The present study showed that the texture firmness of banana pulp decreased gradually to the extent of nine fold from the raw stage to the ripe stage.
The ripening of banana fruit might be associated with the physical and biochemical changes of banana tissues. It has been reported that many carbohydrate hydrolases including xylanase
may contribute to fruit softening.
The specific activity of xylanase was highest at a texture
firmness of 210 cN. Samples at this level were then
used as a source for enzyme preparation.
The final step of enzyme purification from Sephadex G-50 gel
filtration resulted in a yield of 4.1% of the total activity, 0.28% retention of the total protein and a 14.7-fold increase in specific activity.
Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed a single band of protein, therefore, the enzyme was purified to homogeneity.
Most xylanases have been reported to have molecular weights ranging from about 20 kDa to 60 kDa.
Xylanase from the present work had an apparent molecular mass, estimated by SDS-PAGE and Sephadex G-50, of 19 kDa and 21 kDa, respectively.
The enzyme appears to be a monomeric protein having low molecular mass and less complex in size.
In general, xylanases from various microorganisms and plants are classified into two major families, F/10 and G/11.
Xylanase from Namwa banana fruit might be classified in the
family G/11 since xylanases in the family F/10 arelarger and more complex.
Furthermore, molecularmass of this enzyme is within the range detected for xylanases belonging to the family G/11.
However, more investigation and information are needed to ensure the family classification of this enzyme.
The enzyme showed relatively high activity under acidic condition and it could work actively in a broad pH range of between 5.0 - 6.0. The enzyme had optimum activity at temperatures of 45°C - 50°C.
At 60°C it still had about 80% activity relative to that at the optimum temperature.
In conclusion the enzyme had low molecular weight, the purification steps were simple and after column chromatography it is free of cellulase activity. This enzyme might potentially be useful
for pulp biobleaching since its small size can easily penetrate the fibre wall structure and alter, more efficiently, the pulp properties. Furthermore, due to the lack of cellulase activity, this xylanase will
not deteriorate the cellulose fibre strength of paper products.