Use of Nutshells Wastes in the Production of Lignocellulolytic Enzymes by White-Rot Fungi

Abstract

Agricultural wastes are an environmental and economic problem that countries must strive to solve as soon as possible. White-rot fungi can take advantage of these wastes through an efficient process involving the bioconversion of lignocellulosic materials. Therefore, this work has used pine needles (Pinus pseudostrobus) and nutshells (Carya illinoinensis), relevant wastes in Mexico, as substrates for growing three fungal strains (Ganoderma lucidum, Lentinula edodes, and Pleurotus ostreatus) on PDA plates supplemented with these materials. Besides, the capacity to produce lignocellulolytic enzymes by these three fungi through solid-state fermentation has been evaluated using pine needles and nutshells along with barley straw. The relevant results suggest that nutshells are a potential substrate for growing G. lucidum (mycelial growth rate of 0.758 cm d-1). Albeit pine needles waste has allowed G. lucidum growth (0.402 cm d-1), L. edodes and P. ostreatus growth on PDA supplemented plates were not observed. Further to this, nutshells or pine needles combined with barley straw were used as substrates through solid-state fermentation to produce lignocellulolytic enzymes (cellulase, xylanase, and laccase). G. lucidum presented the highest cellulase productivity (3.03 ± 0.34 IU/gdm·d) using nutshells and barley straw (BS_NS) as substrates, while it was half using pine needles and barley straw (BS_PN) (1.35 ± 0.20 IU/gdm·d). The results were similar for xylanase productivity because G. lucidum produced 4.80 ± 0.61 IU/gdm·d using BS_PN, slightly higher than the BS_NS (3.79 ± 0.29 IU/gdm·). Finally, nutshells might be a suitable substrate for the growth of white-rot fungi, mainly the G. lucidum strain, making it an ecological alternative for future biotechnological applications.