Tisochrysis lutea biomass as a substrate for lactic acid fermentation

Microalgae contain high quality proteins, polyunsaturated fatty acids and bioactive molecules endowed with beneficial properties (Lafarga et al., 2021). They are, thus, considered interesting candidates for nutraceuticals and functional foods (Matos et al., 2017). The uses of microalgae in food production include the development of functional fermented foods. Lactic fermentation allows to add the beneficial effects of probiotic bacteria to the useful biomolecules lying in microalgal biomass, also taking advantage of the effects on organoleptic features produced by fermentation. The aims of this work were to evaluate the potential of Tysochrysis lutea F&M-M36 lyophilized biomass as a substrate for Lactiplantibacillus plantarum ATCC 8014 fermentation, as well as to investigate the effects of the indigestible fraction of the microalgal biomass on bacterial growth, and to verify whether the microalgal biomass could exert a protective role towards the probiotic bacterium during a simulated digestion process. Initially, three lactobacilli were characterized for growth and resistance to simulated digestion, then the best strain (L. plantarum ATCC 8014) was selected for the fermentation trial. This latter was set up with T. lutea F&M-M36 raw and digested biomasses suspended in two different matrixes. The biomasses obtained at the end of the fermentation trial were analyzed for gross biochemical composition, digestibility and radical scavenging activity and compared with the unfermented biomasses; moreover, survivability of L. plantarum ATCC 8014 to in vitro digestion was also evaluated. The higher growth and organic acid production was observed with microalgal raw biomass suspended in diluted organic medium. No protective effect on bacterial survivability was observed after fermentation. Radical scavenging activity of a lipophilic extract was higher in fermented than in raw microalgal biomass and was also higher than in the fermented post-digestion residue. Fermentation seems an interesting process to obtain functional foods from T. lutea, although further investigation is needed to optimize the matrix for fermentation so as to improve bacterial growth, and thus fully elucidate the role of fermentation for functionality improvement.