Optimized production and characterization of thermostable invertase from Aspergillus niger IBK1, using pineapple peel as alternate substrate

Production of thermostable invertase from Aspergillus niger IBK1 cultivated under submerged fermentation, using pineapple peel as a low-cost substrate, was investigated. Effects of some physical and nutritional factors such as pH, temperature, carbon sources and nitrogen sources on invertase production were studied. The enzyme was purified and characterized to evaluate its potentials for industrial applications. Maximum yield of invertase (24.20 +/- 0.38 U/mL) was at 120 h fermentation period at pH 5.0 and 35 degrees C. Sucrose, glutamic acid and peptone all enhanced enzyme production. The invertase was partially purified by sephadex G-100 gel filteration chromatography, after which a 34.57-fold increase in specific activity and a yield of 8.78% was achieved. Native molecular weight of the enzyme was 67.7 +/- 0.21 kDa using gel permeation chromatography on Sephadex G-100. The optimal pH and temperature of activity were 4.5 and 60 degrees C, respectively. The enzyme was highly stable at temperature 35-65 degrees C and at pH 3.0-6.0. K-m and V-max values for sucrose were 21.93 +/- 3.72 mM and 35.71 +/- 2.02 U/min/mL respectively. Na+, K+, Ca2+ and EDTA all enhanced the activity of A. niger IBK1 invertase while Mg2+ showed inhibitory effect. This study reveals invertase from A. niger IBK1 has potentials for industrial and biotechnological applications