Thermal Properties of Aqueous Acetic Acid Solutions and Aged Vinegars at Low Temperature (Studies on Aged Vinegars and Their Physicochemical Characteristics. Part III)

Abstract

During long periods of storage, the acetic acid concentration of vinegar vapor decreases, and the odor and taste mellow. Our previous paper on NMR spectra demonstrated the formation of a stable molecular cluster with restricted migration of acetic acid molecules and decreased monomeric acetic acid which produced a harsh stimulative taste. In the study here, differential scanning calorimetry (DSC) was used to examine aqueous acetic acid solutions (acetic acid conc. 0~59%) and aged vinegars. Ice and eutectic mixtures were formed by lowering their temperature by 10°C/min. At the melting point, the DSC thermogram showed two peaks (peak 1 and peak 2). Peak 1 occurred at the -25 to 0°C region and was concerned with the fusion heat of ice and dissolution of water into aqueous acetic acid solution. Peak 2 occurring at -25°C was concerned with the fusion heat of the eutectic mixture. The fusion heat of all eutectic mixtures formed from solutions of acetic acid concentration below the eutectic composition (59%) was greater compared with that of eutectic solid from eutectic liquid. The heat of fusion of eutectic mixtures formed from aged vinegars decreased in proportion to the length of storage, i. e. the eutectic mixture of aged vinegars melted under lower heat compared with new vinegars. These findings suggest a specific liquid state occurred in aged vinegars, i. e. formation of a stable molecular cluster which can be transferred to a eutectic solid by liberating less heat energy. (Received April 19, 1984). © 1984, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.