Formulation of substrate from paddy straw and oil palm frond for cultivation of different mushroom species and its effect towards physical and selected biochemical properties

In Malaysia, rubber sawdust is the main substrate for cultivation of oyster mushroom. However, in recent years, the supply of rubber sawdust is dwindling due to its high demand in other sectors, including poultry, furniture, fuel, and construction. Thus, this study aims to establish a new substrate formulation from available agri-biomass of paddy straw and oil palm frond by cultivating three popular mushroom species in Malaysia. In this study, grey oyster mushrooms (Pleurotus ostreatus) (GM), white oyster mushrooms (Pleurotus florida) (WM), and split gill mushroom (Schizophyllum commune) (SM) were cultivated on sawdust (T1, control as commercial substrate), paddy straw (T2), and oil palm frond (T3) formulated substrates. The objectives of this study are to analyse the carbon (C)/ nitrogen (N) ratio, minerals (copper [Cu], iron [Fe]), and heavy metals content (zinc [Zn], lead [Pb], arsenic [As]) in the raw materials of the three substrates and their effects on physical and biochemical responses in the cultivated mushroom species. The physical response in terms of growth of the cultivated mushroom species was analysed based on mycelial development, first primordial, pileus diameter, total yield, and biological efficiency. Meanwhile, the selected biochemical responses were analysed on the minerals, heavy metal content, β-glucan content, and total dietary fibre (TDF) in the cultivated mushroom species. The result of C/N ratio of the T1 and T3 substrates (196.17 and 162.32) was significantly high compared to T2 (59.02). While, T3 showed good performance on mushroom physical growth. The mineral content in T3 recorded the highest for Cu (88.00 ± 2.00 mg/kg) and Fe (433.33 ± 3.06 mg/kg), while for heavy metal content, T1 recorded the significant highest (p<0.05) of Zn (105.33 ± 1.15 mg/kg) and Pb (21.33 ± 5.03 mg/kg) and T2 recorded the significant highest (p<0.05) of As 6.04 ± 0.26 mg/kg. The physical growth in mushrooms on T3 gave a significant short (p<0.05) duration for the mycelium colonisation on the substrate and early first primordial formation for GM (22.00 ± 0.00 days and 25.33 ± 2.52 days), WM (22.33 ± 0.58 days and 25.33 ± 0.58 days) and SM (18.00 ± 0.00 days and 22.00 ± 0.00 days). Among the three substrates, T3 yielded the significant highest pileus diameter for GM (12.57 ± 2.83 cm) and the significant highest total yield for WM (148.06 ± 0.90 g in four cycles). The biochemical properties in all three mushroom fruit bodies in the three cultivated substrates showed low accumulation of heavy metals from the substrates, mostly reaching the safe limit by Food and Agriculture Organisation except for Zn in T1 (ranged 66.20 – 146.20 mg/kg) and As in T2 (ranged 0.36 – 2.32 mg/kg. The bioaccumulation factor, Ka for most of the three mushroom species was in the descending order of Fe > Cu > Zn > As > Pb. Meanwhile, As and Pb were accumulated at minimal levels. In this study, the highest β- glucan content was observed in oven-dried SM cultivated on T3 (54.20 ± 2.44%) compared to freeze-dried. T3 substrate also recorded the highest β-glucan content at the fourth flushed in GM (50.51 ± 4.38%), followed by the fourth flushed of WM (44.26 ± 0.10%) and first flushed in SM (50.17 ± 0.24%). SM cultivated on the T3 substrate recorded the highest TDF (56.10 ± 0.89 g/100g). In conclusion, the formulation of T3 (oil palm frond) showed the potential as a good substrate for mushroom cultivation on a commercial scale.