Production and quality assessment of a set-style yogurt fortified with low concentrations of Thymus vulgaris L phenolic extracts

Abstract

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.

Antioxidant potential, lipid profile and sensory attributes of a functional yogurt formulated with hydroethanolic extract of Mentha Piperita L.

“…This could be explained by the decline in the production of exopolysaccharides by the St and Lb lactic ferments, whose proliferation and ability to elaborate these complex carbohydrates in the medium seem to be altered by the phenolic compounds of HEEMP, given that the rheological quality of yogurt, represented mainly by the sticky and cohesive criteria, is proportionally linked to the amounts of exopolysaccharides produced by St and Lb bacteria (Rawsan & Marshal, 1997). Our results are in line with those of several authors who have observed a drop in the rheological quality of yogurts during storage at 4°C, following the antimicrobial effect against these two germs exerted by the phenolic compounds of hydroethanolic extracts of Thymus vulgaris L. (Kheli et al, 2018) and Mentha piperita L. (Ait Chabane et al, 2021), added notably at a high dose of 6%. Moreover, throughout the storage period, yogurts with 2% and 4% HEEMP were better evaluated and appreciated than the control, probably due to the manifestation of a pleasant mixture of odors combining the aromatic components brought by the mint extract, such as menthol, menthone, and limonene (Djenane et al, 2012), and those generated by the fermentative activity of the yogurt bacteria, such as diacetyl, acetaldehyde, and acetone (Beshkova et al, 1998).…”

Enhancement of yogurt functionality by adding Mentha piprita phenolic extract and evaluation of its quality during cold storage

“…Furthermore, Khelifi et al. ( 2018 ) demonstrated the antibacterial effect of phenolic extract from Lamiaceae plants, specifically Thymus vulgaris L., against St and Lb , as well as an increase in pH accompanied by a decrease in yogurt acidity as a function of the doses of phenolic extract added during both the fermentation and storage periods. Phenolic compounds exert their antibacterial effects through different modes of action: by damaging the cell walls of bacteria, causing the loss of cellular constituents; by blocking the production of cellular energy; or by destroying the genetic material of bacteria (Yang et al., 2008 ).…”

“…All milk batches were inoculated with 3% of a St/Lb leaven mix in a 2:1 ratio. Milk pots were sealed, steamed for 4 h at 45°C, and then refrigerated at 4°C (Arioui et al., 2017 ; Khelifi et al., 2018 ).…”

Effect of the Addition of Selected Herbal Extracts on the Quality Characteristics of Flavored Cream and Butter

“…Comparable results were obtained by Amirdivani and Baba [30], who showed that herbal extracts improved milk fermentation through yogurt bacteria and increased the acidity of yogurts. Khelif et al [31] conducted a study to investigate the effect of thyme extract on LAB growth and concluded that a 2% and 4% addition of thyme extract can be added to yogurts without the risk of deterioration in physicochemical quality or inhibition of lactic bacteria. Bakrm and Salihin [32] found that adding aqueous extract of Ceylon cinnamon and common garlic to goat's milk, cow's milk, and camel's milk had no negative effect on acidification through fermentation.…”