Ultrasound improves conveyer cleaning, says study

The study, by the University of Helsinki, found that ultrasonic cleaning was effective in reducing the Listeria monocytogenes from polypropylene, acetal, and stainless steel belt surfaces. Tougher hygiene regulations are forcing processors to perform more stringent washdowns of machinery and equipment. This in turn is encouraging the development of more efficient methods of cleaning. Utrasound treatments use high frequencies, usually at around 20 kHz, to pass through cleaning liquids and collapse bubbles, releasing energy that kills bacteria. And, Listeria monocytogenes are a particular problem for food processors because a small concentration of organisms can cause illness in humans and current detection methods are complex and time consuming. Tests were conducted on all of the belt materials at 30C and 45C (86F and 113F) over 30-second and 60-second periods. Two widely used cleaning detergents, potassium hydroxide (KOH), and sodium hydroxide (NaOH) combined with KOH, were also used during the study. The conveyor belt materials were contaminated with milk-based soil and various L. monocytogenes strains and then incubated for 72 hours to attach bacteria to surfaces. The study found that ultrasonic cleaning treatments reduced L. monocytogenes counts on stainless steel from 4.61 to 5.90 log units, while on acetal the counts fell from 3.37 to 5.55 log units, and from 2.31 to 4.40 log units on polypropylene surfaces. The results also found that tests combining ultrasound with cleaning treatments containing potassium hydroxide were significantly more effective. The logarithmic reduction was significantly greater in stainless steel than in plastic materials, the study said. It added that higher temperatures improved the cleaning efficiency in tested materials, although no significant difference occurred between cleaning times.