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Reversibility of Water Vapor Sorption by Cottage Cheese Whey Solids

Dairy Products Laboratory, Eastern Regional Research Center, Agricultural Reseach Service, United States Department of Agriculture, 600 East Mermaid Lane, Philadelphia, PA 19118^,3

ABSTRACT

Desorption isotherms for water vapor from cottage cheese whey solids vary with the way water is first sorbed by the whey solids. When water is sorbed progressively in small increments between zero pressure and saturation pressure, the powder becomes more porous during lactose crystallization. Subsequent desorption data follow a sigmoid pattern as a function of relative pressure. More water is desorbed from the powder than could be removed by evacuation before exposure to water vapor. Lactic acid also is desorbed from the whey solids under these conditions.

A sigmoid desorption isotherm representing higher moisture contents at all relative pressures is obtained when moisture sorption is accomplished in a single step at or near the saturation pressure. The latter type of desorption is considered more representative of the dehydration process in powder manufacture as moisture versus vapor pressure data for whey concentrates adhere closely to this isotherm. Cottage cheese whey concentrates contained more moisture than Cheddar cheese whey concentrates at the same relative pressure.

¹ Present address: Lipid Nutrition Laboratory, Nutrition Institute, Agriculural Research Service, United States Department of Agriculture, Beltsville, MD 20705.

² Present address: Consumer and Food Economics Institute, Agricultural Research Service, United States Department of Agriculture, Hyattsville, MD20782.

³ Research while Dairy Products Laboratory was in Washington, DC.