Thursday, May 14, 2009


Modern world depends on 'air conditioning' technology to get relief from cold or hot weather conditions and dramatic developments have taken place over the years in the design of such systems both at the house-hold level as well as industrial scale. Basically the objective is to reduce the temperature of an enclosed space through production of 'refrigerated' air and its circulation. Cost of air conditioning is mainly for the power the system uses for the compressor and the diffuser and is considered a disincentive for many people to go for investment in this area. Continuous developments are taking place in improving the efficiency of air conditioners and to day's air cooling technology is far superior to what it was even a decade ago. One of the drawbacks of air conditioning for use in preserving food is the tendency for it to reduce the humidity leading to unwanted dehydration over a period of time. Of course there are special systems that can also compensate for humidity loss. As the temperature range for an air conditioner is 15-23 C, it can extend the life of perishable foods for only a couple of days at the most.

The "controlled air" technology is the core of Controlled Atmosphere Storage (CAS) and packing (MAP) where the air composition is changed to reduce oxygen and increase CO2 so that the microbicidal property of CO2 is exploited. In respiring and transpiring materials like fresh produce, the air composition is continuously manipulated to keep the material fresh without "aging" by removing gases like ethylene, excess CO2 and infusing oxygen at optimum levels. Combined with refrigeration, MAP and CAS can extend the shelf life of perishables like fish, meat, fruits, vegetables and flowers significantly. High capital investment and large scale systems that are available to day make it difficult for this technology to be adopted in countries like India in a massive way.

It was the food science group in University of Wisconsin which developed an effective technology for NASA in nineteen nineties for extending the life of fruits and vegetables taken in the space vehicles under the space exploration projects for scientific studies. Though the rarefied atmosphere in the outer space cannot support any life including that of spoilage microorganisms, the oxygen enriched environment within the space craft, created for the comfort of the astronauts was ideal for microorganisms to thrive. As it was difficult to maintain any CAP or MAP system that could have extended the life of perishable materials like fruits and vegetables, NASA was forced to look out for alternative technology for achieving the purpose. Limited room available in the spacecraft called for a system that does not need much space, light in weight and low on energy consumption. Out of this necessity was born the NASA technology for food preservation using "conditioned" air aptly called AeroCide technology or 'enconditioning technology' which involves using air to kill microorganisms in the environment where food is kept. The scientific principle behind the technology is based on the ability of ultra violet rays (UV) to generate hydroxy radicals over a Titanium dioxide(TiO2) surface which kills all microorganisms including bacteria, mold, yeast and virus.

The system generally consists of a chamber containing thousands of tiny glass tubes coated with TiO2 on which UV light is shone and all air borne particles become surface bound, not being able to float around. Particles like bacteria get disintegrated and are no more viable to be of any harm. The air passed through the chamber is sterile and can be used for preservation of food products. During conditioning of the air, hydroxy radicals and super-oxide ions also react with volatile organic compounds that can taint foods. Removal of ethylene in the AeroCide chamber delays ripening and senescence, extending the effective life of cut flowers, fruits and vegetables for 2-3 weeks. The technology is widely being used in the last two years by the horticulture, floriculture and health care industries. Major food players like Del Monte, Coke and many hospitals in the US are already using the system for some of their operations. High refraction rate and photo catalytic reactions help to reduce the power consumption dramatically. The low maintenance cost is another USP of the system as it requires only a bulb to be replaced occasionally. Absence of air filters and no necessity to clean up the system periodically further recommend this technology for food industry. Enconditioners are available in India in capacities varying from 3000 cubic feet of air to 20000 cubic feet air treatment. According to the dealers in India a 5000 cubic feet air treatment capacity enconditioner will cost just Rs 1 lakh which can be installed easily in a few minutes in the room where air is to be sterilized.

While enconditioners can be had for a small investment, deploying it for food preservation calls for design of treatment systems for different foods. While for general air sterilization the compact units are suitable for protecting environment in houses, offices, factories, store houses, restaurants etc and cutting down over all microbial load, combination of CAS and AeroCide technologies can be much more effective than either of them singly when it comes to food preservation on a large scale. Probably passing the gas mix in CAS system through the enconditioner before entering the storage chamber may provide a better hygienic atmosphere in such ware houses supplementing the efficiency of CO2 as a germ killer. It has also the added advantage of removing ethylene from the circulated air, retarding ripening and senescence significantly and destroying product specific aromatic volatiles that emanate from different sored products in a mixed CAS ware house.


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