Effect of edible oils and Cu (II) on the biodegradation of rice by-products by Ganoderma lucidum mushroom Pablo Daniel Postemsky 1 , Silvia Elena Delmastro 1 , Néstor Raúl Curvetto * Laboratory of Biotechnology of Edible and Medicinal Mushrooms, CERZOS (CONICET-UNS), Camino de La Carrindaga Km7, Bahía Blanca 8000, Buenos Aires, Argentina article info Article history: Received 11 March 2014 Received in revised form 5 May 2014 Accepted 5 May 2014 Available online Keywords: Reishi Rice straw Rice husks Solid-state fermentation White-rot fungi abstract The biodegradation of rice agro-industrial residues (straw and husks) to obtain the medicinal white-rot fungi Ganoderma lucidum and a crude extract of laccases as by- product was studied. Mycelium growth analysis on substrate formulations in a solid state fermentation system showed a good growth perfor- mance on substrates containing 57e69% straw, 25e30% husk, 5e10% rice bran, and 0e1% olive oil. Total mushroom production of dried mushrooms increased from 2.9% to 3.7% when using 5% vs. 8% mycelium inoculation rates, and from 3.6% to 4.1% when 1% olive oil was added to the substrate formulation. Addition of 100 ppm Cu (II) as a substrate supplement increased laccase activity in mushroom residual substrate from 150 to 267 U/Kg substrate and produced a three-fold increase in mushroom copper content. Extracted laccase activity was stable after four months in freezer storage (18  C) and after 16 freezing/thawing cycles. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Biodegradation of lignocelullosic wastes by white rot fungi is an energy-efficient process to produce edible and medicinal mush- rooms while reducing the environmental impact which would otherwise be originated by an inadequate disposal. Ganoderma lucidum (Curtis: Fr.) P. Karst. (Reishi), a Basidiomycete of the family Ganodermataceae, is a medicinal mushroom with a broad spectrum of health benefits. The bioactive components found in this mush- room have numerous health properties to treat diseased conditions such as hepatopathy, nephritis, hypertension, hyperlipidemia, arthritis, neurasthenia, insomnia, bronchitis, asthma, gastric ulcers, atherosclerosis, leukopenia, diabetes, anorexia, and cancer (Batra et al., 2013). Ganoderma lucidum is a white rot fungus usually grown on substrates made of a variety of crop and agro-industrial residues (González Matute et al., 2002, 2011). It uses three important en- zymes, namely, laccase, (EC 1.10.3.2), lignin peroxidase (EC 1.11.1.14) and manganese peroxidase (EC 1.11.1.13) (Manavalan et al., 2012) to degrade lignin. Rice straw, husks and rice bran are some of the most abundant agro-industrial by-products in the world. Some uses of rice straw and husks include forage and thermaleenergy production; how- ever these residues are mostly disposed of by burning them in open fields in a clearly non environmentally friendly practice (Lim et al., 2012). Other bioprocesses to treat rice by-products, like biofuel production, are under development. The great challenge in this field is to overcome the silica and lignin barrier to gain access to the carbohydrates (Zhang et al., 2012). In this sense, fungi have a tolerance to silica and some of them have the enzyme system required to degrade the lignin barrier. Moreover, some specialty mushrooms have been studied with the aim of recycling them into food as is the case of Volvariella volvacea (Kumhomkul and Panich- pat, 2013) and Pleurotus spp. (Iqbal et al., 2005; Frimpong-Manso et al., 2011). Degradation of these rice by-products by other economically important species like Lentinus edodes has not been studied extensively (Ashrafuzzaman et al., 2009), nor has it been evaluated using G. lucidum. In nature, G. lucidum grows as a parasite or a saprotroph on a wide variety of trees. Thus, it is expected that its mycelium should be able to cause a satisfactory degradation of a rice-based substrate, and if so, the process could eventually be improved by the addition of supplements or additives to overcome possible nutrient de- ficiencies as it occurred in the case of the bioconversion of spent Abbreviations: B/A, biomass per area; BE, biological efficiency; SSF, solid-state fermentation; TMP, total mushroom production. * Corresponding author. Tel.: þ54 0291 4861666; fax: þ54 0291 4862882. E-mail addresses: pablop@criba.edu.ar (P.D. Postemsky), micouns@criba.edu.ar (S.E. Delmastro), ficurvet@criba.edu.ar, micouns@criba.edu.ar (N.R. Curvetto). 1 Tel.: þ54 0291 4861666; fax: þ54 0291 4862882. Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod http://dx.doi.org/10.1016/j.ibiod.2014.05.006 0964-8305/Ó 2014 Elsevier Ltd. All rights reserved. International Biodeterioration & Biodegradation 93 (2014) 25e32