Antifungal activity of lactic acid bacteria isolated from kunu-zaki, a cereal-based Nigerian fermented beverage
Omotade R. Ogunremi, Susette Freimüller Leischtfeld, Sandra Mischler, Susanne Miescher Schwenninger
Abstract
Fungal deterioration is a barrier to the wide acceptance of fermented cereal foods from Africa. The use of protective cultures is a natural approach to controlling fungi in foods that also complies with a clean label strategy. This study aims to select antifungal lactic acid bacteria (LAB) previously isolated from kunu-zaki to bio-control deterioration in this cereal-based Nigerian fermented beverage. Strains of Leuconostoc citreum (1), Limosilactobacillus fermentum (6), and Weissella confusa (3) were the most active against seven test mold species, with average inhibition score of 2.25–2.88, after screening 220 LAB strains using agar overlay on millet-sorghum flour hydrolysate (MSFH) agar. The MSFH agar diffusion method revealed that antifungal activity against the seven target molds was retained in cell-free supernatants (CFSs) of selected LABs, with the strongest inhibition against A. flavus F008BA and P. citrinum 3AS1 demonstrated by L. fermentum 5KJEU5 (9.06%) and W. confusa YKDIA1 (24.55%), respectively. The antifungal activity of CFSs was mainly due to the occurrence of acidic compounds, with the most abundant compounds being acetic (0.30–1.96 mg/mL) and lactic (1.80–3.23 mg/mL) acids. Other compounds such as hydroxycaffeic (0.16–6.72 μg/mL), 3-(4-hydroxyphenyl) propionic (1.40–6.36 μg/mL), 3-phenyllactic (1.28–24.48 μg/mL), and hydroxyferulic acids (12.25 μg/mL) occurred at lower concentrations. In challenged kunu-zaki, L. fermentum 5KJEU5 prevented the growth of A. flavus F008BA and P. citrinum 3AS1 beyond 8 day at ambient temperature (25 °C). In this study, LAB from kunu-zaki displayed strong antifungal activity, showing great potential as a protective culture to prevent fungal growth and mycotoxin accumulation in cereal foods.