Abstract
Invertase ((beta-D-fructofuranoside fructohydrolase; EC 3.2.1.26) constitutes an improtant microbial enzyme with wide applications in differnt food and pharmaceutical sectors. The present work used the biotherapeutic yeast Saccharomyces boulardii to produce invertase under different aeration rates in stirred tank bioreatcr. Our results showed that an aeration rate of 1 v v(-1) m(-1) was the most suitable in terms of cell growth and invertase productivity. Highest enzyme production was recorded 14950 U L-1 after 50 h of cultivation. The production process was further optimized using different feeding strategties to overcome substrate limitation side effects encountered during batch cultivation. Sucrose feeding enhanced cell growth and enzyme productivity over batch cultivation by about 56.5% (from 7.35 to 11.5 g L-1) and 35.5% (from 14950 to 20250 U L-1), respectively. Furthermore, during feeding phase, invertase prodcution rate was improved by about 62.5% (from 299 to 486 U L-1 h(-1)), while growth rate remained constant. Additionally, the improved invertase production was mainly due to increased biomass and not cell productivity, since both batch and fed-batch cultivations have nearly similar specific growth values (2243.9 and 2194.1 U g(-1), respectively). On the other hand, feeding complete medium greatly enhanced process parameters. Cell growth and invertase production increased from the batch cultivation by about 143.8 and 120.1% (17.92 g L-1 and 32900 U L-1, respectively), and from the sucrose-feeding cultivation by about 55.8 and 62.5%, respectively.