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Ozone in food processing and cold storage

The presence of numerous genera of spoilage bacteria, yeast and moles and a vocational pathogen on fresh produce has been resulting in several out breaks of diseases. Fruits, salads and raw vegetables have also been identified a causes of traveller’s diarrhoea. E-Coli is the most common cause of this illness. Outbreaks of salmonella infection have been attributed to consumption of contaminated tomato, beans, sprouts and watermelon. Gastroenteritis has also occurred by the consumption of raw onions, fresh cabbage and lettuce.

Like wise, methods of handling, processing, packaging and distribution of fresh produce have also contributed to microbiological contamination. Fruits and vegetables can be contaminated with pathogenic microorganisms while growing in the fields or orchards, or during harvesting, post harvest handling, process and distribution. Pathogens capable of causing human diseases include bacteria, viruses and parasites that are present in the water used for irrigation or in the soil in which they are grown.

The methods currently available for disinfection and sterilization are through the use of oxidative and non-oxidative Biocides. The most predominant is the use of chlorine compounds – generally hypochlorite. Fruits and vegetables not uncommonly contain population of 104 to 106 microorganisms per gram when they arrive at the packing house or processing plant. Only 1 to 2 log unit reduction can be obtained by washing with water. Using chlorine cannot be totally relied upon as a disinfectant for fresh produce as it has only about 1 to 2 log unit reduction of microorganism takes place. Even the use of trisodium phosphate (TSP) in wash water has not been found very effective and has been found to reduce microorganisms only to about 2-log unit reductions.

The disadvantages of non oxidative biocides are that the process of disinfection often may not be complete (in the concentrations used) or some bacteria may be resistant and the preferred procedure is the use of oxidative biocides. Using non oxidative biocides in food preparation is also limited in that they may impart some undesirable taste and cause problems in preparation such as frothing, etc.

Chlorine in any form though having been used for decades, has now been found to produce very toxic and carcinogenic by-products which create as much problem as it solve. Firstly, some organisms may survive even after the process as using higher concentrations which may be impractical may only kill them. Further, Chlorine itself imparts some flavour not accepted by consumers. Some other types of disinfectants have to be sourced. Hydrogen peroxide is one, which is now viewed as an alternative, in that it is a reasonable oxidant and the by-product is water, but the overall costs make it rather less attractive alternative.

Ozone has been used in disinfection of water for quite some time now, but it is only now that its use in food processing and cold storage has been recognized. A tri-atomic oxygen, Ozone has a very high Redox potential, only next to Fluorine. By virtue of this high Redox potential, Ozone is more than 3000 times powerful disinfectant than chlorine. Ozone is an eco friendly chemical gas that does not produce environmentally toxic by-products (chlorinated hydrocarbons for instance).

In the United States, a substance either has to be declared to be “Generally Recognized as Safe” (“GRAS”) by a recognized panel of food experts, or approved as a “food additive” by the U.S. Food and Drug Administration for its use to receive widespread acceptance.

Ozone, a few years back has been declared to be GRAS by a panel of food experts established by the Electric Power Research institute (the EPRI). This allows the unrestricted use of ozone in any food processing application other than meat, dairy, or poultry processing applications (ozone also has a number of applications in these industries which are regulated by the US Department of Agriculture).

The wide ranging possibilities for using ozone in the food industry and agriculture, as well as in other fields are created similarly by its bacterial and germ killing power. Not only does it act as a germicide but as a spore killing agent as well. Fruits and foodstuffs, exposed to its effect, undergo a more or less pronounced change as a consequence of its action on the vital process of cells, the process of there metabolism particularly, through the inactivation of their metabolic products. At the same time, it reacts with other materials present that can be oxidized and thereby it destroys fragrances and odours.

Objectives: Food Processing Process & Storage Treatment

Treatment of food for any application, whether for additional processing or direct distribution to consumers, has three primary objectives for consumers:

Objective 1 – Sanitisation

Food for human consumption must be free of pathogenic organisms. Contamination can occur from the harvesting stage, during transportation, during processing through water, equipment or the human element or even by cross contamination.

Objective 2 – Stop spoilage or over ripening

Food industry is global and hence it is practically impossible to reach the food to the consumers across the world in an unspoiled manner, ripe or nearly ripe. The customer would like to see the food fresh and in an undamaged condition. It must be free from bacterial or fungal contamination, free of foul odor and, taste .These standards alone will provide consumer satisfaction.

Objective 3 – Remove contaminants

Fungicid and pesticides used during farming can contaminate the surfaces of the food and this can be potentially dangerous .Of late, more consideration has been give to this factor .Removal or destruction of these contaminants is of prime importance.

Ozone in Cold Storage:

Utilization of the properties makes ozone eminently suitable for increasing the storage life of perishable foods in refrigerated premises. At the same time its use is economical, as the investment and operational costs of the equipment are on an acceptable level in relation to the size of the refrigerated rooms. Its application eliminates the risk of leaving the unpleasant odour or other traces of antiseptics used for preservation on food stuffs.

Utilization of ozone for increasing the storage life of food, particularly if held at low temperatures, is believed to have started in 1909 when, in the cold storage plant of cologne, the reduction in the germ count on the surface of meat stored there was observed after an ozone generator had been installed in the duct of fresh air used to ventilate the storage room.

Practical operations for preservation start with the sterilization of air in such a way that air entering the storage room contains a sufficient amount of ozone to destroy microorganisms. At the same time, however, ozone decomposition to a significant extent is to be expected due to the high moisture content required, the walls of the storage room, the packaging materials, the absorption effect of the stored goods, and also to the oxidation reactions taking place.

Washing in water can effectively remove sand, soil and other debris from fresh fruits vegetables but should not be relied upon to completely remove microorganisms.

During storage, ozone exerts a threefold effect by destroying the micro-organisms, oxidizing the odours and affecting the processes of metabolism.

Ozone’s primary action on molds is to suppress their growth and this effect can set in rapidly, particularly in the initial stage on a mold free surface. Afterwards this process leads to the destruction of cultures already formed. Ozone attacks immediately the easily accessible cells on the surface since ozone exerts a surface effect in the first place and has an only slight depth of penetration.

Ozonization applied for the storage of refrigerated meat destroys surface microorganisms, particularly the family of Pseudomonas responsible for spoilage.

Increasing the moisture content of the environment favourably influences the germicidal effect. This is brought about by the swelling of microbes making them more susceptible to destruction. Experiments conducted with beef showed that ozone is most efficient if the surface has a definite moisture content of around 60%.

Effect on odours

Ozone itself has a characteristic odour, yet the result of application does not mask odours.

Atomic oxygen formed by decomposition of ozone immediately oxidizes the differently smelling materials.

The characteristic putrid odour, however, remains and is difficult to eliminate even with the use of ozone. In general, the lower the temperature and the larger the molecules taking part in the reaction, the weaker is the oxidizing effect. The moisture content in the air has no effect on the process. At very slight concentration, say between 0.01 and 0.04ppm ozone, the air of the room of storage space is felt to be fresh and pleasant and no stuffy odour is sensed any more.

It is an established fact that the odour of aromatic fruits such as strawberries is enhanced in the presence of ozone. It is possible that the formation of fragrances and odours giving the fruit its characteristic flavour is assisted by ozone. The sterilization of the air in fruit stores by ozone prevents the odours of packaging materials from being transferred to the goods stored, a phenomena which frequently takes place otherwise, particularly when wooden crates are used in refrigerated stores at relative humidity of 85-90%.

V. Baratharaj, CMD,
Ozone Technologies and Systems Pvt. Ltd

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