Use of Ozone to Improve the Safety of Fresh Fruits and Vegetables
In recent years, increasing attention has been focused on the safety of fruits and vegetables, and in particular on the intervention methods to reduce and eliminate human pathogens from fresh produce.
Traditional technology utilizes water with or without a sanitizing agent to wash fresh fruits and vegetables. Chlorine is the most widely used sanitizing agent available for fresh produce, but it has a limited effect in killing bacteria on fruit and vegetable surfaces. The most that can be expected at permitted concentrations is a 1 – to 2-log population reduction (Sapers, 1998). Furthermore, the environmental and health communities have expressed concerns about the residual by-products of chlorine.
An alternative treatment is being sought to improve food safety. Research and commercial applications have verified that ozone can replace traditional sanitizing agents and provide other benefits (Bott, 1991; Cena, 1998; Graham, 1997). Many research and industrial trials are underway to validate the use of ozone in the produce industry. Several meetings on this topic have been sponsored by the Electric Power Research Institute (EPRI), including a “Conference on Ozone for Processing Fresh-Cut Fruit and Vegetables” in April 1998 and an “Ozone Workshop” in May 1998. The produce industry is very interested in this technology. However, many questions still have not been resolved, since experience in commercial application in the United States is lacking (Graham, 1997).
Seeking an Alternative to Chemical Sanitizers
In the past two decades, the consumption of fresh fruits and vegetables in the U.S. has dramatically increased. In the meantime, the incidence of food borne illness due to food pathogens, chemicals, and wastewater has greatly increased. The has been drawing significant public and government attention.
The number of produce-associated food borne disease outbreaks and the number of cases of illness due to food pathogens have significantly increased in recent years (Tauxe et al. 1997). Moreover, losses in the fresh produce industry that are attributable to microbial spoilage between the time of harvest and consumption are estimated to be as high as 30% (Beuchat, 1991).
Chlorine is commonly used in the fresh fruit and vegetable industry to improve microbiological quality and control pathogens. However, many research studies have indicated that it is limited in its ability to kill bacteria on fruit and vegetable surfaces (Bott, 1991; Cena 1998; Graham, 1997; Rice et al. 1982; Sapers, 1998). Environmental and health organizations have expressed concerns with traditional sanitizing agents with respect to the formation of by-products, such as trihalomethanes (THMs) and other chemical residues formed in the wastewater returned to the environment (Anonymous, 1998; Cena, 1998; EPRL, 1997; Graham, 1997). The produce industry is concerned about the possibility of future regulatory constraints on the use of chlorine as a sanitation agent.
Large amounts of pesticides have been used annually to control insects on fruits and vegetables (Ong et al., 1995). Current technologies cannot totally destroy the chemical residues on the surface of fruits and vegetables. These chemical residues may react with pesticides to form chemical by-products. These residues ultimately will be consumed by customers and may directly and indirectly affect public health. An accumulation of toxic chemicals in the environment has increased the national focus on the safe use of disinfectants, sanitizers, bleaching agents, and other chemicals in the food processing industry.
The produce industry is one of the largest and most important contributors to the world economy. It also generates billions of gallons of wastewater annually, with very high concentrations of bio-chemical oxygen demand (BOD) and chemical residues each year in the U.S. These waste waters have been linked to many serious problems such as cancer, fish death, water pollution, psychological and physiological diseases, and ecosystem damage. Moreover, the produce industry is paying heavy charges and surcharges for discharging wastewater into public water and wastewater treatment systems (Carawan, 1999).
In response to the public concerns about food safety, the President of the United States and Congress issued a new federal initiative in 1997 – the President’s Food Safety Initiative – to improve the nation’s food safety system and our environment. One of the approaches to improve food safety is to identify an alternative sanitizer to replace traditional sanitizing agents which can also be used to treat or recycle food processing wastewater.
Research and commercial applications have indicated that ozone can replace chlorine with more benefits. In 1997, ozone was self-affirmed as Generally Recognized As Safe (GRAS) as a disinfectant for foods by an independent panel of experts sponsored by EPRI (Graham, 1997). This self-affirmation was timely for the produce industry in light of the President’s Fruit and Vegetable Safety Initiative. The produce industry is very interested in the use of ozone and would like to know how, when, and where to apply it.
The potential utility of ozone in the produce industry depends on the fact that as an oxidizing agent, it is 1.5 times stronger than chlorine and is effective over a much wider spectrum of microorganisms than chlorine and other disinfectants. Ozone kills bacteria such as Escherichia coli, Listeria, and other food pathogens much faster than traditionally used disinfectants, such as chlorine, and is free of chemical residues (Langlais et al., 1991; Sapers, 1998).
Ozone is a high-energy molecule. Its half life in water at room temperature is only 20 minutes, and it decomposes into simple oxygen with no safety concerns about consumption of residual ozone in the treated food product (Graham, 1997). It can also be used for recycling water (Anonymous, 1998; Perkins, 1997).
Fresh fruits and vegetables are washed first by ozonated water, and the wash water can be recaptured and treated by a combination of ozonation and filtration. The treated wash water is free of bacteria, color, and suspended solids and can be recycled to reduce water usage. Unlike conventional chlorine-based washing systems, wastewater discharged by an ozonation process is free of chemical residues, a growing concern related to the environment and groundwater pollution (Anonymous, 1998). Ozone can also destroy pesticides and chemical residues, such as chlorinated by-products (Landlais et al., m1991).
Gaseous ozone is a strong sanitation and fumigation agent and can be used to sanitize foods in the storage room and during shipping to percent bacteria, mold, and yeast on the food surface and to control insects. It can eliminate undesirable flavor produced by bacteria and chemically remove ethylene gas to slow down the ripening process, thus allowing extended distribution (Rice et al., 1982).
For decades, it has been known that ozone is an effective disinfectant and sanitizer for the treatment of food product. It is commonly used in Europe for treatment of public water systems and food processing. It is being used in the U.S. for bottled water and has the potential for use in many food processing applications. Numerous documents and studies confirm the benefits of ozone applications in the food industry (Graham, 1997; Rice et al., 1982). Thus, ozone can successfully replace traditional sanitizing agents to control food pathogens.
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