Question

Compare the ph of the milk sample and the ph at which the casein solid forms.

Answer 1

comapre the pH of the milk sample :

Milk contains a large number of weak acid or weak base in its salt. so, it behaves as a buffer solution. fresh cow milk has a pH of between 6.7 and 6.5. therefore, it is silghtly acidic. Values higher than 6.7 denote of mastitic milk, while values lower than 6.5 denote the presence of bacterial deterioration. As milk is buffer solution. considerable acid development may occur before the pH changes. pH value lower than 6.5 therefore indicates that considerable acid development has taken place. this is normally due to the bacterial activity.

                       the pH of milk from 6.75 in the first day reduced to 4.8 in the fourth day. this means the acidity of the milk increases from the first day to fourth day. the milk has a high acidity in the fourth day because of the presence of the bacteria that converts the sugars in the milk into acid.

the pH at which the casein soid forms:

                           the effect of pH, milk concentration, heating temperature and heating time on the dissociation of casein from micelles in reconstituted skim milk was investigated. for the 10% total solids milk samples, low levels of casein were rendered soluble at pH below 6.7 regardless of heating temperature , whereas increasing levels of casein were solubilized as at pH was increased from 6.7 to 7.1. the quantity of soluble casein increased with temperature to a maximum dissociation at about 60- 80^oC, decreased as the temperature raised to 100 degree celsius. As the milk was concentrated , a higher level of dissociation of casein, particularly k-casein , was observed at lower pH and at higher temperatures, particularly above 80^oC.

    For casein, the IEP is approximately 4.6 and it is the pH value at which acid casein is precipitated. In milk, which has about 6.6, the casein micelles have a net negative charge and are quite stable.