Ultraclean protection keeps contaminants out

Feb. 7, 2001
French food processors move beyond clean rooms to help guarantee product purity.

Filling machines for sensitive drinks operate under an isolator.

One of the major problems in the food-processing industry today is protecting against microbiological product contamination from bacteria such as Listeria, Salmonella, Escherica Coli, and Clostridium. These are generally spread by ambient air, room surfaces, machinery, and workers. The challenge is to eliminate pathogenic micro-organisms while preserving the flavor of foods.

In France over the last decade, companies involved in aerospace, microelectronics, and pharmaceutical sectors began offering clean-room technology for the food-processing industry. Today, French food manufacturers routinely use ISO 7 or ISO 8 clean rooms in cutting, bottling, and packing rooms. These permanent installations require three categories of equipment: an air-treatment system, diffusion system, and a specific envelope that individualizes the clean room, explains Bernard Gaffet, president of the Association for the Prevention of and Research into Contamination (ASPEC).

Generally, air treatment units provide a positive pressure (60 Pa) for sensitive areas and replace air at a certain flow rate while controlling temperature and humidity. A series of filters (prefilters, high efficiency, and very-high efficiency) remove the bulk of the dust inside the clean room. Air ducts of polyester resin or stainless steel distribute the air. Finally, ceilings, floors, walls, and special airtight windows maintain the air at a positive pressure.

Technological limits
"These controlled environment rooms encounter three big constraints in the manufacture of food products," observes Pascale Coffinier, a French food-processing engineer who specializes in air contamination. First, high-production rates and numerous human interventions can disrupt the ventilation in traditional clean rooms. The operating staff often has difficulty respecting the many strict procedures, such as appropriate clothing and air locks. Finally, frequent cleaning and the resulting relative humidity can damage clean-room equipment, including treatment units, filters, and ducts.

These drawbacks, combined with high costs, make the case for new "close-protection" technology. This concept is currently being developed by several companies and the Ultraclean, Nutrition, Industry, Research Assn. (UNIR), in cooperation with the Ministries of Agriculture, Industry and Research.

"The mini-environment is a solution for the treatment of localized problems, whereas clean rooms are suitable for global problems," explains ASPEC's Gaffet. This is why French manufacturers are developing techniques for the agro-food industry that treat the air near equipment used for packaging sensitive products such as milk and noncarbonated drinks, rather than the entire room. This permits a considerable reduction in the size and power consumption of the air-treatment equipment. Contamination control takes place at the product level, which makes it possible to improve process efficiency. Here's a look at some recent developments.

Air curtains
This equipment consists of textile ducts made from fabric fitted with transparent flexible skirts. The French company Fouchard, a specialist in air conditioning and conveyors, has developed a close-protection conveyor system through diffusing textile ducts. The unit generates unidirectional vertical airflows consisting of slow air jets (0.3 to 0.5 m/sec) bordered by fast air jets (0.8 to 1 m/sec). These prevent contaminated air from entering the production area and onto the food products conveyor. The result is ISO class 5 air purity on the conveyor belt while reducing flow from the airtreatment unit and air-cooling requirements. "This device can be adapted to existing processes and produces a saving of 30% in costs and maintenance compared with clean rooms," adds Pascal Jaluzot of UNIR.

Side diffusion
The National Center for Agricultural Machinery, Agricultural Engineering, Water and Forestry (CEMAGREF) has developed a progressive flow system for the localized protection of food-processing equipment. A system of metal nozzles fitted on one side of a conveyor produces a graduated airflow that sweeps horizontally across the work surface of a conveyor belt. The air returns and is drawn in on the opposite side of the conveyor, providing an airflow protective zone 4 in. high. The operator can intervene in this protected zone to remove a product without contaminating neighboring products.

The system can be applied to any type of installation, with size depending on the area to be protected. "The diffusion of air is provided by an easily cleanable, perforated stainless-steel section," says Georges Arroyo of CEMAGREF. In addition, the metal section was developed to avoid drawing in contamination from the surrounding air, and to ensure even distribution of the airflow. The vertical airflow nozzles have a profile that provides slow flow in the center and fast flow at the sides of the protection zone, with the fast flows acting as a dynamic bacteria barrier.

Diffusing ceilings
The French manufacturer Clauger, located in Brignais, specializes in industrial refrigeration and process air conditioning. At the leading edge of environment control and air contamination is a diffusing ceiling. "Diffusion systems are designed for laminar-flow dust removal workstations," explains Richard Vallin of Clauger. The ceiling consists of an air-distribution system and a diffusing fabric that ensures completely laminar airflow. With the help of this technique, absolute filtration is incorporated in the air treatment unit. The entire assembly is placed above the close-protection unit. Constructed from 316 stainless steel, the ceilings are washable. In addition, attaching a side skirting provides guidance for the air when there is considerable distance between the ceiling and product.

La CalhEne, a leading isolator manufacturer, has adapted technology from the nuclear industry with a product for the food and packaging industry. "This innovative device enables close containment and aseptic transfers, particularly in filling or cutting lines," explains Philippe Fontcuberta. Already, 12 filling lines for drink products running at rates from 10,000 to 40,000 bottles /hr, a line for prepared meats, and five pilot and validation facilities have been equipped with this new technique.

The isolator consists of several components. The enclosure can be flexible (PVC film for example) or rigid (stainless steel) and acts as a physical barrier. A ventilation and filtration system maintains positive pressure inside the isolator, providing germ-free air circulation at a rate of 20 to 50 replacements/hr. An atomizer system (paracetic acid, hydrogen peroxide, or more complex mixtures) sterilizes the internal environment of the isolator, while gloves attached to sleeves or half-suits enable operator manipulation. "We have developed a system with airtight transfer double doors that allow the introduction of packaging and the tools necessary during production without the risk of breaching the containment," says Fontcuberta.

Information for this article provided by the French Technology Press Office, Chicago.

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