Essai de conservation d’un yaourt brassé par l’extrait de myrte

Abstract

The objective of this work is to study the effects of the incorporation of Myrtus communis L. essential oil on the quality of stirred yogurt prepared and fermented by freeze-dried lactic ferments in the laboratory. The essential oil was incorporated at concentrations of 2.5%, 5% and 10% in the yogurt during the stirring process. These effects were evaluated by monitoring the evolution of the physico-chemical and microbiological parameters during 21 days of storage at + 4 ° C. The presence of the essential oil at the concentrations of 2.5%, 5% and 10% in the stirred yogurt led to an increase of St. thermophilus viability in the order of 33.7x106, 31x106 and 53.2x106 UFC/ml from the first week of storage and then a significant decrease with the highest doses of 5% and 10% in the order of 11 × 106 and 19 × 106 CFU/ml, respectively, at the end of storage. On the other hand, the addition of the essential oil at a low dose of 2.5% showed a slight decrease of 1.3x107 CFU/ml at the end of storage comparable to that of the control (1.2x107 CFU/ml). As for the acidity, the results obtained showed a decrease in pH (from 4.6 to 3.9 for 10%, from 4.6 to 4.2 for 5% and from 4.6 to 4.35 for 2,5% of EO) and an acidity increase of 85 to 135 ° D for 10% and 84 to 112 ° D for 5% with exception for 2.5% (81 to 94 ° D) compared to the control (83 to 125 ° D). Thus the addition of this dose made it possible to stabilize the microbiological quality of the stirred yogurt while extending its shelf life. Sensorially, natural yogurts (sugar-free and with sugar) were the favorites among all samples and aromatization with myrtle EO at a dose of 5% seems to be the least appreciated or even unacceptable because of its strong aroma, pronounced odor and accentuated taste.