INFLUENCE OF INOCULUM SIZE ON PHYTASE PRODUCTION AND GROWTH IN SOLIDSTATE FERMENTATION BY ASPERGILLUS NIGER

Abstract

Solidstate fermentation is experiencing renewed interest for industrial enzyme production. Previous studies onthe effects of fungal inoculum size on product yield have focused on spore inoculum. However, some organisms requirevegetative inocula. This study investigated the effects of initial inoculum colony age, vegetative inoculum size, and durationof fermentation on the production of fungal biomass and phytase in solidstate fermentation using Aspergillus niger grownon wheat bran and soy meal. Initial inocula from 7 and 14dayold potato dextrose agar (PDA) plates were used to studythe effect of inoculum colony age in liquid culture and its further influence on fermentation. The liquid inoculum size of (60 480 mg of biomass/5 g substrate) and the duration of fermentation were studied for 10 days with periodic sampling every48 hours. The study was conducted as a replicated full factorial experiment. Statistical analysis showed that phytaseproduction and growth were not affected by inoculum size (over 60 mg/5 g substrate) after 48 hours of fermentation. Theduration of fermentation was highly significant with a maximal phytase (1001
94 U/g substrate) and biomass (0.032
0.007g glucosamine/g substrate) formation at 192 h of SSF. Phytase yield and biomass formation were strongly correlated for the7 and 14day plate cultures (the estimated correlation coefficients being 0.87 and 0.73), indicating that phytase productionis strongly growthassociated.