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Introduction

In an increasingly regulated and safety-conscious market, the sugar processing industry has to meet ever more stringent standards of quality. Concentrated sugar syrups have a high osmotic pressure, and although this prevents microorganisms from growing and reproducing, they can still survive in spore form and may grow once the syrup is diluted. Microbial growth can cause food discolouration, off flavours and shortened shelf-life of sugar-based products, as well as increasing the risk of infection and ill-health. The threat of contamination is further increased as manufacturers respond to consumer demand for reductions in chemical additives and preservatives.

A non-chemical method of controlling microbial contamination which is gaining increasing acceptance is ultraviolet (UV) disinfection. UV kills all known food spoilage organisms, including bacteria, moulds, viruses and their spores. It is a low maintenance, environmentally friendly technology which eliminates the need for chemical treatment while ensuring high levels of disinfection.

How UV disinfection works

UV is the part of the electromagnetic spectrum between visible light and X-rays. The specific portion of the UV spectrum between 185-400nm (known as UV-C) has a strong germicidal effect, with peak effectiveness at 265nm. At these wavelengths UV kills microorganisms by penetrating their cell membranes and damaging the DNA, making them unable to reproduce and effectively killing them.

A typical UV disinfection system consists of a UV lamp housed in a protective quartz sleeve and mounted within a cylindrical stainless steel chamber. The liquid to be treated enters at one end and passes along the entire length of the chamber before exiting at the other end. Virtually any liquid can be effectively treated with UV, including viscous sugar syrups, raw municipal water, filtered process water, beverages and effluent.

There are two main types of UV technology, based on the type of UV lamps used: low pressure and medium pressure. Low pressure lamps have a monochromatic UV output (limited to a single wavelength at 254nm), whereas medium pressure lamps have a polychromatic UV output (with an output between 185-400nm).

Benefits of UV Disinfection

UV disinfection has many advantages over alternative methods. Unlike chemical treatment, UV does not introduce toxins or residues into process water and does not alter the chemical composition, taste, odour or pH of the fluid being disinfected.

UV treatment can be used for primary disinfection or as a back-up for other purification methods such as carbon filtration, reverse osmosis or pasteurisation. As UV has no residual effect, the best position for a treatment system is immediately prior to the point of use. This ensures incoming microbiological contaminants are destroyed and there is a minimal chance of post-treatment contamination.

UV applications in liquid sugar manufacture

Liquid Sugar Syrup
UV can eliminate all yeasts and moulds commonly responsible for taste and flavour problems in sugar solutions. As sugar syrups have a high density, they have a low UV transmission. To ensure adequate exposure, UV systems for sugar treatment have to be equipped with high intensity, medium pressure lamps – low pressure lamps are not suitable for this application. The systems are usually installed in-line after the storage tank discharge point, so the syrup is treated prior to dilution into the food and beverage, but prior to the addition of additives, flavourings or colourings, all of which reduce UV transmission.

Tank Headspace
Modern hot dissolving systems can leave the headspace above the syrup in the mixing and storage vessels as an ideal growing environment for spoilage organisms. Condensation containing microorganisms forms on the tank surface and can drip off the inner wall of the vessel resulting in surface growth and infection of the syrup. The Hanovia UV-I (UV-Immersion) range overcomes this problem by disinfecting the air drawn into the tanks when the liquids are drawn off. Mounted on the ceiling of the vessel, it provides continuous disinfection of the tank headspace. The UV-I is fully immersible in the syrup, eliminating the problem of having to monitor liquid levels.

Water Supply
Although municipal water supplies should be relatively free from harmful microorganisms, this should not be assumed - they will also contain naturally occurring moulds and yeasts. In addition, water from private sources such as boreholes could well be contaminated. UV treatment of all incoming water supplies ensures all contamination is stopped at source. It also allows the re-use of water, improving availability and plant productivity without risking the quality of the product.

CIP Rinse Water
The final rinse water of the CIP should be the purest source water available, but may contain microorganisms. If chemical sterilisers are used, solutions can remain in pipework, tankers and tanks, where they can mix with the incoming product and may produce a taint. UV treatment of rinse water is better as it is unaffected by acid or alkali in cleaning fluids, is compatible with hot detergent and leaves no taint. In addition, it is extremely cost effective and safe.

Filter disinfection
Stored reverse osmosis (RO) and granular activated carbon (GAC) filtrate can be a breeding ground for bacteria. UV is an effective way of disinfecting both stored RO and GAC filtered water and has been used in the process industries for many years.

Dechlorination
GAC filters are also often used to dechlorinate process water, removing the ‘off’ flavours often associated with chlorine disinfection, meaning the flavour of the final product remains untainted and free from unwanted flavours or odours. Placing UV systems ahead of GAC filters used for dechlorination improves the performance of the filters and results in longer carbon runs, so decreasing operating costs.

Effluent
Effluent from beverage manufacturing facilities can be treated without the use of environmentally hazardous chemicals. This ensures all discharges meet with local environmental regulations. As already mentioned, because process water can be treated and re-used with UV, this also leads to a significant reduction in the amount of waste water produced.

Ventilation Ducts
Air conditioning and ventilation systems are prime sources of contamination from air-borne spoilage organisms. The increasingly strict standards for cleanliness are not always met by air filtration alone, and it is now common to use UV in conjunction with, or instead of, sterile filters in air ducts.

Conclusion

Meeting the ever-more rigorous standards required in the production of liquid sugar is a real challenge for manufacturers. If improvements need to be made to plant and equipment, they need to bring quick returns on the investment and measurable improvements in product quality.

For those manufacturers seeking to improve the quality of the end product, UV is an economic, realistic option. It is a well-known and trusted technology in industries ranging from pharmaceutical, food and microchip manufacturing to swimming pool and drinking water treatment. It is one of the most effective methods of ensuring consistently high levels of disinfection and has been adapted for many situations.

UV disinfection systems are easy to install, with minimum disruption to the plant. They need very little maintenance, the only requirement being replacement of the UV lamps approximately every 12 months, depending on use. This is a simple operation that takes only a few minutes and can be carried out by general maintenance staff.