Measurement of Water Activity of Salt Solutions and Foods by Several Electronic Methods as Compared to Direct Vapor Pressure Measurement

J. A. STAMP, S. LINSCOTT, C. LOMAURO, T. P. LABUZA

Research output: Contribution to journalArticlepeer-review

38 Scopus citations

Abstract

The Kaymont‐Rotronics Hygroskop DT, the Beckman‐Sina and the Protimeter were tested for their ability to measure water activity (aw) of five foods over the 0.11 – 0.85 aw 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 aw, as determined by the vapor pressure manometer (VPM), gave high r2 values for the saturated salt solutions between 0.32 – 0.85 aw. An error of approximately 0.01 aw 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 aw of five foods, however, gave values differing by an average of 0.051 aw units as compared to the VPM readings. This study demonstrates justification of the FDA cutoff aw value of 0.85 for low‐acid foods as a margin of safety.

Original languageEnglish (US)
Pages (from-to)1139-1142
Number of pages4
JournalJournal of food science
Volume49
Issue number4
DOIs
StatePublished - Jul 1984

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