The effect of aqueous extract of coconut milk on the growth of Lactobacillus fermentum under oxidative stress

Oxidative stress negatively affects the growth and survival of lactic acid bacteria (LAB) under aerobic conditions. This effect may limit the technological and probiotic applications of LAB. Plant phenolic compounds possess antioxidant activity and may enhance bacterial tolerance to oxidative stress. The present study investigated the protective antioxidant effects of the aqueous extract of coconut milk (AECM) on Lactobacillus fermentum under aerobic conditions. AECM was chemically analyzed to determine its total phenolic content, ortho-diphenol content, and protein content. Antioxidant protection was assessed using two experimental approaches: aerobic growth in the presence of AECM and aerobic growth after overnight pre-treatment with AECM. AECM contained 97.11 μg mL⁻¹ total phenolics, of which approximately 16% were ortho-diphenols. The protein content was 1.11 mg mL⁻¹ in the AECM. During aerobic growth on solid medium, the presence of AECM resulted in a significant 16.5% increase (p < 0.05) in colony-forming units (CFU) compared to the controls. Pre-treatment with AECM resulted in a stronger protective effect, with an approximately 49 % increase in CFU during subsequent aerobic growth (p < 0.05). No significant differences were observed under anaerobic conditions, indicating that, at the concentrations used, AECM mitigates oxidative stress rather than exerting nutritional support. These findings demonstrated that AECM confers antioxidant protection to L. fermentum through both direct and inducible antioxidant mechanisms, and reinforced previous observations on the inducible antioxidant protection of coconut milk phenolics conferred in several LAB species, including L. fermentum.