Effectiveness of dimethyl dicarbonate and potassium metabisulfite against spoilage yeasts and bacteria isolated from Tchapalo, a traditional Ivorian sorghum beer

Résumé fourni par la source

‘Tchapalo’, the Ivorian traditional sorghum beer, has a short shelf life, which represents one of the major constraints to its large-scale production, commercialization, and wider distribution. This study investigated the effect of chemical preservatives dimethyl dicarbonate (DMDC) and potassium metabisulfite (PMB) on spoilage-causing yeasts and bacteria isolated in ‘tchapalo’. For this purpose, ‘tchapalo’ was collected from the producers and then filtered using a 0.2 µm filter. Subsequently, cultures of 14 strains, comprising seven species of yeasts, five species of lactic acid bacteria (LAB) and two species of acetic acid bacteria (AAB), were prepared at an optical density of 0.1 at 620 nm. These were used to inoculate the filtered ‘tchapalo’ at a concentration of 0.3% in the presence of 0, 30, 60, 125, 200, 250 and 500 mg/L of each preservative. Samples were taken every 24 hours for three days to determine the microbial loads. The concentration inducing complete cell death upon addition to ‘tchapalo’ was regarded as the minimum inhibitory concentration (MIC). With the PMB the MIC of the yeasts species Kluyveromyces marxianus and Trichosporon coremiiforme was 200 mg/L. The most sensitive strains belong toSaccharomyces cerevisiae, Meyerozyma guilliermondii, Candida tropicalis, Rhodotorula mucilaginosa and Trichosporon asahii with MIC of 125 mg/L. With regard to DMDC, the MIC was 30 mg/L for Meyerozyma guilliermondii and Candida tropicalis, 125 mg/L for Rhodotorula mucilaginosa and 200 mg/L for Trichosporon asahii and Trichosporon coremiiforme. The most resistant strains belong to Kluyveromyces marxianus and Saccharomyces cerevisiae with MIC of 250 mg/L. The addition of 125 mg/L PMB resulted in a reduction in LAB counts compared with the untreated ‘tchapalo’. At this concentration, PMB exerted a bacteriostatic effect on the AAB species. In contrast, the LAB species isolated from ‘tchapalo’ showed low sensitivity to the different DMDC concentrations tested. For the AAB species, a minimum concentration of 200 mg/L DMDC was required to prevent cell proliferation. These preservatives, particularly PMB, may be recommended to extend the shelf life of ‘tchapalo’.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.