Mycobiota and co-occurrence of mycotoxins in South African maize-based opaque beer

Abstract

Beer, a beverage consumed throughout the world, is mainly derived from cereals. In this study, fungal and mycotoxin contamination, as well as the physicochemical properties of maize-based opaque beer (umqombothi) obtained from the Gauteng province of South Africa, was investigated. The mean water activity, pH and total titratable acidity of the analysed beer samples were 0.91, 3.76 and 1.20% lactic acid, respectively. The investigation revealed Aspergillus, Penicillium, Phoma and Saccharomyces as the predominant fungal genera with a mean fungal load of 3.66 × 10⁵ CFU/mL. Among the mycotoxigenic fungal species recovered, Aspergillus flavus had the highest incidence of 26%. Previously unreported strains such as P. chrysogenum strain AD25, A. sydowii strain AD 22 and A. tritici strain AD 11 were found. Furthermore, mycotoxin quantitative analysis via liquid chromatography-tandem mass spectrophotometry showed that deoxynivalenol was the dominant mycotoxin occurring in 84% of the samples. This was followed by enniatin B that occurred in 75% of samples ranging from 12 to 44 μg/L and fumonisin B₁ (FB₁) (incidence of 53% at a maximum level of 182 μg/L). Generally, there was low occurrence aflatoxins, whereas T-2, HT-2, nivalenol, zearalenone, 3- and 15-acetyl-deoxynivalenol were not detected. All the samples analysed had safe levels of mycotoxins tested but were contaminated by at least two mycotoxins that could pose some additive or synergistic health effects among consumers. On average: a 60 kg adult consuming 1-6 L/day of the beer was exposed to FB₁ + FB₂ at an estimated 2.20-13.20 μg/kg body weight/day. These values were far above the maximum tolerable daily intake of 2 μg/kg bw/day established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA). The study demonstrates that consumption of umqombothi can significantly enhance dietary exposure to multiple mycotoxins among consumers, and therefore accentuates the need for strategies aimed at reducing toxigenic fungal colonization and mycotoxin contamination in the beer processing chain.

Keywords: Beer; Fungi; Maize; Mycotoxins; South Africa.