Single-cell protein production by Pleurotus ostreatus in submerged fermentation

Abstract

Agricultural land shrinkage, decreasing global water resources, population increase and malnutrition highlight the need for new food sources. Single-cell protein derived from microorganisms could be a solution to high protein demand. The aim of this work was to optimize the cultivation conditions for single-cell protein production by Pleurotus ostreatus LGAM 1123 in submerged cultures and valorize fiber sludge, a low cost industrial side stream from the pulp and paper industry, as a substrate for single-cell protein (SCP) production. A study on the effect of different cultivation conditions on fungal growth and protein production has been conducted. Response surface methodology was used to investigate the combined effect of the most important factors (glucose and yeast extract medium concentrations) and optimize the process. A maximum protein production of 10.0 ± 0.9 g L⁻¹ was found for the submerged cultivation of the fungus in a 3.5 L stirred-tank bioreactor, while the biomass produced and its total protein content were 26.0 ± 2.0 g L⁻¹ and 44.8 ± 0.8%, respectively. As an industrial application, a cellulosic hydrolysate obtained after enzymatic hydrolysis of fibre sludge in the optimized medium composition was used. Fibre sludge was shown to be an excellent feedstock for SCP production achieving productivity and protein content very similar to glucose fermentations. Single-cell protein of P. ostreatus presented higher amino acid scores compared to the recommended ones for valine, leucine, and aromatic amino acids in human nutrition. Therefore, P. ostreatus biomass could stand as an alternative vegan protein source due to its high protein content and amino acid composition.