A differential scanning calorimeter equipped with liquid nitrogen cooling accessories
was used. In order to avoid condensation of water, dry nitrogen
gas was used to purge the surroundings of the furnace and the
furnace chamber at 200 and 80 ml/min, respectively. Powder
samples (5–10 mg) were weighed into a 40-μl aluminium
standard crucible and hermetically sealed with an aluminium
standard lid (ME-51119871, Mettler-Toledo). All samples
were cooled at a rate of 20 °C/min to reach a temperature that
was about 60 °C below their Tg midpoints. Then, the samples
were reheated at 10 °C/min to a temperature about 40 °C above
Tg midpoints to analyse the glass transition temperature. Glass
transition temperature (Tg) was analysed using the STARe
software (version 8.01, Mettler-Toledo). Soy sauce powders
were equilibrated at different RHs before the analysis, as
mentioned in “Moisture Adsorption Analysis”. The midpoint
of glass transition was considered as the characteristic temperature
of the transition. All Tg were the means of at least two
independent scans.