Optimization of cultural conditions for polygalacturonase production by a newly isolated Aspergillus fumigatus R6 capable of retting kenaf

Abstract

Sequential optimization strategy was used to enhance the production of extracellular polygalacturonase by a newly isolated Aspergillus fumigatus 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 (P < 0.0001). The model established by face-centered central composite design was significant (P < 0.05) with high R2 (0.98). The model validity was verified and the optimum conditions were at an initial moisture level of 49.6%, 33 °C and 129 h of incubation time with the maximum polygalacturonase activity of 565 U/g, resulted in 2.65 fold increase in polygalacturonase activity compare to the unoptimized conditions. Kenaf stem treated with A. fumigatus R6 polygalacturonase enzyme at 72 h produced high strength of kenaf bast fibers (287 MPa) with high Young's modulus (10404 MPa) and the color is in satisfactory.

Pectinolytic enzymes-solid state fermentation, assay methods and applications in fruit juice industries: a review

“…Patil and Dayanand (2006), Hendges et al (2011), Demir and Tari (2014), Barman et al (2014) and Wong et al (2017) obtained the maximum polygalacturonase production by Aspergillus strains at 34, 30, 37, 32.37 and 33 °C, respectively. Jahan et al (2017) reported decrease in production by 29 and 32% when fermentation was carried out at 40 and 45 °C, respectively.…”

“…Most widely used Aspergillus sps. for polygalacturonase production are A. sojae (Heerd et al 2012;Demir and Tari 2014), A. niger (Dhillon et al 2007;Ruiz et al 2012;Darah et al 2013;Trentini et al 2015;Anand et al 2017;Mahmoodi et al 2017;Patidar et al 2017), A. fumigatus (Sandri et al 2015;Wong et al 2017), A. sydowii (Singh and Mandal 2012), A. tubingensis (Tai et al 2014;Patidar et al 2016), A. carbonarius (Nakkeeran et al 2011), A. niveus (Maller et al 2011), A. awamori (Botella et al 2005;Diaz et al 2012) and A. oryzae (Meneghel et al 2014;Biz et al 2016). In recent reports, bacterial isolates Bacillus subtilis SAV-21 (Kaur and Gupta 2017) and Bacillus licheniformisusin (Pervez et al 2017) have been reported to produce pectinase in SSF.…”

“…Rice husk, supplemented with (g/l) pectin, 10; sucrose, 20; K 2 HPO 4 , 1.0; NaNO 3 , 30; MgSO 4 •7H 2 O, 5.0; KCl, 10; FeSO 4 •7H 2 O, 0.01 and pH 4.0 has been used as solid carrier for the production of polygalacturonase (Tai et al 2014). Wong et al (2017) has reported utilization of rice bran as solid substrate for polygalacturonase production by newly isolated A. fumigatus R6.…”

“…Maximum production of pectic enzyme from different microorganisms varies mainly from 1 to 7 days (Table 4). Wong et al (2017) reported 129 h of incubation period for pectinase production in SSF by A. fumigatus. Demir and Tari (2014) showed increase in polygalacturonase production sharply by A. sojae after the second day of incubation period and maximum polygalacturonase production (136.9 U/gds) could be achieved on the 4th day of incubation using wheat bran as solid substrate.…”

“…Heerd et al (2014) also used 0.2 N HCl for maintaining the 160% moisture content of solid medium wheat bran and sugar beet pulp. Wong et al (2017) reported 49.6% moisture content maintained with mineral solution. Mahmoodi et al (2017) reported maximum polygalacturonase activity at 70% (w/w) of the initial moisture content.…”