Use of water activity characteristics enables a simplified approach for defining the reference moisture condition for FDA cocoa powder in-house reference material.
The Food and Drug Administration uses water activity behavior characteristics when adjusting test portion mass to correct for the moisture condition of its cocoa powder in-house reference material. The cocoa powder's moisture condition, and therefore weight, equilibrates according to the relative humidity (RH) of its surroundings. This process is predictable and defined by an isotherm. The reference values in the certificate of analysis are relative to the material's condition at 30% RH, which is assumed to be mid-range for typical laboratory settings. Since mass variations are relatively small within a 15-50% RH range, the mass may be measured immediately after removing a test portion from a storage bottle and used without correction if a standard uncertainty of 0.7% is acceptable for the mass. If greater accuracy is needed and the laboratory RH is known, a very simple and quick procedure can be used whereby the test portion is left open and exposed to the laboratory air overnight before weighing. After applying a correction, the standard uncertainty for mass measurement drops to 0.3%.
Division of Bioanalytical Chemistry, Office of Regulatory Science, Center for Food Safety and Applied Nutrition, US Food and Drug Administration, 5100 Paint Branch Parkway, College Park, MD, 20740, USA, william.cunningham@fda.hhs.gov.
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D002099:Cacao / Q000737:chemistry; D002623:Chemistry Techniques, Analytical / Q000379:methods / Q000592:standards*; D006813:Humidity; D011208:Powders / Q000737:chemistry; D012015:Reference Standards; D014481:United States; D014486:United States Food and Drug Administration; D014867:Water / Q000737:chemistry*
D011208:Powders; D014867:Water