How Coffee and Mushroom Waste Can Feed Our Plates?

A research team turned agricultural and industrial leftovers into perfect beds for growing the mushroom Pleurotus columbinus, prized for its delicate aroma and nutritional benefits. They blended spent mushroom substrate (SMS), espresso coffee grounds (SCG), faba bean residues (FBR), pistachio shells (PS) and wheat straw (WS), adjusting ratios and optionally adding wheat bran and soybean flour. The fastest mycelial growth (7.6 mm per day) occurred with a 70 % SMS‑30 % FBR mix without supplements. Substrates containing SCG yielded the highest biomass, up to 800 mg per gram of dry weight. Combining SMS with PS or SCG shortened incubation times, speeding up fruiting body emergence. During colonisation, carbon content dropped while nitrogen rose, showing efficient nutrient uptake. Laccase activity peaked near 60 000 U g⁻¹ on 70 % SMS‑30 % FBR and 80 % SMS blends, whereas pistachio shells boosted total cellulase activity. All mixes produced more carbohydrates than the control, and the SMS‑SCG or SMS‑WS combinations achieved the highest biological efficiency (59‑87 %) and intracellular polysaccharide levels of 35‑46 % by weight. These findings prove that agro‑industrial waste can become valuable resources for cultivating mushrooms rich in bioactive compounds, cutting waste and supporting a circular economy.

Pleurotus columbinus is a biotrophic fungus capable of degrading lignocellulose thanks to a suite of extracellular enzymes. Among them, laccase (EC 1.10.3.2) oxidizes phenolic compounds, facilitating lignin breakdown, while cellulases (EC 3.2.1.4) hydrolyze cellulose chains, releasing glucose for mycelial growth. In the tested substrates, the carbon‑nitrogen (C/N) ratio varied widely; lower C/N values (around 15‑20) promoted rapid nitrogen assimilation, a crucial element for protein synthesis and enzyme production. The observed nitrogen increase in colonized substrates indicates that the mycelium efficiently absorbs nitrogen from coffee grounds and faba bean residues, enhancing biomass yield. Intracellular polysaccharide (ICP) production is tightly linked to glucose metabolism derived from cellulase activity; ICP levels between 35 % and 46 % suggest a strong capacity to accumulate glucans, known for immunostimulatory properties. Moreover, residual phenolic compounds in pistachio shells can trigger oxidative stress responses in the fungus, stimulating laccase synthesis and natural antioxidant production. From a sustainability perspective, using waste streams such as SMS, SCG, PS and FBR reduces reliance on commercial sawdust‑based substrates, lowering production costs and carbon footprint. Biological efficiency (BE) exceeding 80 % in some blends demonstrates that converting waste into fungal biomass is highly effective, paving the way for circular agriculture systems where agro‑industrial by‑products become raw materials for functional food and pharmaceutical ingredients.