Abstract

The thermotolerant yeast strain Kluyveromyces marxianus IMB3 was immobilized in calcium alginate and this was used in batch-fed reactor systems to convert lactose (4 g/l) to ethanol. Production of ethanol by the free and immobilized biocatalyst in the presence and absence of Mn2+ was compared. In systems containing the free microorganism in the presence and absence of Mn2+, ethanol increased to a maxi mum of 8 g/l within 40 hours with no significant difference in production by both systems. Ethanol production by the immobilized system in the absence of Mn2+ increased to a maximum of 13 g/l within 40 hours and then decreased to 9 g/l within 80 hours. Ethanol production by the immobilized system in the presence of Mn2+ increased to 14 g/l within 60 hours and this decreased to 13 g/l at 80 hours. When all systems were re-fed at 80 hours, ethanol production by systems containing the free biocatalyst increased to a maximum of 3 g/l while the immobilized system in the presence of Mn2+ increased to a maximum of 12 g/l. Subsequent experiments involving re-feeding the system at shorter time intervals demonstrated that ethanol production by the immobilized system on lactose-containing media at 45 degrees C was far superior to ethanol production by the free biocatalyst.