Potential antifungal activity of essential oil from Cymbopogon citratus (DC) Stapf and its performances as biostabilization of tiger nut milk (Cyperus exculentus)

Tiger nut milk is not heated during processing and is usually contaminated with spoilage microorganisms due to its high starch content. The present study aims to preserve tiger nut milk using essential oil from Cymbopogon citratus as an antimicrobial agent. The antifungal activity was evaluated by agar diffusion and micro-dilution methods. Storage tests were performed at 4°C by incorporating tiger nut milk with different concentrations of EO (i.e. 0.05; 0.10; 0.15; 0.20; 0.25; 0.30; 0.35; 0.40; 0.45 and 0.50 (% v/v)), after which the physicochemical and hygienic characteristics were assessed. The EO showed significant (p ˂ 0.05) inhibitory activity against A. niger (19.89 mm), C. albicans (26.30 mm), C. kefir (26.45 mm), C. tropicalis (27.31 mm), R. nigricans (27.45 mm) and S. cerevisiae KVL013 (25.52 mm) with MICs 15.62 (A. niger), 0.98 (C. albicans), 1.63 (C. kefir), 1.95 (C. tropicalis), 7.81 (R. nigricans) and 0.98 (S. cerevisiae KVL013). The results of the shelf-life monitoring showed that the milk samples were free of total and thermotolerant coliforms, Bacillus spores and sulphite-reducing anaerobes spores. At a concentration of 0.40 to 0.50% of EO and after 21 days, flora microbial load decreased in unpasteurized milk from 103 to 102 (CFU/mL) and yeasts/moulds decreased from 102 to 101 (CFU/mL), whereas in pasteurized milk, flora decreased from 103 to 10 (CFU/mL), and yeasts/moulds decreased from 102 to less than 101 (CFU/mL). This shows that the tiger nut milk remained stable and its hygienic quality complied with the standards set for spoilage flora and spores for 21 days at 4°C under refrigeration. The results obtained indicated that EO of C. citratus has strong antimicrobial activity on spoilage flora and the stabilisation concentration can be modulated for sensory acceptability.