The potential of household food residues to substitute commonly used lignocellulosic substrates for the cultivation of oyster mushroom (Pleurotus ostreatus): Secretome response and bioconversion capacity

Household food residues (HFRs), a substantial yet underexplored fraction of lignocellulosic waste, were evaluated as potential substitutes for conventional substrates (wheat straw-WS and barley straw-BS) in the process of P. ostreatus basidiocarps cultivation. Prior to basidiocarps cultivation, the lignocellulosome was profiled during solid state fermentation of WS and BS supplemented with HFRs (almond seed coats, peanut shells, spent espresso grounds, spent immuno mix tea or spent milk thistle seeds). Laccases were dominant in the ligninosome, with a peak activity (9260.52 U/L) measured after fermentation of wheat straw mixed with spent espresso grounds. Xylanases were dominant in the P. ostreatus hemicellulosome, with activities exceeding 2000 U/L observed on several HFRs supplemented substrates. Although the highest delignification rates were recorded on pure WS and BS (about 70%), their substitution with spent espresso grounds slightly decreased delignification levels, while hemicellulose removal was increased by HFRs. Rapid substrate colonization and basidiocarps formation were observed on all tested substrates. The highest yields (169.95 g/kg and 156.91 g/kg) and biological efficiencies of cultivation (89.33% and 85.33%) were recorded on BS-based substrates. The structure of the spent substrates and obtained basidiocarps was characterized using Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). These results demonstrate the strong potential HFRs for conversion into P. ostreatus basidiocarps through sustainable and commercially relevant cultivation strategies.