables,” an FDA Center for Food Safety and Applied Nutrition (CFSAN) guidance document published in October 1998, devotes a whole section to water as a microbial hazard, control of potential hazards, agricultural water, and processing water.
Processing water systems are the main focus of your direct intervention food safety approach and are more critical for fresh produce markets than any other food market segment. If the direct intervention and sanitation program at a produce processor ignores processing water treatment, it is not a complete program and pathogen issues will arise.
Water used for food product and food contact surfaces is in the good manufacturing practices (GMP) regulations in the Code of Federal Regulations (CFR); the specific sections are CFR Title 21 Part 110.37 and 110.80. Facilities that deal solely with raw produce commodities are exempt from some segments (see 21 CFR 110.19). Market pressures inherent in these produce markets encourage most raw produce processors to adhere to GMPs regarding water quality.
A Race Against Time
From the time produce products are picked until they are processed and/or consumed, the natural or artificial ripening and spoilage attributes of a specific product create a race against time. This push begins the moment a product is picked in the fields and continues through the ripening process.
Hydrocooling is one way to slow a product’s respiration and enhance shelf life, but not all produce commodities are hydrocooled. Those that are quite sensitive to wetting are usually air cooled. Water does, however, remove heat from a product roughly 15 times faster than air. All hydrocoolers utilize a water pump to put the warm product into contact with the chilled water. Some hydrocoolers use a refrigeration system, while others use block or crushed iced to cool the water supply.
Produce products with a large volume versus surface area—like sweet corn, apples, cantaloupes, and peaches—do well with hydrocooling. There are four types of hydrocoolers: conventional, batch, immersion, and truck.
In conventional hydrocoolers, the produce is placed onto conveyors in cartons/bulk bins that go into a chilled water shower. Cooling rates are based upon a belt speed of roughly one foot per minute, so the cooling capacity of a unit is largely dependent upon the conveyor belt length of the cooling zone. Water volume usages are fairly high, as much as 20 gallons per minute per square foot of active cooling area. Large production units like cooperatives use these types of hydrocoolers.
Batch hydrocoolers have no conveyors; instead, they create a cooling zone using palletized cartons or bulk bins. Depending on their size, these batch units will chill one to eight pallets at once. Some units use a hybrid system that employs air chilling as well as water chilling.
Immersion hydrocoolers are large, shallow, rectangular tanks that use recirculated, chilled water. Crates of warm produce are placed into the tank with a submerged conveyor. Either a refrigeration system or crushed ice keeps the water cold using a recirculation pump. An example of immersion hydrocooling is the bulk fluming of products like string beans prior to grading.