초록
<P><B>Abstract</B></P> <P>Sequential optimization strategy was used to enhance the production of extracellular polygalacturonase by a newly isolated <I>Aspergillus fumigatus</I> R6 using rice bran as a substrate in solid state conditions. Three significant variables influencing the polygalacturonase production were identified as initial moisture level, temperature and incubation time (<I>P</I> <0.0001). The model established by face-centered central composite design was significant (<I>P</I> <0.05) with high R<SUP>2</SUP> (0.98). The model validity was verified and the optimum conditions were at an initial moisture level of 49.6%, 33°C and 129h of incubation time with the maximum polygalacturonase activity of 565U/g, resulted in 2.65 fold increase in polygalacturonase activity compare to the unoptimized conditions. Kenaf stem treated with <I>A. fumigatus</I> R6 polygalacturonase enzyme at 72h produced high strength of kenaf bast fibers (287MPa) with high Young’s modulus (10404MPa) and the color is in satisfactory.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Polygalacturonase production by <I>A. fumigatus</I> is affected by different factors. </LI> <LI> Maximum polygalacturonase activity could be predicted from regression model. </LI> <LI> Optimum cultural condition are 49.6% moisture, 33°C and 129h of incubation time. </LI> <LI> There is a 2.65 fold increment in polygalacturonase activity after optimization. </LI> <LI> Retting using polygalacturonase produced good-quality kenaf fiber. </LI> </UL> </P>