초록
<P><B>Highlights</B></P><P>► Ability of encapsulated yeast to produce ethanol at high temperatures was studied. ► S. cerevisiae was encapsulated in liquid core capsules of alginate and chitosan. ► Heat tolerance was investigated by consecutive batch and continuous cultures. ► Encapsulation increased the tolerance to elevated temperatures. ► Encapsulated yeast could persist temperatures as high as 42°C for a few days.</P> <P><B>Abstract</B></P><P>The ability of macroencapsulated <I>Saccharomyces cerevisiae</I> CBS 8066 to produce ethanol at elevated temperatures was investigated in consecutive batch and continuous cultures. Prior to cultivation yeast was confined inside alginate–chitosan capsules composed of an outer semi-permeable membrane and an inner liquid core. The encapsulated yeast could successfully ferment 30g/L glucose and produce ethanol at a high yield in five consecutive batches of 12h duration at 42°C, while freely suspended yeast was completely inactive already in the third batch. A high ethanol production was observed also through the first 48h at 40°C during continuous cultivation at <I>D</I>=0.2h<SUP>−1</SUP> when using encapsulated cells. The ethanol production slowly decreased in the following days at 40°C. The ethanol production was also measured in a continuous cultivation in which the temperature was periodically increased to 42–45°C and lowered to 37°C again in periods of 12h. Our investigation shows that a non-thermotolerant yeast strain improved its heat tolerance upon encapsulation, and could produce ethanol at temperatures as high as 45°C for a short time. The possibility of performing fermentations at higher temperatures would greatly improve the enzymatic hydrolysis in simultaneous saccharification and fermentation (SSF) processes and thereby make the bioethanol production process more economically feasible.</P>