Spectral and Growth Response of Lactococcus lactis to Monascus Pigment under Red LED Illumination

다국어 초록 (Multilingual Abstract)

This study investigated the combined effects of Monascus pigment concentration and red LED (RLED) illumination on the growth of Lactococcus lactis, pigment stability, and pH variation during fermentation. The Monascus pigment (0.1-10 mg/mL) and RLED (λ ≈ 660 nm) were applied to evaluate microbial and optical responses. The pigment showed no antibacterial activity against Staphylococcus aureus below 100 mg/mL, indicating safety for use in lactic fermentation. Spectrophotometric analysis revealed that high pigment concentrations caused optical saturation, whereas 2.5-5 mg/mL maintained balanced color intensity and bacterial growth. Under LED irradiation, the colorant exhibited stable absorbance with no visible photodegradation, confirming high photostability under low-energy red light throughout the fermentation period. L. lactis showed slightly accelerated growth and faster acidification within 24 h; however, viable cell counts converged after 48 h, indicating that the observed effects were limited to the early fermentation stage and likely reflect transient photobiomodulation of microbial metabolism. Overall, these findings indicate that low pigment concentrations combined with RLED can support pigment stability and microbial activity without inducing adverse effects on cell viability or fermentation performance. This study highlights the potential applicability of RLED-assisted fermentation systems incorporating natural colorants as a controllable and stable approach for fermentation process optimization.