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DETERMINATION OF FACTORS CONTROLLING ACCURATE MEASUREMENT OF A w BY THE VAPOR PRESSURE MANOMETRIC TECHNIQUE
Author(s) -
LEWICKI P. P.,
BUSK G. C.,
PETERSON P. L.,
LABUZA T. P.
Publication year - 1978
Publication title -
journal of food science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 150
eISSN - 1750-3841
pISSN - 0022-1147
DOI - 10.1111/j.1365-2621.1978.tb09782.x
Subject(s) - reproducibility , evaporation , vapor pressure , chemistry , analytical chemistry (journal) , sample (material) , water vapor , temperature measurement , pressure measurement , drop (telecommunication) , vapour pressure of water , accuracy and precision , chromatography , thermodynamics , mathematics , statistics , telecommunications , physics , organic chemistry , computer science
The precision and reproducibility of the VPM method has been improved by the simultaneous measurement of water vapor pressure and temperature of the food sample. It has been shown that evacuation of the system substantially lowers food temperature due to evaporation of water. The drop in sample temperature is dependent on water activity of the material and is large at high water activities. Even at steady readings of the manometer, the temperature of the sample is not equal to room temperature. Therefore, calculation of water activity based on room temperature gives erroneous results which are significantly lower than the results based on the measured sample temperature.