Utilizing straw-derived hemicellulosic hydrolysates by Chlorella vulgaris: Contributing to a biorefinery approach

Abstract

With the growing human population, greenhouse gases and global temperature are increasing calling for sustainable biorefineries to convert low-value side streams into high-value products. In this study, the remaining hemicellulosic sugary waste fraction of a wheat straw biorefinery approach, without any pretreatment, was applied as a medium supplement for Chlorella vulgaris cultivation. Next to oligomeric and monomeric sugars, the waste stream contained hydrolysis by-products, such as furfural, 5-hydroxymethylfurfural and acetic acid. Despite the presence of these growth inhibitors, C. vulgaris cultivation was possible. Addition of 2.5% (v/v) of wheat straw hydrolysate to BG11-medium boosted chlorophyll content in C. vulgaris by 40% compared to photoautotrophically grown cells solely cultivated on defined media. As of now, this is the highest chlorophyll content obtained from a cultivation of C. vulgaris on a medium supplemented with a waste stream. Overall, our results demonstrate that wheat straw hydrolysate increases chlorophyll biosynthesis, improving the nutritional value of C. vulgaris biomass for food and feed applications. Hence, valorization of this hemicellulosic sugary fraction results in an additional high-valued product contributing towards the wheat straw biorefinery.