The cryptophyte Rhodomonas salina is widely used in aquaculture due to its high nutritional profile. This study aims to investigate the effect of salinity and pH on the growth, phycoerythrin concentrations, and concentrations of non-volatile umami taste active compounds of R. salina, using a design of experiment approach. Rhodomonas salina was cultivated in a flat-panel photobioreactor in turbidostat mode in a range of salinity (20–40 ‰) and pH (6.5–8.5). The strain was able to grow steadily under all conditions, but the optimal productivity of 1.17 g dry weight L−1 day−1 was observed in salinity 30 ‰ and pH 7.5. The phycoerythrin concentration was inversely related to productivity, presenting higher values in conditions that were not optimal for the growth of R. salina, 7% of dry weight at salinity 40 ‰, and pH 8.5. The identification of the umami taste of R. salina was based on the synergistic effect of umami compounds 5′-nucleotides (adenosine 5′-monophosphate, guanosine 5′-monophosphate, inosine 5′-monophosphate) and free amino acids (glutamic and aspartic acids), using the equivalent umami concentration (EUC). The results indicated that an increase in pH induces the accumulation of 5′-nucleotides, resulting in an EUC of 234 mg MSG g−1 at a salinity of 40 and pH 8.5. The EUC values that were observed in R. salina were higher compared to other aquatic animals, a fact that makes R. salina promising for further research and application in the food and feed sectors.

Rhodomonas salina is a microalgal species, belonging to the cryptophytes, and is widely used as aquaculture feed because of its high nutritional profile and phycoerythrin content. This study investigated the effect of pH on the growth, biochemical composition, and taste of R. salina when cultivated on a semi-large scale under natural light conditions. Two tubular photobioreactors (200 L) were used for the cultivation of R. salina with sunlight as the only illumination source. Two different pH setpoints were applied, 7 and 8.5. Optimal temperature and nutrient conditions were applied, according to previous research findings. The results demonstrated that the productivity of R. salina was higher at pH 7, 0.06–0.14 gdry weight L−1 day−1, compared to pH 8.5, 0.03–0.12 gdry weight L−1 day−1. It was found that protein and total fatty acid concentrations were higher in the biomass that was produced at pH 8.5, 33.7% and 12.3% of dry weight, respectively, while at pH 7, the protein content was 31.9% and the total fatty acids 8.8% of dry weight. The phycoerythrin concentration, like protein, was higher at pH 8.5, 2.7% of dry weight, compared to pH 7, 1% of dry weight. The free amino acid and nucleotide profile of R. salina was affected by the pH, resulting in increased equivalent umami concentration at pH 7. For the sensory evaluation, an expert panel on algae flavors evaluated the effect of pH on the taste of R. salina, reporting that the biomass that was produced at pH 7 had more umami flavor than the biomass that was produced at pH 8.5, which was evaluated as more bitter.