Set-yoghurts from goat, cow, and sheep milk from middle lactation period were produced. In fresh yoghurts and after 14 days cold storage the following properties were analysed: hardness, adhesiveness, and extrusion force using instrumental texture analyzer, syneresis using drainage and centrifugal methods and microstructure using scanning electron microscope (SEM). Yoghurt from goat milk was characterized by lower hardness, adhesiveness, extrusion forces, and higher susceptibility to syneresis than yoghurts from cow and sheep milk. Microstructure of goat milk yoghurt was more delicate in comparison with microstructure of cow and sheep milk yoghurt. The composition and/or properties of goat milk for yoghurt production, or processing conditions need to be modified to obtain the proper texture and reduced syneresis in final product.
Elderberries, sea buckthorn, and sloe berries are fruits of wild-grown bushes, valued in folk medicine for their health-promoting properties but still rarely applied in food. The aim of the present study was to produce probiotic yoghurts with a 10% addition of sweetened purees prepared from elderberries (EPY), sea buckthorn (SBPY), and sloe berries (SPY) and to assess their chemical composition, acidity, content of polyphenols and anthocyanins, ferric reducing antioxidant power (FRAP) and antiradical power (ARP), level of starter microbiota, concentration of acetaldehyde and diacetyl, syneresis, instrumentally measured color and texture parameters, and sensory acceptance. The results were compared to those obtained for plain probiotic yoghurt (PPY) and the changes tracked during 1 month of cold storage at 2 week intervals. The addition of elderberry and sloe berries significantly increased the antioxidant capacity of probiotic yoghurts, probably due to a high content of polyphenols, especially anthocyanins. However, anthocyanins were more stable in the EPY when compared to the SPY. All yoghurt treatments were characterized by good sensory quality and viability of starter microorganisms, including probiotic strains during cold storage. Elderberries promoted the evolution of diacetyl in yoghurts during storage and, together with sloe berries, produced increased syneresis and the greatest changes in color profile compared to PPY.
The objective of this study was to determine the effect of concentration degree (1.5-fold, 2-fold, and 2.5-fold [v/v]) of ultrafiltrated goat milk on instrumental texture, syneresis, and microstructure of set-yoghurt. The milk for control yoghurt was non-concentrated. The concentration of goat milk by ultrafiltration caused an increase in the hardness, the adhesiveness, the extrusion force of yoghurt, and a reduction in the syneresis. The microstructure of yoghurts from ultrafiltrated milk showed a compact protein matrix, a small amount of void spaces, and large casein micelles in comparison to the microstructure of yoghurts from non-concentrated milk. The best texture and the smallest syneresis of goat milk yoghurts could be obtained at 1.5-or 2-fold [v/v] goat milk concentration. Yoghurt from 2.5-fold concentrated milk was characterized by a too hard and compact structure with a consistency typical for cream cheese, not yoghurt.
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