Etude bactériologique de lait de vache pasteurisé réfrigéré additionné d’un extrait naturel

Abstract

Pasteurized milk, despite the applied heat treatment, remains susceptible to microbial alteration during storage. The use of natural compounds of plant origin is attracting increasing interest to improve its microbiological stability. The present work aims to evaluate the effect of the addition of the aqueous extract of Cymbopogon citratus on the dynamics of overall microbial growth and the physicochemical quality of pasteurized milk during its refrigerated storage. Three concentrations of the aqueous extract were tested to determine the kinetic parameters of bacterial growth (initial X, max X, max μ and the lag phase λ) : 10 mg/mL (C1), 5 mg/mL (C2) and 2.5 mg/mL (C3), comparing with a control without addition. The evolution of pH and titratable acidity (°D) were also monitored. The aqueous extraction yield of lemongrass was satisfactory, 10.697%, and the results obtained showed that its addition to milk did not significantly inhibit microbial growth compared to the control sample. The values of X initial (3.65 to 3.89 Log CFU/mL) and X max (8.521 to 8.703 Log CFU/mL) remained close to those of the control (3.77 and 8.431 log CFU/mL respectively). Similarly, the specific growth rates (μ max) did not show a marked decrease, even reaching slightly higher values for some concentrations (up to 1.02 Log CFU/mL/h for C1). The lag phase also varied slightly (1.432 to 1.624 h), without significant delay in microbial growth. Regarding acidity and pH, a gradual increase in acidity and a decrease in pH were observed in all samples over time, reflecting the metabolic activity of lactic acid bacteria during storage. We can conclude that the C. citratus extract, at the tested concentrations and in aqueous form, did not exert a significant preservative effect on the total mesophilic aerobic flora of pasteurized milk.