Localisation, dénombrement et identification de la contamination microbienne après nettoyage de joints en EPDM d'un circuit de pasteurisation de l'industrie laitière

Abstract

Microbial contamination after cleaning and wear of gaskets introduced in four places in a milk pasteurization process line were studied during 1-, 4-, 16-and 20-week periods. From the fourth week onwards, gaskets presented signs of wear and fouling, visible to the naked eye and increasing with time. Observation of 20-week gaskets using scanning electron microscopy showed a residual fouling depending on processing conditions. Organic fouling was generally higher on the gasket-metal contact area than on the face exposed to circulating fluids. It was made up of closely-associated milk and microbial fouling. Microbial contamination after cleaning was detached using sonication and cells were enumerated by different methods. Acridine orange direct counts showed a stabilized total population beyond 106 cells per centimeter of gasket perimeter. The methods used to assess culturable cells showed an increase of this population with time, reaching 103 cells per centimeter of gasket perimeter for the four places after 16 or 20 weeks, made up of typical raw milk micro-organisms.