Heterotrophic single-cell protein production in Galdieria sulphuraria: protein content and bioaccessibility

Abstract

Aim: This work aimed to explore the potential of the polyestremophilic microalgae Galdieria sulfuraria for single-cell protein production. To this end, four G. sulphuraria's strains were cultivated heterotrophically and compared for their protein content and bioaccessibility. Method: Four G. sulfuraria strains were selected: two strains known to maintain their blue-green colour during heterotrophic cultivation while the other two were known to lose pigmentation in heterotrophy. The four strains were cultivated in an inorganic medium at pH 1.8±0.3, containing 20 g/L glucose. The experiments were conducted in flasks using six biological replicates. Two flasks were harvested during the exponential phase , two immediately after glucose depletion, and the last two 24 (S24) and 48 (S48) hours after substrate depletion. We compared protein content and bioaccessibility (INFOGEST 2.0) during the different growth phases. Results: The strains had an exponential growth rate between 0.90 and 1.65 day-1. After substrate depletion, the growth was terminated and dry weight decreased 12-17% from E and S48 . Substrate depletion strongly affected protein content and bioaccessibility. In three strains protein content increased from 33% w/w during the exponential phase to 53% w/w in S24, while their bioaccessibility was halved, from 65% in exponential phase to 32% in S24. One strain instead showed signifincantly higher protein content, 50% w/w in exponential phase and 75% w/w in S24, while its bioaccessibility remain constant (65±3%) throughout the whole experiment. Conclusion: Our results highlight the large variation in protein content and bioavailability among G. sulphuraria strains during different growth phases. Selecting the right strain and harvesting at the right time are keys for efficient single-cell protein production.