| Visual inspection, ultraviolet (UV) fluorescence with visual inspection, three rapid swab methods, liquid extraction followed by measurement of total protein in the extract, total nitrogen analysis with a nitrogen analyzer, light microscopy, and Fourier-transform infrared (FTIR) spectroscopy were investigated for their usefulness in measuring dairy food soil residue on spray dryer filter bags. The rapid swab methods used were the AccuPoint ATP bioluminescence-based device, the Pro-tect protein-based device, and the SpotCheck Plus gIucose/lactose-based device. The nitrogen analyzer was the most useful technique for measuring dairy food soil residue on filter bags, because of its sensitivity, speed and robustness. Light microscopy and FTIR spectroscopy were found to be valuable adjunct techniques for confirming nitrogen analyzer results, and for investigating the types and distributions of residual soil present on filter bags.; The distribution of residual soil on clean-in-place (CIP) cleaned spray dryer filter bags was also investigated. A significant (p < 0.0001) trend was found whereby residual soil levels increased as one moved down a filter bag from top to bottom. Five sub-samples appeared to be adequate for determining the overall cleanliness of spray dryer filter bags. |
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