Elsevier

Biomass and Bioenergy

Volume 35, Issue 7, July 2011, Pages 3276-3279
Biomass and Bioenergy

Short communication
Recovering low molecular weight extractives from degraded straw by oyster mushroom at the farm scale for high value use

https://doi.org/10.1016/j.biombioe.2011.04.051Get rights and content

Abstract

During the cultivation of mushrooms on straw, the degradation of lignocellulose takes place under the action of enzymes releasing degradation products with small molecular weight, some of which are potentially valuable (sugars, phenolics, fatty acids, etc). These compounds may be extracted from straw after mushroom cultivation in two stages: an aqueous extraction followed by a solvent extraction. The present work is focused on the first stage of the process where water soluble compounds are extracted. It is important to conduct experiments at a scale that would reflect the amount of waste straw generated by a mushroom farm. A study was performed using a vessel of 300 L capacity with mixing impeller, by observing the influence of the temperature, extraction time and water-to-dry straw ratio on the total extracted matter and especially on sugar and phenolic compounds yields. The optimum extraction conditions were determined by taking into account the yields. From this study, it emerged that the room temperature is recommended, the water-to-straw ratio would not exceed 40:1 kg kg−1 of dry straw and the extraction time should be limited to 4 h.

Highlights

► Degraded straw after the cultivation of the oyster mushroom exploited to recover valuable products. ► Aqueous extraction performed at the farm on a scale relevant to the mushroom cultivation industry. ► The water-to-straw ratio should be kept as low as possible. ► The extraction time should be limited to 4 h. ► The optimum temperature for the extraction is the room temperature.

Introduction

The mushroom cultivation industry employs naturally occurring lignocellulose-degrading fungi in a solid state fermentation at ambient temperatures [1], [2] to convert straw into high value products, e.g. the oyster mushroom Pleurotus ostreatus [3] or the button mushroom Agaricus bisporus [4]. An integrated biorefinery model may be applied not only to produce mushrooms, but also to extract useful compounds from the residual degraded straw, e.g. C5 and C6 sugars and phenolics for biofuel production, pharmaceutical use, etc. We aim to develop a two stage extraction process to separate these compounds: an aqueous extraction followed by a solvent extraction, under mild conditions. This process can potentially be performed locally, at farm scale. In a previous work [5], the optimum conditions of the extraction process were determined at the laboratory scale. However, it is essential to develop the optimum process at real scale, i.e. a mushroom farm dealing with the disposal of tones of straw.

The present work is focused on the first stage of the process, the aqueous extraction. A study was performed using a vessel of 300 L capacity with mixing impeller, where the influence of the temperature, processing time and water-to-dry straw ratio were assessed for the extraction of total extracted matter and especially sugar and phenolic compound yields. Optimum extraction conditions in terms of product release were identified.

Section snippets

Raw material

The raw material for the study consisted of wheat straw degraded by fungus Pleurotus ostreatus grown in approx 20 kg batch in plastic bags under standard cultivation conditions at the WHRI, University of Warwick, Bioconversion Unit. Briefly, straw was pasteurized for two days in the pasteurization tunnel at 70 °C and atmospheric pressure (using steam from a boiler at 0.3 MPa and 140 °C), then inoculated with P. ostreatus (strain HK35) at a rate of 1.5 kg grain spawn to 100 kg straw, the fungus

Results and discussion

The total matter extracted, the organic carbon and the quantities of sugars and phenols recovered were measured and compared in different extraction conditions.

Conclusions

This study aimed to consider whether the partially degraded straw remaining following the cultivation of the oyster mushroom, P. ostreatus, could be exploited to release lignocellulose breakdown products on a scale relevant to the mushroom cultivation industry.

The aqueous extracts obtained in this process may have potential application in the production of biogas, due to the high content of organic carbon.

In this study a vessel of 300 L capacity was used, reflecting the scale of the process

References (8)

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Cited by (1)

  • A membrane screening for the separation/concentration of dilignols and trilignols from solvent extracts

    2012, Separation and Purification Technology
    Citation Excerpt :

    The extracts were obtained by contacting at room temperature for 24 h the solvent with the straw degraded by Pleurotus ostreatus (the oyster mushroom). The authors of the present work described the growth of the mushroom on wheat straw in [27]. The solvent extraction can be preceded by an aqueous extraction.

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