Enhancement of bioactive compounds in Haematococcus pluvialis through fermentation by glutamate-dependent Bacillus subtilis

In this study, a poly-γ-glutamic acid (γ-PGA)-rich fermented material was produced by fermenting Haematococcus pluvialis with Bacillus subtilis HA. To investigate the effect of monosodium L-glutamate (MSG) on bioactive compound production, fermentation media were supplemented with 0%, 5%, or 10% MSG. Viable cell counts increased from 7.50 log CFU/mL to 9.38, 9.08, and 9.52 log CFU/mL after 24 h in the 0%, 5%, and 10% MSG groups, respectively, followed by a slight decline at 48 h. MSG supplementation significantly enhanced mucilage production, reaching 3.90% in the 10% MSG group after 48 h, corresponding to 79.8% of the yield obtained in the defined medium (4.89%). In contrast, the control without H. pluvialis yielded 2.53%, whereas no mucilage was detected in the non-MSG group. The recovered mucilage consisted mainly of γ-PGA (81.49%), with smaller proportions of protein (13.22%) and carbohydrates (5.29%). Glucose consumption increased under MSG supplementation, whereas the MSG-free group exhibited the highest peptide content (270 μg/mL) and strongest antioxidant activity. Fermentation also increased total polyphenol content (9.3–16.8-fold) and enhanced α-glucosidase inhibitory activity. These findings demonstrate that H. pluvialis fermentation by B. subtilis HA enables the production of multifunctional food ingredients with tunable bioactive profiles.