Optimization of Invertase from Aspergillus niger Grown on Low Cost Agricultural Wastes by Response Surface Methodology (RSM)

Aim: To optimize media components and cultural conditions using response surface methodology (RSM) in the production of invertase by Aspergillus niger grown on potato peels (P1) and pineapple peels (P2).

Place and Duration of Study: The study was conducted at Environmental Microbiology laboratory, University of Port Harcourt, Choba between September 2015 and January 2017.

Methodology: Chemical analyses of P1 and P2 were carried out using standard methods. Invertase production was screened using Fehling solution test coupled with invertase activity assay. Reducing sugar was estimated using dinitrosalicylic acid (DNS) procedure. The RSM optimization design involved four (4) independent variables (pH, temperature, pineapple peels concentrations, and potatoes peels concentrations) at five (5) levels, screened through thirty (30) different experimental runs using central composite design (CCD).

Results: Optimal fermentation conditions that yielded maximum invertase (321.4 U/mL) and biomass (11.34 mg/mL) by A. niger was achieved with the combination of pH 9.0, temperature 35°C, pineapple peels concentration 10%, and potato peels concentration 50%. The model used gave a predicted R-Squared of -0.2258. Negative "Predicted R-squared” implies that the overall mean may be a better predictor of the response than the current model. "Adequate precision" of 6.190 was obtained, showing that the model can be used to navigate the design space.

Conclusion: This result has demonstrated the efficiency of RSM technique to optimize invertase production from A. niger using potato and pineapple peels as substrates. The use of local substrates can make invertase production economically attractive.