Photobiomodulatory Interactions between Debaryomyces hansenii and Monascus Pigments under Red LED Irradiation

This study investigated how different inoculation concentrations of Debaryomyces hansenii interact with red pigments derived from Monascus sp., with a focus on pigment absorbance, yeast growth, and pH behavior under red LED (RLED) illumination. To clarify these responses, inoculation level, pigment concentration, and light exposure were systematically compared. Monascus pigments show photoreactivity that may influence cellular redox balance, thereby affecting yeast metabolism. The 1% inoculation group exhibited a faster and higher increase in absorbance at 600 nm than the 0.1% group. Under RLED, pigment mixtures reached saturation at 490 nm within 10–50 mg/mL, indicating interaction effects at ≤10 mg/mL. Yeast growth did not differ between illuminated and dark groups without pigments, while pigment-containing cultures shifted from neutral pH to 3–4. Pigment addition inhibited yeast proliferation, with the strongest inhibition under pigment + RLED conditions. In contrast, RLED alone modestly enhanced yeast viability (~10%) at 48 h, suggesting a slight growth-promoting effect. Overall, the combined influence of pigments, inoculation level, and RLED revealed distinct patterns of pigment stabilization and yeast suppression, demonstrating that red-light modulation may support pigment integrity while controlling yeast activity, offering potential applications in fermented food production and light-assisted culture processes.