Streptococcus(Str.)agalactiaeis a contagious mastitis bacterium, often associated with cases of subclinical mastitis. Different mastitis bacteria have been evaluated previously from a diagnostic point of view, but there is a lack of knowledge concerning their effect on milk composition. Protein composition is important in achieving optimal yield and texture when milk is processed to fermented products, such as cheese and yoghurt, and is thus of great economic value. The aim of thisin vitrostudy was to evaluate protein degradation mainly caused by exogenous proteases originating from naturally occurringStr. agalactiae. The samples were incubated at 37°C to imitate degradation caused by the bacteria in the udder. Protein degradation caused by different strains ofStr. agalactiaewas also investigated. Protein degradation was observed to occur whenStr. agalactiaewas added to milk, but there were variations between strains of the bacteria. Caseins, the most economically important proteins in milk, were degraded up to 75% in milk inoculated withStr. agalactiaein relation to sterile ultra-high temperature (UHT) milk, used as control milk. The major whey proteins, α-lactalbumin and β-lactoglobulin, were degraded up to 21% in relation to the sterile control milk. These results suggest that different mastitis bacteria but also different strains of mastitis bacteria should be evaluated from a milk quality perspective to gain knowledge about their ability to degrade the economically important proteins in milk.

The demand for vegetable protein substitutes for animal protein is growing. Soymilk, the water extract of soaked and ground soybeans is a popular alternative for bovine milk. Soymilk was tested with several non‐animal derived stabilizers to produce fermented soy‐gels and found agar‐agar provides promising organoleptic properties in fermented soy‐gels. The sensory analysis proved that Bifidobacteria (BB) used together with Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus as starter culture bacteria (SCB) gives better (P<0.05) sensory properties. Physicochemical properties were evaluated for gels fermented with SCB and BB. Results indicated, upon storage at 4°C, pH reduced (P<0.05) and viscosity increased (P<0.05). Both titratable acidity and syneresis were initially decreased and increased after the 10^th day of storage. After seven days, the viability of BB in fermented soy‐gel was higher (P<0.05) than in a regular bovine milk set‐gel, proving the feasibility of using as a promising probiotic carrier vegan food.

The objectives of this study were to establish the proteolytic effects of Staphylococcus aureus during mastitis on economically important milk proteins. Concentrations of milk proteins were determined by capillary electrophoresis in an experimental model using a field strain of S. aureus. The pathogen was inoculated into bacteria-free control milk to imitate proteolysis caused by the pathogen in the mammary gland between milkings. Milk content of caseins (CN) α(S1), α(S2), κ, β(A1), and β(A2) and whey proteins α-lactalbumin and β-lactoglobulin were analyzed initially and after 6 h of incubation. After 6 h, the overall CN content was significantly reduced (21%) in milk inoculated with S. aureus compared with the bacteria-free control milk. S. aureus significantly lowered concentration of α(S1)-CN (2.5%), β(A1)-CN (3%), and β(A2)-CN (5%). S. aureus also hydrolyzed κ-CN into para-κ-CN, with significant reduction of κ-CN (7.4%) as a consequence.

The objective of the studies reported in this research communication was to investigate differences in composition and enzymatic activities in bulk milk samples provided from Swedish dairy farms with different management systems, i.e. automated (AMS) and conventional milking systems (CMS). A bulk milk sample was collected from each of 104 dairy farms, 51 using AMS and 53 using CMS, located in the same geographical region. Sampling took place within two consecutive days during the indoor period (October). Milk samples were analysed for contents of total fat and protein, free fatty acids (FFA), caseins and whey proteins, somatic cell count (SCC), pH, plasmin and plasminogen derived activities, and total proteolysis. Our results showed a lower protein content and higher SCC in bulk milk from AMS herds compared with milk from CMS herds. Plasmin, plasminogen and total plasmin/ plasminogen derived activities were lower in milk from AMS herds but despite this, total casein and the ß-casein fraction as % of total protein were lower in milk from AMS herds than in milk from herds using CMS. Total proteolysis was higher in milk from AMS herds, suggesting that other proteases than plasmin, e.g. cellular and bacterial proteases, contributed to the degradation of casein. This was supported by a positive correlation between SCC and total proteolysis (P < 0·01), as well as a negative correlation between total proteolysis and ß-casein fraction (P < 0·05). In conclusion, comparing the quality of bulk milk from commercial dairy herds using AMS and CMS, respectively, several differences were observed, suggesting a significant effect from management system.

High frequency of Swedish Landrace goats are the carriers of a mutation, where the affected goats are not able to produce α-casein (α-CN) in the milk. As a consequence the lack of this protein is connected to lower cheese yield. The aim of this study was thus to determine the relationship between the α-CN content and coagulation properties of milk from Swedish Landrace goats. Milk samples from 62 dairy goats from two herds were analysed. As many as 44% goats showed low or no production of α_S1-CN. Only 24% of the investigated goats showed high production of this protein. The coagulation properties of milk from the dairy goats were clearly influenced by the concentration of α_S1-CN. The milk from low level α_S1-CN animals resulted in 15% longer coagulation time and 60% weaker gels compared to the gel firmness of the high expressing group. The coagulation time was strongly associated with the pH of the milk (p<0.001), where the milk with low α_S1-CN content had higher pH. Further, goat milk with low levels of α_S1-CN was shown to have significantly lower total protein (p<0.05) compared to milk from high expressing α_S1-CN goats.