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

CAROLINA SCHEBOR; MIGUEL GALVAGNO; MARÍA DEL PILAR BUERA; JORGE CHIRIFE

BIOTECHNOLOGY PROGRESS

Wiley InterScience

Año: 2000 vol. 16 p. 163 - 168

8756-7938

Differential scanning calorimetry thermograms of various samples of commercialinstant active dry yeasts revealed a clear glass transition typical of amorphouscarbohydrates and sugars. The resulting glass transition temperatures were found todecrease with increasing moisture content. The observed glass curve was similar tothat of pure trehalose, which is known to accumulate in large amounts in baker’syeast. The effect of heat treatment at various temperatures on the fermentative activity(as measured by the metabolic production of CO2) of dry yeast was studied. Firstorderplots were obtained representing the loss of fermentative activity as a functionof heating time at the various temperatures assayed. Significant losses of fermentativeactivity were observed in vitrified yeast samples. The dependence of rate constantswith temperature was found to follow Arrhenius behavior. The relationship betweenthe loss of fermentative activity and glass transition was not verified, and the glasstransition was not reflected on the temperature dependence of fermentative activityloss.