• Proteolytic : break protein
• Saccharolytic : break sugar
• Lipolytic : break lipids

Saccharolytic

• Streptococcus lactis ferments lactose of milk into lactic acid. Other Saccharolytic forms are:

1. Streptococcus cremaris
2. Leuconostoc citrovorum etc. which also produce lactic acid in milk.

• Several species of Lactobacillus are commonly found in milk. They are :

Lactobacillus acidophilus

Lactobacillus bulgaricus

Lactobacillus brevis

Lactobacillus fermentum

Lactobacillus thermophilus etc.

• The main end product is lactic acid in several of the cases but in some of the cases, other acids and alcohol may also be produced.
• Microbacterium lacticum, Micrococcus luteus, Micrococcus varians, Micrococcus freudenreichii are also the bacterial fermenters present in milk.
• Some bacteria ferment milk and produce gas.
• Clostridium butyricum, Candida pseudotrophicalisare some of the organisms which produce gas in the milk, fermenting lactose.

Lipolytic

• Several microorganisms which are Lipolytic enter into the milk thorough various sources
• g.: Enterobacter aerogenes cause ropiness in milk, in which case, the milk becomes viscous (slimy) or stringy and produce a gummy substance in the milk.
• Some organisms split the fat in milk & produce glycerol and fatty acid resulting in a rancid taste and soul milk.

Pseudomonas fluorescens

Candida lipolytica

• Penicillium spp.are some of the microorganisms responsible for such action.
• Besides this some bacteria like Serratia marcescens produce red coloration, Pseudomonas synxanthia produce yellow coloration.
• Pseudomonas syncyanea produce blue coloration in milk.

Proteolytic

• Milk is coagulated or curdled without acid production when the casein contained is coagulated.
• This is brought about by bacteria like Bacillus subtilis, Bacillus cereus var. mycoidea, Pseudomonas viscosa and Streptococcus lignaefaciens.
• When milk is stored for longer period, certain characteristic bacteria multiply depending upon the condition of storage.
• If stored at low temperature psychrophilic bacteria multiply whereas at higher temperature (above 60⁰C) thermophilic bacteria multiply and spoil the milk.
• These bacteria survive pasteurization so they are harmful.

Bacillus stearothermophilus

Mycobacterium lacticum

Micrococcus luteus

• Streptococcus thermophilus are some of the microorganisms found to cause severe damage at higher storage temperature.
• Several pathogenic microorganisms may spread through milk and cause disease outbreaks.
• Pathogenic organism from infected cow may pass to milk and through milk to man or calves. Some examples of the disease that spread through milk are:

Tuberculosis               – Mycobacterium bovis

Brucellosis                  – Brucella abortus

1. fever – Coxialla burnetti

Typhoid fever – Salmonella typhii

• Beside these some humane pathogens may find their way to milk, through which, they spread from one place to another place and from one individual to another individual.
• Typhoid, Depthera, Dysentery are some examples of these disease.