Evaluation of Yoghurts with Thyme, Thyme Essential Oil and Salt

Abstract

The aim of this work was production and evaluation of yoghurts with different addition of thyme (Thymus vulgaris), thyme essential oil (EO) and salt. It was produced: control yoghurt, yoghurt with 0.45 % of salt and 0.25 % of thyme, yoghurt with 0.90 % of salt and 0.50 % of thyme, yoghurt with 0.45 % of salt and 0.004 % of thyme EO, yoghurt with 0.90 % of salt and 0.008 % of thyme EO. The time of yoghurt fermentation was extended from the previous 3.5 hours (control sample) to 5 hours for samples with thyme or even up to 7 hours for samples with thyme EO. The fermentation time also depended on the concentration of the used substances. The average titratable acidity of yoghurts fluctuated from 46.52 °SH to 49.51 °SH at day after the production and from 51.57 °SH to 55.75 °SH after 7 days of storage. Average pH values of yoghurts fluctuated from pH 4.77 to pH 4.81 at day after production and from pH 4.48 to pH 4.63 after storage. In all samples of yoghurts were not detected coliform bacteria (< 10 CFU.g-1). The yeasts were appeared rarely (101 CFU.g-1), and their numbers were increased during cold storage (102 up to 103 CFU.g-1). Moulds appeared rarely (101 CFU.g-1). The number of lactic acid bacteria reached required minimum value of 107 CFU.g-1. Samples of yoghurts reached characteristic yoghurt and thyme aroma. The intensity of sour, salty and thyme taste, determined by sensory evaluation was in experimental samples of yoghurts at different level. A higher concentration of thyme and thyme EO gave to yoghurts a bitter taste. The dense consistency of the yoghurts was decreased with the increased addition of thyme and thyme EO. According to results, we recommend the recipe of yogurt with 0.45 % of salt and 0.25 % of thyme or 0.004 % of thyme EO.