Aims: It is recognized that laser printed paper are difficult to deink using conventional method. This had lead to the suggestion of enzymatic approach to overcome the problem encountered by commonly employed deinking techniques. The present study aimed to investigate 7 commercially available enzymes for their suitability use in deinking of laser printed paper. Methodology and results: 3 cellulases, hemicellulases, xylanase and 2 lipases were used in enzymatic deinking of laser-printed wastepaper. Cellulase A “Amano”3 (C), Hemicellulase (H) and lipase (L) were selected for used in deinking because they possess either highest activity or broad pH stability compared to others enzymes. Different combination of enzymes was carried out to evaluate their effectiveness in deinking process. CH enzymes sequence was determined to be the most effective sequence in toner removal with 1.90% of brightness increment. However, only 0.95% of brightness increment was gained by enzyme sequence L. Highest deinking efficiency obtained was not proportional to the highest total reducing sugar produced. Conclusion, significance and impact of study: Enzyme (cellulase and hemicellulase) can be used to de-ink laserprinted wastepaper, which are difficult to be deinked by conventional chemical deinking process. Thus, enzyme deinking has high possibility as alternative method to current chemical deinking process which is not environmental friendly.

Aims: A local fungal isolate, Aspergillus niger USM F4 produced high level of mannanase activity when cultivated in a shallow tray system (45 x 40 x 7 cm3) using palm kernel cake (PKC), an easily available cheap agricultural waste which are found abundantly in Malaysia. Methodology and Results: A range of 0.25 to 1.5 cm bed heights were investigated in tracking in the most suitable condition and maximum production of mannanase. The highest mannanase production of 918.68 U/g substrate was obtained on the fifth day of cultivation after using all the optimised cultural conditions that consisted of 400 g of PKC that equivalent to 0.50 cm of substrate thickness with the particle size of ≤ 0.5 mm, moisture content of 80% (w/w) with the addition of 2% (w/w) molasses as a carbon source and 4% (w/w) ammonium nitrate as a nitrogen source, inoculums size of 1x107 spores/ml, with once at every 24 h of mixing frequency and cultivation temperature at room temperature 30±2 °C. Conclusion, significance and impact of study: The results obtained from this study showed that a shallow tray system was suitable to be used for getting highest enzyme production in SSF. Besides using a bigger volume of substrate, the correct substrate bed height is also important.

Aims: This present study focused on purification of fungal β-mannanase produced by Aspergillus niger USM F4 and also physicochemical characterisation of the purified enzyme. Methodology and results: The purified β-mannanase with a molecular mass of ~47.4 kDa was demonstrated on SDSPAGE gel. The enzyme signified a purification degree of 4-fold, with final specific activity of 196.42 U/mg. It reached an optimum catalytic activity at pH 4.0 and 60 °C. The thermal stability of the enzyme was up to 70 °C and maintained the 50% activity after 30 min at 80 °C. Meanwhile, the pH stability was in the range of pH 3.0-9.0 and a 30 min half-life at pH 10.0. All chemical substances manifested an inhibitory effect on purified β-mannanase, with SDS (28.16 ± 0.05% residual activity) as the strongest inhibitor, followed by cupric ion (Cu2+) (49.51 ± 0.09% residual activity). As a whole, the enzyme displayed a substrate specificity in the order of locust bean gum (LBG) > carboxymethylcellulose > soluble starch > xylan from oat spelt > α-cellulose. Its preference for LBG has generated the Km and Vmax values of 0.20 mg/mL and 9.82 U/mL, respectively. Conclusion, significance and impact of study The outcomes of our study offer potential for use at industrial scales, particularly in the oligosaccharides production that involve acid-related activity, wide-ranging temperature and pH stability.
Aspergillus niger ; beta-Mannosidase