## 4 Materials and Methods
### Solid-State Fermentations  
Prior to fermentation, each substrate was thawed and sterilised by autoclaving at 121 \({}^{\circ}\)C for 20 min. _A. niger_, _A. oryzae_ and _P. canemberti_ were sporulated on Sabouraud dextrose agar (SDA) medium (Merck KGaA, Darmstadt, Germany). _P. cinnharitins_ was propagated on potato dextrose agar (PDA) medium (Merck KGaA, Darmstadt, Germany) and a preinoculum (myceliated grains) was obtained on sterilised rice cultured at 25 \({}^{\circ}\)C until complete colonisation. Five 500 mL Erlenmeyer flasks containing 50 g of sterile substrate without adjusting their moisture content and substrate pH were inoculated with spore suspension (3 mL 10\({}^{7}\) spores/mL in 0.9% saline solution) or myeliliated rice preinoculum (5 g wet weight). The flasks were then incubated at 25 \({}^{\circ}\)C (_P. cinnharitins_ and _P. camenberti_) or 28 \({}^{\circ}\)C (_A. niger_ and _A. oryzae_) in the dark until more than 90% substrate colonisation was reached through visual inspection. Each substrate/fungus combination and corresponding sterile, negative controls were incubated in parallel. Fermentations were visually assessed daily to determine the fermentation end point through substrate colonisation. All substrateswere >90% surface covered by mycelia 10 days post-inoculation with the exception of five fermentations: _Aspergillus niger_ on red grape marc; _Penicillium camenberti_ on olive cake and red grape marc; and _Pycnorporus cinnabarinus_, on spent brewer's grain, and red grape marc. After fermentation, samples were stored at \(-20\)\({}^{\circ}\)C in glass vials flushed with nitrogen pending volatiles analysis.  
Headspace Solid-Phase Microextraction (HS-SPME) Coupled to Gas Chromatography-Mass Spectrometry (GC-MS)  
Solid-state fermentation samples were thawed overnight at 4 \({}^{\circ}\)C, weighed into 20 mLamber SPME headspace vials (2 g wet weight) and immediately fitted with a silicone/PTFE septum cap (Supelco). All extractions were carried out using a 1 cm 50/30 \(\upmu\)m DVB/CAR/PDMS (Supelco) fibre. Preincubation (10 min at 60 \({}^{\circ}\)C) was immediately followed by extraction (10 min). Desorption in the GC was performed under splitless mode (1 min at 250 \({}^{\circ}\)C). Then, the fibre was cleaned (5 min at 250 \({}^{\circ}\)C) in preparation for the next sample.  
Volatile compounds adsorbed into the SPME fibre were analysed by GC-MS by desorbing them into a Shimadzu QP2010 Plus GC-MS system via a CTC analytics Combi PAL autosampler. A fused silica HP-5 MS column (30 m \(\times\) 250 \(\upmu\)m \(\times\) 0.25 \(\upmu\)m) from Agilent was used to separate the analytes. The inlet temperature was fixed at 250 \({}^{\circ}\)C. The column flow rate was kept constant at 1 mL/min using ultra-high-purity-grade helium gas. The initial GC oven temperature was set at 35 \({}^{\circ}\)C, then immediately increased to 80 \({}^{\circ}\)C at a rate of 10 \({}^{\circ}\)C/min upon sample injection. Then, ramped again to 160 \({}^{\circ}\)C at a rate of 2 \({}^{\circ}\)C/min, followed by a final ramp at 10 \({}^{\circ}\)C/min to 260 \({}^{\circ}\)C. The GC-MS interface temperature was held at 250 \({}^{\circ}\)C, the ion source at 200 \({}^{\circ}\)C, and quadrupole at 200 \({}^{\circ}\)C. The ion source was operated in electron impact ionisation mode at 70 eV. Compounds were detected using mass spectra acquired in scan mode in the range of 33 to 400 \(m/z\).