Agro-industrial residues consist of various wastes from the agriculture and the food industry, which account for several thousand tonnes of waste per year. These wastes pollute the environment and represent a loss of biomass which can otherwise be processed to other value-added products through the activities of microorganisms. This study aims to ferment the seed cake of Jatropha curcas an agro-based waste, for the production of gibbererllic acid using Aspergillus niger (ATCC 16404) and Aspergillus terreus (ATCC 20542) in submerged fermentation. The seeds of Jatropha were cracked, ground and defatted. The ground seeds were pretreated with 0.5% tetraoxosulphate VI acid (w/v), and fermented separately in a modified Czapek Dox broth using the test organisms. Carboxyl methylcellulose (CMC) was used as control. The fermentation conditions were: pH 5.3; substrate concentration (1.5g); inocula size 2 mL; (1.2 x 107 spores/mL A. niger) (5.83 x 106 spores/mL A. terreus); temperature 25oC; fermentation period of 7 days. Gibberellic acid yield of 13.8±0.97 g/L and 12.2±0.97 g/L was produced by A. niger and A. terreus respectively. The yield from the CMC substrate was 5.60±0.49 and 2.0±0.32 g/L from A. niger and A. terreus respectively. The fermentation parameters were then varied in order to optimize the yield of the acid. The highest yield of gibberellic acid was 31.0±0.23 g/L and 32.8±0.25 g/L at pH 5, substrate concentration 1.5g, inocula size 2 mL for 8 days; and pH 7, substrate concentration 3.5g and inocula size 2 mL for 8 days with A. niger and A. terreus respectively, representing a 55% and 63% yield increase by A. niger and A. terreus respectively. These results support the potential use of Jatropha seed cake for gibberellic acid production.
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