Glass transition temperatures and fermentative activity of heat-treated commercial active dry yeasts

Differential scanning calorimetry thermograms of various samples of commerc ial instant active dry yeasts revealed a clear glass transition typical of amorphous carbohydrates and sugars. The resulting glass transition temperat ures were found to decrease with increasing moisture content. The observed glass curve was similar to that of pure trehalose, which is known to accumu late in large amounts in baker's yeast. The effect of heat treatment at var ious temperatures on the fermentative activity (as measured by the metaboli c production of CO2) of dry yeast was studied. First-order plots were obtai ned representing the loss of fermentative activity as a function of heating time at the various temperatures assayed. Significant losses of fermentati ve activity were observed in vitrified yeast samples. The dependence of rat e constants with temperature was found to follow Arrhenius behavior. The re lationship between the loss of fermentative activity and glass transition w as not verified, and the glass transition was not reflected on the temperat ure dependence of fermentative activity loss.