Factors Influencing Tenacity of Dried Milk Films Exposed to High Humidity1,2

Abstract

Rinsability of milk films on stainless steel was impaired by exposure to 100% relative humidity (RH). Rinsability was determined by automated Lowry protein tests of detergent used to remove films. Residue of milk films was 1% of the initial soil load when dried on stainless steel plates without humidification, but was 6.35% of the initial load after drying (30 min), humidification (15 min) and redrying (30 min) all at 37 C. Three successive exposures to 100% RH for 7.5 min at 37 C, each followed by 30 min of drying, yielded a residue of nearly 30% of the initial soil load. Exposure at 37 C produced the maximum amount of residue on plates. Experimental temperatures ranged from 0 to 75 C. Temperature of milk applied to plates was of little importance. Raw milk formed more tenacious film than skim milk or major components of milk. Milk produced during colder months yielded less soluble films than milk produced during warmer months. Lowering of milk pH to 5.7, adding soluble calcium, and aging milk at 0 C increased residues. Chelation of soluble calcium with EDTA or dissociation of milk protein with sodium dodecyl sulfate decreased soil residue levels. Exposure of instantized nonfat dry milk to the high humidity treatment decreased its solubility more than tenfold.