The global mushroom industry has experienced tremendous growth over the last two decades, with the white button mushroom (Agaricus bisporus) being the most widely cultivated species worldwide. However, this growth comes with environmental challenges, particularly the reliance on peat as a casing material.

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Peat, a non-renewable resource, is extracted from wetlands, leading to habitat destruction and significant carbon emissions. A recent study published in Biomass Conversion and Biorefinery (2025) offers a groundbreaking solution by introducing olive press cake (OPC)—a byproduct of olive oil production as a sustainable alternative to peat.

The Environmental Impact of Peat and the Need for Alternatives
Peat has been the preferred casing material in mushroom farming for decades due to its ability to retain water and provide a stable environment for fungal growth. However, peat extraction is highly destructive. Wetlands, which store vast amounts of carbon, are drained and dug up to harvest peat, releasing carbon dioxide into the atmosphere and destroying ecosystems.

With global mushroom production reaching 48 million tons in 2022, the industry’s dependence on peat is unsustainable. Researchers have explored alternatives like coconut fiber, composted bark, and spent mushroom substrate, but none have matched peat’s performance—until the discovery of olive press cake (OPC).

A Waste Product Turned Resource

The olive oil industry generates approximately 40 million tons of waste annually, including olive press cake (OPC), which consists of olive skins, pulp, and stones.

Traditionally, OPC is discarded through environmentally harmful methods like open burning, landfilling, or dumping into water bodies, leading to soil and water pollution.

OPC Enhances Yield and Nutritional Value

The study revealed significant improvements in both mushroom production and quality when OPC was incorporated into the casing layer.

Increased Mushroom Yields

The 3:1 peat-to-OPC ratio (P3:OPC1) produced the highest yield of 334.2 grams of mushrooms per kilogram of compost, surpassing the peat-only control, which yielded 238.8 grams per kilogram.

Even the 2:1 (P2:OPC1) and 4:1 (P4:OPC1) ratios outperformed peat, with yields of 289.4 g/kg and 310.2 g/kg, respectively. However, the 1:1 ratio (P1:OPC1) resulted in the lowest yield (217.7 g/kg), likely due to the high phenolic content in OPC, which can inhibit fungal growth at higher concentrations.

This finding highlights the importance of balancing OPC’s benefits with its potential drawbacks. The 3:1 ratio provides enough nutrients from OPC to boost growth while avoiding the negative effects of excessive phenolic compounds.

Improved Nutritional Profile

Mushrooms grown with OPC-enriched casing showed notable improvements in nutritional content. For example, the 1:1 peat-to-OPC formulation (P1:OPC1) produced mushrooms with 29.33% protein, compared to 26.86% in the control group.

Similarly, crude fat content increased to 2.44% (vs. 1.96% in peat-grown mushrooms), and ash content—a measure of mineral density—rose to 13.57% (vs. 11.60%). These enhancements are attributed to OPC’s rich nutrient profile, including nitrogen, organic matter, and bioactive compounds.

Mineral Enrichment in Mushrooms

OPC also significantly boosted the mineral content of mushrooms. Potassium levels in the 1:1 formulation (P1:OPC1) reached 7.18 grams per 100 grams of dry weight, three times higher than the control group (2.31 g/100 g). Phosphorus, zinc, and copper levels also saw substantial increases.

For instance, zinc content rose to 44.70 mg/kg in OPC-grown mushrooms (vs. 37.5 mg/kg in the control), while copper levels increased to 15.65 mg/kg (vs. 11.60 mg/kg). These minerals are essential for human health, playing roles in immune function, energy production, and enzyme activity.

Chemical Breakdown of OPC Supports Fungal Growth

FTIR spectroscopy, a technique used to analyze chemical bonds, revealed that OPC-based casing materials underwent significant structural changes during cultivation.

Fungal enzymes broke down complex compounds like cellulose, hemicellulose, and lignin—key components of plant cell walls—into simpler sugars that fueled mushroom growth.

Peaks in the FTIR spectra associated with cellulose (1020–1050 cm⁻¹) and lignin (1230–1270 cm⁻¹) decreased sharply in OPC treatments, indicating active degradation. In contrast, peat-only casing showed minimal changes, confirming that OPC’s organic structure is more conducive to fungal activity.

Environmental and Economic Benefits of OPC

The use of OPC in mushroom cultivation offers multiple advantages By repurposing OPC, the study addresses the disposal of 20 million tons of dry olive waste generated annually. This waste is often burned or dumped, contributing to air and water pollution.

Challenges and Future Directions

While the study demonstrates OPC’s potential, several challenges need addressing. For instance, the 1:1 peat-to-OPC ratio underperformed due to high phenolic content, which can suppress fungal growth. Pretreatment methods, such as composting OPC to reduce phenolics, could improve its suitability.

Additionally, OPC formulations had higher electrical conductivity (2.77–2.92 dS/m) than the recommended threshold (1.6 dS/m), potentially stressing mushrooms. Blending OPC with low-conductivity materials like coconut coir might resolve this issue.

Long-term studies are also necessary to evaluate OPC’s performance over multiple mushroom growth cycles. The current experiment lasted two harvest periods, but commercial farms require materials that remain effective over time.

Conclusion

This study establishes olive press cake as a viable, eco-friendly alternative to peat in Agaricus bisporus cultivation. Key takeaways include The 3:1 peat-to-OPC ratio boosts yields by 40% compared to peat alone. OPC-grown mushrooms are richer in protein, minerals, and antioxidants.
Using OPC reduces agricultural waste and supports sustainable farming practices. Involve optimizing OPC ratios for other mushroom varieties, scaling trials to commercial farms, and exploring OPC’s use as a soil conditioner in other crops.

By adopting OPC, the mushroom industry can reduce its environmental footprint, lower costs, and produce healthier food—benefiting farmers, consumers, and the planet alike.

Reference: Cetin, M., Atila, F. & Eren, E. Valorization of olive press cake as a sustainable alternative to peat in white button mushroom (Agaricus bisporus) cultivation. Biomass Conv. Bioref. (2025). https://doi.org/10.1007/s13399-025-06615-4

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