Optimization of benzo[α]pyrene degradation by <i>Enterococcus faecium</i> using response surface methodology

Benzo[α]pyrene (BaP) is a persistent organic pollutant that is notoriously difficult to remove. Here, we report the isolation of a novel BaP-degrading probiotic, <i>Enterococcus faecium</i> MA-4, from Kefir grains. Four factors for degradation of BaP by MA-4 were obtained through single factor test: pH 7, temperature 37°C, BaP concentration 10 mg L^-1, inoculum size 15%. Employing a Box-Behnken design within response surface methodology, the study investigated the impact of pH, temperature, BaP concentration, and inoculum size on the degradation rate of BaP by MA-4, aiming to enhance its degradation kinetics. The results revealed that the inoculum size was the predominant factor affecting degradation. Under optimal conditions, pH 6.5, an initial BaP concentration of 7 mg L^-1, a temperature of 35°C, and an inoculum size of 10%, the degradation rate of BaP by MA-4 was enhanced to 61.52%. Analysis of Variance confirmed the model's accuracy with a significant <i>F</i>-value of 12.03 at <i>p</i> < 0.0001 while the quadratic regression model showed a high <i>R</i>² value 0.9232. <i>R</i>²adj (0.8465) closely matches <i>R</i>²pred (0.6506). Adeq Precision(10.986) and Lack of Fit (<i>F</i>-value = 0.99) both demonstrate the reliability of the model. The probiotic MA-4 effectively degrades BaP, showing promise for food-grade applications in BaP mitigation. However, the application of <i>Enterococcus faecium</i> requires rigorous safety assessment due to their potential as opportunistic pathogens. This study provides key theoretical and practical guidance for the probiotic-based remediation of BaP in foodstuffs.