Milk is an excellent source of well-balanced nutrients and shows, also, biological activity that influence digestion, metabolic responses to absorbed nutrients and disease resistance. In this paper, 3 yogurt samples were made from a mixture of goat’s and cow’s milk: 3: 1; 1: 1; 1: 3. The quality characteristics were evaluated by means of physico-chemical indices (acidity, pH, syneresis, viscosity, total dry matter, fat content, protein content, aw, ash content), microbiological (total number of microorganisms and yeasts) and organoleptics. For the yogurt made from milk mixture in a ratio of 1: 1, higher quality indices were observed than the other samples, namely: an increase in the number of lactic acid bacteria more intense (0.98 ± 0.024 μ), respectively a higher lactic acid content (63,398 ± 0.022 g · dm-3), lowering of the pH value (6.75 ± 0.03-4.55 ± 0.01) and more special organoleptic characteristics: fine and homogeneous curd, without gas bubbles, pleasant taste and smell, without syneresis. This yogurt sample also showed the best results during the storage period (1-15 days).
The yogurt was obtained from a combination of 50% goat's milk and 50% cow's milk with the inclusion of scald fruits of aronia (Aronia melanocarpa), raspberries (Rubus idaeus), strawberry (Fragaria xanassa). Physico-chemical and microbiological indices were determined, according to standard methods, after manufacture and storage, after 1, 5, 10, 15 days. Compared to other samples, yogurt with aronia showed the best values of the dynamics specific to the development of microorganisms: 2.93.107 cfu/ml; the growth rate of lactic acid bacteria at fermentation 0.95 μ; physico-chemical indices: titratable acidity 85 ± 0.078⁰T, pH 4.28 ± 0.002, water activity 0.875 ± 0.025; total dry matter 18.45 ± 0.31%, viscosity 2500 ± 0.023 mPa s, ash content 0.89 ± 0.10% and the optical density 2.531 ± 0.054 nm. Yeasts and molds were not detected in any of the samples. From a physico-chemical point of view, in storage, in all fruit yogurt samples the titratable acidity showed increasing values, pH remaining in the range of permissible values. In storage fruits formed an association to control the microbiological risk and stability of yogurt. Fruit yogurt shows a synergism with Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactococcus lactis subsp lactis biovar diacetilactis. The overall Pearson coefficient (Pc = f(pH and MC) for all fruit yogurt samples is -0.95066.
The objective of this study was to investigate the impact of adding aronia (Aronia melenocarpa), raspberry (Rubus idaeus), and strawberry (Fragaria xananassa) in the form of 10% puree to a mixture of cow's and goat's milk in order to reduce the risk of spoilage caused by activity of Bacillus cereus in yoghurt made from a mixture of cow's and goat's milk. During the fermentation process (360 min.), changes in water activity, pH, moisture content, bacterial growth curve were monitored. The results showed a decrease in water activity, pH, and moisture content. Adding aronia puree to yoghurt yielded the most significant results for water activity modification (0.971-0.868), pH (5.31-4.28), moisture content (85.12-81.55 %), and optical density (0.19-0.34). Also, the investigation of the kinetics of the Bacillus cereus grows indicated that the stationary phase was reached at 360 minutes, resulting in a total population of 5.5·1013 c.f.u./g. Microscopic examination revealed Gram-positive strains of lactic acid bacteria, arranged in chains of varying lengths, in an amount of 139·102 c.f.u./g. Antimicrobial activity showed a zone of inhibition with a diameter of 18.5±0.1 mm in aronia yoghurt, a zone of inhibition with a diameter of 16.2±0.2 mm in raspberry yoghurt and a zone of inhibition with a diameter of 15.2±0.1 mm in strawberry yoghurt compared to classic yoghurt which showed a zone of inhibition with a diameter of 12.1±0.2 mm.
Obiectivele acestui studiu au fost analiza iaurtului procesat din amestec de lapte de capră și vacă (seria I) și lapte de capră (seria II) cu adaos de piure din fructe de aronia (Aronia melanocarpa), zmeură (Rubus idaeus) și căpșuni (Fragaria ananassa). Din punct de vedere fizico-chimic, conținutul de zaharuri în probele de iaurt din lapte de capră cu căpșuni a prezentat cele mai mici valori (2,79±0,01%). La păstrare, cea mai bună evoluție a sinerezei (1,05±0,04-2,01±0,05 ml/100 ml) și a capacității de reținere a apei (66,6±0,02-56,1±0,01 %) s-a observat la iaurtul din lapte de capră și lapte de vacă cu căpșuni. Din punct de vedere cromatic, caracteristicile de culoare cu cele mai înalte valori (85,31±2,75-83,00±3,54) au fost observate la iaurtul din lapte de capră și lapte de vacă cu fructe de aronia. Din punct de vedere organoleptic, iaurtul din lapte de capră și lapte de vacă cu căpșuni a obținut și și-a păstrat cel mai înalt punctaj, având aromă răcoritoare, consistența unui gel vâscos, neted și un gust dulceag.
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