Production and characterization of laccase for enzymatic bleaching of sago starch from potential indigenous fungi

Herman Hadafi, Mohamad (2010) Production and characterization of laccase for enzymatic bleaching of sago starch from potential indigenous fungi. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

The potential use of extracellular laccase enzyme from fungal isolate on bleaching of sago starch was accessed. A total of 200 fungi isolates obtained from several different locations including sago processing mills and sago plantations were screened for laccase activities. The potential fungi Crinipellis roreri, a laccase enzyme producer was isolated from decayed sago pith obtained from Nitsei Sago Industries Sdn. Bhd., Mukah, Sarawak. The fungus was identified by Food Science Australia, a joint venture company between CSIRO and AFISC. Production of laccase was studied using shake-flask cUltur:) Highest laccase activity of crude enzyme exhibited by C. roreri was 519.5 U/mL when grown in Bhat and Wood medium with] % (w/v) soluble starch as carbon source and 1 % (w/v) com steep liquor as nitrogen source, incubated with 30 °C, pH 7.0 and agitated at 150 rpm. An incubation period of 120 hours gave optimum 'laccase activity. Fractionation of laccase activity was achieved with ammonium sulphate precipitation. Recovery of 30.7 and 59.4 % of laccase activity with purification factors of 6 and 10 were achieved with 20-40 and 40-60 % saturation, respectively. Further gel filtration chromatography of the dialyzed pooled enzyme fraction of20-6O % led to purification of laccase with specific activity of 3847.4 U/mg and molecular weight of 80 kDa. Optimum temperature and pH for purified laccase were pH 6.0 and 50 °C, respectively. The purified laccase obtained from C. roreri had the ability to bleach sago starch. An increased in the 'L' value of 8 units from 83 to 91 lightness index was achieved when 5 % (v/w) laccase with the activity of 519.5 U/mL was treated with sago starch for 3 hOUTS. The laccase enzyme from C. roreri also gave higher bleaching ability compared to commerciallaccase namely Pulpzyme® and Novozyme®. The increased in the 'L' value indicates the potential use of the laccase from C. rarer; for upgrading the Industrial Grade Starch (MS 468, 1976) ('L' value < 90) to Food Grade Starch (MS 470, 1992) ('L' i value> 90) according to the Malaysian Standard, by biological means.

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