Title : Enhancement of bioactive polymers in Chlorella pyrenoidosa using moderate electric field-based fermentation
Abstract:
Microalgae represent a highly promising resource for new food materials due to their environmentally sustainable nature, high nutritional value (e.g., essential amino acids, bioactive peptides, omega-3 fatty acids, and polyphenols) and resilience to climate variability, allowing for stable cultivation and harvesting. To utilize that, innovative microbial fermentation technology was employed to convert it into high value-added materials. Aiming to evaluate the effect of square-waving Moderate Electric Field (MEF) on bioconversion using glutamate as a substrate for glutamate synthetase in Bacillus subtilis, this study compares the efficiency of conventional fermentation (CF) with that of electro-fermentation (EF) to produce poly-γ-glutamic acid (γ- PGA). The medium used for the growth of the strain was composed of 1% Chlorella, 2% glucose, and 10% monosodium L-glutamate (MSG). The B. subtilis starter culture was pre-incubated in 5% skim milk for 24 hours before being inoculated at a concentration of 5%. In the same conditions, MEF-assisted fermentation was conducted using an alternating current (AC) of 0.6 A, 50% duty cycle with a square-pulse waveform for 48 hours. After 12 hours, the viable bacterial count demonstrated a logarithmic growth rate of 31.08% compared to the initial state. Additionally, the production capacity of mucilage showed an approximately 21.94% increase compared to conventional fermentation methods. Chlorella, a protein-rich material, was hydrolyzed into lower molecular weight compounds by the protease activity of B. subtilis, leading to a progressive increase in tyrosine content over the culture period. The tyrosine concentrations of final products were 5,491 ppm for CF and 5,685 ppm for EF. Overall, EF indicated superior production yields of bioactive compounds relative to CF, primarily attributed to augmented enzymatic activity. This improvement is hypothesized to arise from increased cell membrane permeability in microorganisms, which is induced by electropermeability under electrical stimulation. Consequently, Chlorella-based material metabolized by B. subtilis is enriched with γ-PGA, peptides, and probiotics, making it a sustainable food additive for the food industry. Also, EF offers a promising pathway for the establishment of a novel paradigm in bioconversion processes, potentially transforming future biotechnological applications through substantial improvements in efficiency and technological innovation.
