Hygiene of Gasket Materials Used in Food Processing Equipment Part 1: New Materials

Abstract

Gasket materials used in the food industry were studied for their susceptibility to biofilm formation and their cleanability in cleaning-in-place operations. The materials included in the study were EPDM (ethylene propylene diene monomer rubber), NBR (nitrile butyl rubber, also known as Buna-N), PTFE (polytetrafluoroethylene) and Viton (fluoroelastomer). Stainless steel was used as a reference material. The experiments were performed with new (unused) materials in test conditions simulating dairy or brewing processes. Mixed cultures of Bacillus thuringiensis and Pseudomonas fragi or Pantoea agglomerans and Pediococcus inopinatus were used as test organisms and the cleaning-inplace was performed in an experimental test rig. The conventional plate count method, epifluorescence microscopy in connection with image analysis, and impedance measurements were used to estimate the amount of biofilm on test surfaces before and after cleaning. The susceptibility to biofilm formation was dependent on the process conditions simulated and varied between the different materials. PTFE was less susceptible in dairy conditions,whereas NBR was less susceptible in brewery conditions. The cleanability of both materials was as good as that of stainless steel when cleaning-in-place parameters typical both for dairies and for breweries were used. The methods used for detection of surface-bound bacteria and biofilm are discussed.