Protein degradation in bovine milk caused byStreptococcus agalactiae

Abstract

Streptococcus (Str.) agalactiae is 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 this in vitro study was to evaluate protein degradation mainly caused by exogenous proteases originating from naturally occurring Str. agalactiae. The samples were incubated at 37°C to imitate degradation caused by the bacteria in the udder. Protein degradation caused by different strains of Str. agalactiae was also investigated. Protein degradation was observed to occur when Str. agalactiae was 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 with Str. agalactiae in 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.

Effect of somatic cell count on composition and hygiene indicators of bulk tank milk

“…These results and the results obtained in the present study differ in relation to the correlation between SCC and fat (r = 0.2217) and are similar in relation to SCC and protein (r = 0.2346). The increased content of milk protein that occurred in high SCC milk can be explained by the change in milk composition in response to inflammation in the mammary gland, and consequently the increase in concentration of serum proteins in milk (ÅKERSTEDT et al, 2012). Machado et al (2000) reported that milk from tanks with SCC > 1,500,000 cells/mL presented higher content of fat than milk from herds with SCC < 1,000,000 cells/mL, and herds with SCC < 500,000 cells/mL presented higher content of protein than herds with SCC > 500,000 cells/mL.…”

“…Due to the increase of somatic cell count (SCC) of milk in response to intramammary infection, milk quality is reduced because of changes in milk composition, such as increased concentration of free fatty acids and serum proteins, decreased casein and lactose content, and changes in milk mineral contents (ÅKERSTEDT et al, 2012). These changes occur in response to the action of inflammation mediators and the activity of enzymes and toxins synthetized by mastitis pathogens (BRANDT et al, 2010).…”

Efeito da mastite bovina sobre a composição e indicadores de higiene em leite de tanque

“…Estas perdas são devidas principalmente ao menor rendimento de fabricação de derivados lácteos pela alteração na composição do leite e pela menor vida de prateleira do leite e seus derivados (ÅKERSTEDT et al, 2012;ARCHER et al, 2013). Para o produtor de leite, as perdas se devem à redução da produção e ao descarte do leite, ao trabalho extra para tratamento e custo de aplicação de antibióticos e ao aumento do risco de doenças subsequentes, além de ser uma das principais causas de descarte de vacas em rebanhos leiteiros (GROENENDAAL et al, 2004;HOGEVEEN et al, 2011).…”

“…Nos casos de mastite, as principais alterações no leite são a elevação da quantidade de ácidos graxos livres, a diminuição do teor de caseína do leite e aumento do teor de proteínas do soro (ÅKERSTEDT et al, 2012), assim como redução da concentração de lactose, alteração de teores de sódio, cloro, potássio e cálcio e aumento do pH. Estas alterações são causadas pelos mediadores químicos da inflamação e pela atividade das enzimas e toxinas bacterianas no leite e podem ocorrer em diferentes intensidades dependendo da forma de manifestação e duração da inflamação da glândula mamária (BRANDT et al, 2010).…”

“…Com o aumento da contagem de células somáticas (CCS) em resposta à infecção da glândula mamária por micro-organismos causadores da mastite, são observadas diversas alterações na composição do leite, tais como o aumento da quantidade de ácidos graxos livres, a diminuição do teor de caseína e a elevação do teor de proteínas séricas (ÅKERSTEDT et al, 2012), além da redução do teor de lactose e alteração de teores de minerais do leite. Estas alterações são devidas à ação de mediadores da inflamação e à atividade das enzimas e toxinas sintetizadas pelos patógenos da mastite (BRANDT et al, 2010).…”