Formate and propionate were also present in minor concentrations, whereas isobutyrate and isovalerate were only detected in
the fermentations by LE37. The later organic acids have been identified as resulting from the proteolytic fermentation of aminoacids
by anaerobic bacteria, particularly from L-leucine and L-valine, with
the production of CO2 [45–47]. Their production might have contributed to the higher amount of CO2 detected in the fermentations
by LE37 or including LE37 (Table 1). Conversely, C. butyricum
achieved a high H2 production with all the microalgal loads tested
with a simultaneous high H2/CO2 ratio. In spite of the need of carrying out the fermentation under aseptic conditions, pure cultures
are more predictable than mixed cultures in terms of co-produced
metabolites passible of further upgrading.