Carposome productivity of Pleurotus ostreatus and Pleurotus eryngii growing on agro-industrial residues enriched with nitrogen, calcium salts and oils

The suitability of the abundant agro-industrial residues wheat straw (WS; control), barley and oats straw (BOS) and rice husk (RH), supplemented with various sources of oils (sunflower, corn oil), nitrogen (peptone, yeast extract) and calcium salts (CaSO4·2H2O, CaCl2), as novel substrates in solid-state fermentation of selected Pleurotus ostreatus and P. eryngii mushrooms was investigated. The possible effect of different additives on mycelial growth rate, biomass production and endoglucanase, laccase and lipase biosynthesis were evaluated. Moreover, their impact on essential cultivation aspects (earliness, total mushroom yield, biological efficiency) and carposome quality parameters (weight, morphological characteristics) was assessed. Both fungi showed their highest growth rates on BOS substrates and the most positive implementation was CaSO4·2H2O 6 % w/w (Kr = 9.58 mm/ day; P. ostreatus, Kr = 9.42 mm/ day; P. eryngii), while different additives led to enhancement of biomass production. Pleurotus species demonstrated minimal levels of endoglucanase activity, with values ranging from 0.01 to 0.42 U/g of dry weight, regardless of the substrate and the stage of colonization. On the contrary, the maximum values of laccase activity were observed at 50 % of colonization on BOS and RH, while supplementation with nitrogen and calcium sources positively affected its biosynthesis. P. ostreatus and P. eryngii cultivated on BOS supplemented with peptone at 2 and 5 % w/w, synthesized significant laccase amounts, i.e., 12,165.78 and 8,624.55 U/g d.w., respectively. Satisfactory amounts of lipase were produced, especially in substrates supplemented with sunflower 2 % w/w, in quantities up to 1.42 U/g d.w., whereas the highest lipase activity was achieved by P. eryngii on WS supplemented with corn oil at 2 % w/w, with a value of 4.25 U/g d.w. being recorded. Regarding fermentation of Pleurotus species in polypropylene bags, WS and BOS supported faster colonization and shorter earliness period than RH substrates, whereas supplementation did not seem to affect these culture parameters. Furthermore, oils supplementation had a positive effect on BE of both species, with values up to 100 % for P. ostreatus and 80 % for P. eryngii on WS and BOS, whereas on RH the lowest BE values were detected. Morphological characteristics were not significantly affected by the additives. Results indicate the positive impact that certain additives have on mushroom productivity and production of enzymes with great financial and environmental importance.