Availability of Baker’s Yeast: A Survey of Propagation

Abstract

The potential of Rhizga (Plecthantrus esculentus) for the propagation of baker’s yeast in different starch sources
such as cassava (Utillisima esculentus), sweet potato (Ipomea batatas), rhizga (Plectanthrus esculentus) and
tacca (Tacca leontopetaloides) was investigated. This was done by an enzyme hydrolysis of the substrates using
alpha/beta amylases from Bacillus utilis, Termamyl (a commercial thermostable alpha amylase from Bacillus
licheniformis) and amyloglucosidase (a commercial preparation from NOVO). The hydrolysates were employed
as feedstock for the aerobic cultivation of Saccharomyces cerevisiae DSM2155. From the results, there was a
significant difference (p<0.05) between the hydrolysate yield (expressed as dextrose equivalent, DE) of the substrates.
Alpha and beta - amylases from Bacillus subtilis produced consistently lower yields of 25DE, 28DE,
89DE and 88DE for sweet potatoes, cassava, rhizga and tacca respectively as compared with the termamyl and
amyloglucosidase combination which resulted in higher hydrolysate yields of 82DE, 90DE, 100DE and 75DE
respectively. The results of the aerobic growth studies showed that the hydrolysates from all the substrates supported
the growth of Saccharomyces cerevisiae DSM 2155 with. biomass concentrations of 1.82x105cells/ml for
cassava, 4.86x104 cells/ml for sweet potatoes, 1.84x104 cells/ml for tacca and 1.4 x104 cells /ml for rhizga; while
molasses (used as control) yielded 3.0 x102 cells/ml after an incubation period of 72hrs.