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Measurement of Water Activity of Salt Solutions and Foods by Several Electronic Methods as Compared to Direct Vapor Pressure Measurement
Author(s) -
STAMP J.A.,
LINSCOTT S.,
LOMAURO C.,
LABUZA T.P.
Publication year - 1984
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.1365-2621.1984.tb10413.x
Subject(s) - chemistry , vapor pressure , analytical chemistry (journal) , salt (chemistry) , water vapor , cutoff , linear regression , statistics , chromatography , mathematics , organic chemistry , physics , quantum mechanics
The Kaymont‐Rotronics Hygroskop DT, the Beckman‐Sina and the Protimeter were tested for their ability to measure water activity (a w ) of five foods over the 0.11 – 0.85 a w range. Each instrument was calibrated at 30 ± 0.1°C against ten saturated salt solutions using a modification of the AOAC Method 32.004‐32.009. Regression of the reading versus true a w , as determined by the vapor pressure manometer (VPM), gave high r 2 values for the saturated salt solutions between 0.32 – 0.85 a w . An error of approximately 0.01 a w units was found using the 1 hr data but no significantly better regression line was found using the 24‐hr data as compared to I hr data. Measurement of the a w of five foods, however, gave values differing by an average of 0.051 a w units as compared to the VPM readings. This study demonstrates justification of the FDA cutoff a w value of 0.85 for low‐acid foods as a margin of safety.