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The rate of soil removal and its nature were studied with a small commercial high-temperature short-time pasteurizer. The commercial recirculation system was altered to provide a single pass of cleaning solution through the equipment to observe progress of cleaning. A composite of the first 38 liters was taken after 1.5 minutes. Subsequent samples were taken after 3, 6, 22 and 21 to 22 minutes. Cleaning solutions were analyzed by centrifugal fractionation, solvent extraction, gas liquid chromatography, thin layer chromatography and infrared spectroscopy to determine the composition of residue and rate of its depletion.
Results showed both the nature of the tenacious material and the rate of removal. Triglycerides were the predominant material in the tenacious residue, which resisted removal by circulation cleaning. Triglycerides were in solutions taken after several minutes of cleaning. Triglycerides per se were removed during cleaning, thus contradicting the concept that saponification is an integral part of the cleaning process. The sensitivity achieved indicated the potential application of instrumental methods for evaluating cleanliness of food processing equipment.