Industrial by-product like orange peel plays an important role in pectin manufacture. The objective of this article was to extract pectin from peel of Citrus sinensis and to study the effect of its incorporation on the quality of yogurt during the period of fermentation and postacidification. Physicochemical, organoleptic, and rheological properties of yogurt prepared with pectin were studied in order to determine the best preparation depending on the rate of pectin. The extraction pectin yield was estimated to more than 24%. The viscosity and acidity were increased with increasing of the pectin rate. The best viscosity value was obtained with 0.6% of pectin. Furthermore, the effect of the rate of pectin incorporation in the fermented milks was clearly observed on the number of Streptococcus thermophilus and Lactobacillus bulgaricus, the cohesiveness, the adhesiveness, the taste, and the whey exudation. 359

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The aim of this work was to evaluate the effect of Thymus vulgaris L phenolic extracts (TVPE) on the growth of Streptococcus thermophilus and Lactobacil- lus delbrueckii subsp. bulgaricus, and the impact of their addition in small amounts (2-8%) to a set-style yogurt with regard to variations in physico- chemical, bacteria count and organoleptic properties during 21 days storage at 4°C. The phenolic components were extracted from the crushed aerial parts of the test plant by cold maceration in hydromethanolic solution (methanol: water, 80:20 v/v). The plant polyphenolic profile was determined by HPLC. The survival ability of yogurt starter cultures in the presence of TVPE was evaluated through the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The total phenolic content (TPC) was 20.2 ± 0.57 μg GAE / mg extract. The amount of  flavonoid compounds was 39.83 μg EQ/mg extract. As the quantitative measurements revealed, apigenin and fisetin (8.17, 6.83, μg GAE /mg extract respectively) emerged as major phenolic compounds from thyme aerial parts. The MIC and MBC against the growth of both lactic bacteria were obtained at 60% of TVPE concentration. A significant (p< 0.01) changes in pH, trable acidity and apparent viscosity were observed in all experimental yogurts. The best scores of sensory evaluation were recorded in samples added with 2% and 4% of TVPE as well as the control. Based on collected data, 2% and 4% of TVPE can be incorporated into yogurt without risk of deterioration in physicochemical quality or inhibition of lactic bacteria.

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