Extraction of protease from starfruit (Averrhoa carambola L.) / Ezzana Zuraini Zainuddin

Proteases were extracted from starfruit of different maturity index of Index 2 (light green) and Index 7 (orange). The extracted proteases were purified using acetone and 40% ammo-nium sulphate. The enzyme activity of the obtained proteases were analysed for stability at different pH, temperature and during storage at 4°C. Molecular weight distribution of purified proteases were also determined with SDS-PAGE electrophoresis. Protein content of starfruit is 0.73%. Protein concentration of purified protease with 40% ammonium sulphate was higher compared to the acetone purification. Index 2 protease purified with a 40% ammonium sulphate have high enzyme activity at pH 8 and temperature 60°C while for Index 7 at pH 6 and 60°C. Index 2 protease purified with acetone have high enzyme activity at pH 8 and at 50°C while for Index 7 at pH 6 and 50°C. The enzyme activity of both maturity index of protease purified with acetone and 40% ammonium sulphate decreased with storage time. Starfruit protease had high enzyme activity in the range of 100 to 1100 CDU/mg. The protein band at 50 kDa was found in all the prepared proteases. Protein bands were clear for protease purified with acetone compared to the proteases purified with 40% ammonium sulfate. This study suggested that acetone precipitation is a better method to purify starfruit protease and protease content and activity are higher in starfruit at the unripe stage which is Index 2. Starfruit proteases may be used as a protein hydrolysing agent in several areas in food industries.