Probably the greatest fear of an engineer in the food and beverage industry is contamination due to bacteria. Pseudomonas, Listeria, Salmonella, it doesn’t matter: they can all lead to product recalls, plant shut down and, most importantly, loss of reputation. Hygiene and disinfection of food-contact surfaces and equipment is paramount. The first choice of disinfectant is usually sodium hypochlorite (bleach). It is an oxidizing biocide that is readily available and well understood, however, its very ubiquity has led to concerns that some pathogenic bacteria, such as Aeromonas and Bacillus cereus are showing signs of resistance. Alternative biocides are available but most are less easy to handle than sodium hypochlorite and may raise health and safety concerns. There is one alternative that has been around for many years but, until recently, has been little used in the food processing industry: ozone.
Food and beverage facilities typically use chlorinated water not only for automatic cleaning in place (CIP) procedures but for manually washing down working surfaces, conveyors and other items of equipment which are not covered by CIP. Ozone has proved a superior disinfectant in both applications. Ozone dissolves in water forming a free hydroxyl radical which is a very powerful antimicrobial agent. Produced from oxygen by a high frequency silent electrical discharge, ozone has been used for the disinfection of drinking water for well over a hundred years. Ozone isn’t new to the food processing industry either. A study by Kim et al showed the effect of dissolved ozone in a batch reactor on Listeria monocytogenes. Dissolved ozone at 0.4 and 0.8mg/l inactivated 4.6 and 5.7 log CFU/ml within 30 seconds. A later study demonstrated that higher dissolved ozone concentrations gave faster (immediate) inactivation of the bacterium – much quicker than bleach. Ozone is also very effective at removing biofilms by rapidly oxidizing the extracellular polysaccharides that give biofilms their adherent nature. A major benefit of ozone for the food industry is that it decomposes rapidly to form oxygen, leaving no residues.
In the past, ozone generators were large, fixed items in the process plant with health and safety issues and were expensive in capital cost. Evoqua has included in its proven ozone range a small, portable system, the PC Series disinfection system, that can provide ozonated water instantaneously anywhere in the food processing factory simply by connecting it to a water supply. The all stainless steel disinfection system incorporates an on-board oil free air compressor which delivers air to an oxygen concentrator. This passes through an air-cooled ozone reactor with adjustable output. The ozone gas is then injected and dissolved into the flow of water delivered by an integral booster pump to a connected hose and nozzle system. It also includes an off-gas destructor to ensure that no ozone gas is discharged into the workplace.
A recent incident involving listeria at a large food processing facility in Europe resulted in an emergency telephone call to Evoqua who managed to deliver a PC Series disinfection system. Before the customer started using the mobile ozone system, they used chemicals for sanitisation, but couldn’t deactivate the bacteria. Since the introduction of ozone no listeria has been detected. The use of ozone has made the products safer, enhanced the shelf-life for the fresh produce and protects the company’s brand, it has also proven to be more economical than the use of chemicals. Employees also gained a safer working environment as the ozone removed slippery biofilm from the floor, and they noticed reduced smells in the factory.
This experience is supported by studies undertaken by the Norwegian Institute of Water Research (NIVA). They grew biofilms of Listeria monocytogenes on plastic and steel surfaces in the laboratory. The surfaces were then exposed to ozonated water, either by immersion or by flushing. After treatment with ozonated water, no viable bacteria were found.
In addition to the mobile ozone range for manual washdown, Evoqua’s fixed ozonation systems are easily integrated into CIP and product water systems. Several studies suggest that ozonated water is very effective at destroying most bacteria and viruses. In short, ozone is an excellent alternative especially where there is evidence of bacterial resistance to sodium hypochlorite and can be easily applied to equipment and work surfaces in all food and beverage sectors from vegetable and salad packaging to biscuit baking, brewing and soft drinks.
Featured in Food Processing May 2020 issue, page 12.
[i] Kim J G et al Application of ozone for enhancing the microbiological safety and quality of foods: a review J Food Prod. 1999 Sep;62(9):1071-87.
[ii] Kim JG, Yousef AE.. Inactivation kinetics of foodborne spoilage and pathogenic bacteria by ozone. J Food Sci 2000 65:521-528.