Exploring the lignolytic potential of a new laccase producing strain Kocuria sp. PBS-1 and its application in bamboo pulp bleaching

Abstract

The pulp and paper industry is one of the largest polluting industries in the world employing chlorine-based bleaching processes. The hazardous impact on the environment can be mitigated by either removal of chlorine or minimizing its use by developing alternative bleaching methods. This study was undertaken to explore the applicability of a new laccase isolated from Kocuria sp. PBS-1 for bamboo pulp bleaching. The enzyme was optimally active at 50 °C and pH 7 and the Km, Vmax and Kcat were 39.45 ± 5.47 mM, 407.40 ± 4.9 μmol min−1 and 124.5 s−1 respectively. Further, the t1/2 was found to be 13 h at 30 °C. This laccase produced a significant increase in the ISO brightness to 80.03 ± 1.68% after LMPZ (Laccase, Mediator, Peroxide and Ozone) bleaching. A significant reduction in the kappa number was recorded for L, LM, LMP and LMPZ treated pulp samples. The FTIR peak at ~1118 cm−1 attributed to lignin present in spectra of the control pulp sample was not observed in spectra of the treated pulps. A new band at 1162 cm−1 in treated pulps indicated degradation of syringyl groups along with an increase in the total crystallinity index, empirical crystallinity index and apparent crystallite size of the cellulose. XRD data of treated pulp samples revealed an increase in the cellulose crystallinity index as per A1430/897 ratio. The SEM of treated pulps showed a change in morphology of pulps like the appearance of cracks, crevices, grooves and peeling of fibrils due to lignolytic activity. These findings may provide leads for the development of new cleaner and alternative methods for pulp bleaching.