Microorganisms are present everywhere food is present and handled, from the fields in which agricultural crops are planted and raised to harvest, animal breeding and rearing houses to the facilities that process crops and animals, to packaging and food storage plants. Control of microorganisms, particularly pathogenic microorganisms (those that cause diseases in humans and animals), is important at all stages. Strong measures are necessary for microorganism control.
Classical chemical control methods based on chlorine or bromine compounds are effective for controlling microorganisms, but their use can result in halogenated byproducts being formed and these subsequently can be incorporated into the food product itself. Ozone, consisting only of oxygen atoms, is one of the strongest disinfectants available, and does not form halogenated byproducts. Additionally, ozone can be applied in the gas as well as aqueous phases, providing additional processing benefits. Uniquely, combining ozone with other materials (hydrogen peroxide or ultraviolet radiation) produces the very reactive intermediate, hydroxyl free radical, which is a stronger oxidizing agent than is ozone itself.
Ozone is both a strong oxidizing agent as well as a strong disinfectant. Because of this, both benefits (oxidation and disinfection) can be achieved during the single step of ozonation. When considering oxidation, however, one also must recognize that not all oxidizable substances can be totally destroyed even by ozone, the strongest oxidant and disinfectant commercially available. In most cases, oxidation reactions proceed through intermediate stages, arriving at CO 2 and water only when the pollutant is provided with a sufficient concentration of ozone for a sufficient period of time to allow complete oxidation (mineralization).
This point is very important in treating foods, which are organic in nature, with ozone. The indiscriminate over-use of ozone to control microorganisms can easily partially oxidize surface organic materials on the food being treated, and can change the nature of that food surface. The key to successful application of ozone for contacting foods is to add sufficient ozone to allow it to accomplish its intended purpose, but not enough to cause damage to the food itself. This requires testing and development of ozonation conditions to apply to specific food products.
Water is an essential processing agent in agriculture and food processing. It can be used in many instances to carry the ozone. Since water contacts foods, it is critical that it be as clean as possible. Due to the ever-rising costs of treating potable water, increasing economic pressure is being placed on reuse of processing water in food and agriculture applications. Ozone has a long and proven history of application in treating water and wastewater, and thus has many potential applications in agriculture and food processing facilities. Water containing ozone is being used in many food processing plants currently to spray or wash food products, and to wash processing and storage equipment.
Many agricultural products are stored after harvest, prior to packaging and sale. Gas phase ozone, applied properly with attention to concentration, relative humidity, and exposure times, can maintain low microorganism and insect levels in/on the product(s) during such storage, thus increasing storage life while maintaining high product quality – resulting in less product loss during storage.
A recent agricultural development in Switzerland involves the close to simultaneous application to crops of high voltage, pulsed negatively charged water, then an aqueous spray containing ozone, then high energy UV radiation (Steffen, 2005a,b; Rice and Steffen, 2005). This approach stimulates a reaction in growing plants termed “Systemic Acquired Resistance”. The result is that the growing plants do not need to be sprayed with pesticidal chemicals. Periodic application of this new Phyto3 Tech technology maintains plant cleanliness, free of pathogens, without the necessity of chemical sprays. This means no chemical residuals on the harvested products, and no chemicals washed into the soils.
Applications for ozone in food processing abound As reported in the July 2005 edition of Water Technology magazine, industry experts say the potential use of ozone in food-processing industries is likely to grow over time as food processors become more familiar with the technology and its capabilities. The Electric Power Research Institute (EPRI) has identified the following as some of the emerging applications:
1. Eggs. Sanitize whole shell eggs to eliminate potentially pathogenic bacteria.
2. Fruits and vegetables. Treat pre-process wash water for fruits and vegetables.
3. Poultry. Sanitize poultry chiller water to reduce potential pathogenic bacteria, and recondition overflow water for recycling and reuse (within US Department of Agriculture guidelines).
4. Wineries. Sanitize cold water, replacing traditional hot water and harsh chemical sanitation methods.
5. Grain. Using ozone as a substitute for chlorinated water to control bacteria and mold in grain processing.
6. Fish. Treatment of water in aquaculture tanks greatly reduces foaming even without purifying the water.
7. Seafood. Using ozone for seafood processing applications, including shellfish depuration, fish pumps, fillet-line spray bars and surimi mixing tanks.