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This study demonstrated that vibration (with a constant frequency, i.e. 30 Hz, acceleration of 1 g, exposure time of 60 min and variable container filling, i.e. 50, 80 and 100%) affected an increase in milk acidity and produced unfavorable changes in its components. The dynamics of these changes were inversely proportional to the degree of milk container filling. The storage stability of the raw material was limited, to a statistically significant extent, by the temperature of incubation and the degree of milk container filling during vibration. The properties examined were observed to change with higher dynamics during storage of the raw material at a temp. of 8°C, and the greatest changes in both components and properties of milk were in the samples subjected to vibration with 50% filling of the container.
This study addressed a comparative analysis of selected characteristics of technological usability of milk of Jersey (Je) and Holstein-Friesian (hf) cows. Milk of Je cows was characterized by a higher content of total nitrogen and casein nitrogen as compared to that of hf cows, however, the casein number was similar for both breeds of cows. Heat stability of the milk of Je cows was twofold higher, whereas its rennet coagulation time was shorter (by 13%) as compared to the milk of hf cows. Ethanol stability of the analyzed milk samples of both cow breeds was at a similar level. Milk originating from cows of Je breed was characterized by a higher content of fat, occurring in the form of fat globules greater in size, and a higher rate of creaming, as compared to milk of hf cows.
Przedmiotem badań było porównanie składu kwasów tłuszczowych, ze szczególnym uwzględnieniem zawartości sprzężonego kwasu linolowego (cis9trans11 C18:2) oraz izomerów trans kwasu C18:1 i C18:2, w mleku oraz wyprodukowanych z niego kefirach i jogurtach. Analizie poddano mleko surowe, mleko znormalizowane oraz wyprodukowane z niego kefiry i jogurty. Oznaczenia przeprowadzono metodą GC w 100-metrowej kolumnie kapilarnej z fazą CP Sil 88. Zastosowany w doświadczeniu proces technologiczny produkcji kefirów i jogurtów nie wpłynął na profil kwasów tłuszczowych ocenianych mlecznych napojów fermentowanych. Skład kwasów tłuszczowych tłuszczu kefiru i jogurtu był zbliżony do składu kwasów tłuszczowych tłuszczu mleka. Zawartość sprzężonego kwasu linolowego cis9trans11 C18:2 (CLA) oraz izomerów trans kwasu C18:1 i C18:2 w badanych napojach fermentowanych zależała od ich koncentracji w surowcu, z którego zostały wytworzone.
The aim of the present study was to determine the effects of cold storage (temp. 4 and 8°C) on some physicochemical properties and technological suitability of raw milk subjected to vertical vibration at various frequencies (10, 30 and 60 Hz). An analysis of the results showed that vibration increased milk acidity and negatively affected milk components. The process caused, among others, an increase in the levels of ionic calcium and free fatty acids, as well as protein degradation (an increase in the formalin number), which deteriorated the technological quality of milk (a decrease in thermal stability and ethanol stability, a shorter rennet coagulation time). The degree of these changes corresponded to an increase in vibrational frequency. Intensive lipolytic and proteolytic processes and enhanced acidity were observed during cold storage of raw milk subjected to vibration. This had a negative effect on the technological suitability of milk. The changes were less significant in the case of deep chilling (4°C).
The ethanol-influenced changes in proteins and some mineral compounds of milk were examined. Despite apparent phasing (induction and post-induction phases), the ethanol coagulation of milk was found to be a continuous process, lasting until 75% of proteins was coagulated and about 20% of proteins was changed into proteozo-peptone and non-protein nitrogen. It was shown that as2-casein and ß-lactoglobulin were more resistant to alcohol than heating. The solubility of mineral compounds of milk was found to decrease upon the alcohol addition and the Ca/P weight ratio was indicative of variability in the form of salts being precipitated.
The research was aimed at determining the effect of high-pressure homogenization (100 MPa) on the stability of proteins and equilibrium of mineral salts in skim milk and milk standardized to fat content of 2% and 4%. High-pressure homogenization of skim milk evoked a slight increase in the content of protein compounds sedimenting during ultracentrifugation and in a degree of their hydratation. In turn, homogenization of milk with the standardized fat content affected a decrease in the content of proteins in milk plasma as well as in the quantity of sedimenting proteins and in the degree of their hydrations, both observed to intensify along with a higher fat content. In addition, the study demonstrated partial denaturation of whey proteins, an increase in the level of soluble forms of calcium and phosphorus salts, as well as a decrease in heat stability and time of rennet coagulation upon high-pressure homogenization. The changes were observed to intensify along with an increasing content of fat in milk.
The effect of high-pressure (100 MPa) homogenization on some properties of the emulsion phase and colloidal phase of milk standardized to 2% fat or 4% fat were determined in the study. High-pressure homogenization caused a decrease in the size of fat globules and an increase in the level of protein compounds bound to the milk fat fraction, dependent upon the fat content of milk. The process resulted in an increase in the amount of ultracentrifuged sediment, in the level of sedimenting plasma proteins not bound to the milk fat fraction, and in the solubility of calcium salts and phosphorus salts, as well as a decrease in their levels in the colloidal form, related to the fat content of milk. High-pressure homogenization led to slight changes in active acidity and conductivity (increase), as well as to a substantial decrease in heat stability (max. 42.4%) and a shorter rennet coagulation time (max. 34.5%), directly proportional to fat concentration in milk.
The hygienic quality and physicochemical properties of raw milk from Holstein-Friesian and Jersey cows were determined in the study. It was found that the total bacterial count and the somatic cell count in milk samples were within the threshold limit values specified by relevant legal regulations. Milk from Jersey cows contained much higher levels of dry matter, which resulted primarily from higher concentrations of protein compounds (by approx. 19%), both casein and whey proteins, as well as fat (by approx. 50%), as compared with milk from Holstein-Friesians. The levels of all analysed calcium forms (total, colloidal, soluble, ionic) were higher in milk from Jersey cows than in milk from Holstein-Friesian cows. The characteristics of the dispersion state of fat globules showed that their average diameters were greater (by approx. 24%) in milk from Jersey cows, in comparison with milk from Holstein-Friesians. The levels of lactose and milk properties, i.e. acidity, density, conductivity and freezing temperature, were similar in both cow breeds.
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