Protein production in Spirulina platensis biomass using beet vinasse-supplemented culture media

• Cultivation of Spirulina platensis in a tubular airlift photobioreactor.
• Use of mineral medium supplemented with beet vinasse.
• Determination of biomass and protein productivities.
• Beet vinasse (1 g L−1) stimulated protein productivity in Spirulina platensis.
• Higher vinasse concentration (2 g L−1) did not further improve productivities.

Beet vinasse is a by-product from molasses fermentation factories, which is difficult to dispose of and involves a severe environmental concern. The present work deals with the valorisation of beet vinasse by means of the protein production in Spirulina platensis biomass. A preliminary study was firstly planned in batch flasks to analyse the influence of environmental factors on S. platensis protein content and protein productivity in beet vinasse supplemented culture media. Experimental conditions were selected to operate the photobioreactor that could provide a balance between protein content and cell growth. Then, S. platensis was cultured in an airlift tubular photobioreactor using mineral medium supplemented with beet vinasse (SVM media). The maximum cell concentration and protein productivity achieved in the tubular photobioreactor were 6.5 ± 0.7 g L−1 and 168 ± 18 mg L−1 d−1, respectively (with SVM 1 g L−1 of vinasse). The addition of a higher vinasse concentration (SVM 2 g L−1) led to biomass concentration and protein productivity values (3.6 ± 0.3 g L−1 and 86 ± 6 mg L−1 d−1, respectively) closer to those achieved using unsupplemented mineral medium. Stable biomass concentrations were maintained during the continuous operation, thus demonstrating the ability of S. platensis to adapt to these culture media.