Similarly, other ingredients like tryptone, yeast extract, and dextrose are the source of amino acid, vitamin B complex, and carbon.įollowing inoculation and incubation of the culture agar plate, proteolytic bacteria will form a zone of proteolysis, demonstrating a transparent area surrounding the bacterial growth. The opacity of the medium is due to the deflection of light instead of transmitting it. Skim milk powder in a medium acts as a casein source and gives the medium opacity and color. As significant ingredients, the medium comprises skim milk powder, tryptone, yeast extract, dextrose, and agar. Milk agar is used to demonstrate such activity in the laboratory. Some microbiomes can degrade such proteins (casein) by producing extracellular enzymes known as proteinase (caseinase). Microorganisms cannot directly utilize large protein molecules. Quality control Principle of Casein Hydrolysis Test.The proteinase cleaves the peptide (CO-NH ) bond of adjacent amino acids by introducing water molecules to release polypeptides and amino acids.Ĭasein→small chain of amino acids, dipeptides, and polypeptides in the presence of caseinase and water molecules. These reactions are catalyzed by proteinases (caseinase) and peptidase enzymes. Therefore, it must undergo step-by-step degradation into peptides and a small chain of amino acids for assimilation. The microorganism cannot uptake casein as it is a large molecule. This results in a transparent zone around the growth Thus, the test performed to detect the breakdown of casein is known as the casein hydrolysis test.Ĭasein, a dominant milk protein, is a macromolecule comprising amino acid subunits linked together by a CO-NH bond. Therefore, the casein hydrolysis test is one of the important test that helps to identify microorganisms based on detecting exoenzyme (caseinase) activity.Ĭasein hydrolysis is the degradation of casein protein present in an opaque milk agar due to metabolic activity of organism into soluble end products like amino acids, peptides, etc. As enzymes catalyze all physiological reactions, detecting the enzyme produced is an essential tool for species identification and differentiation. The physiological reactions of microorganisms are crucial in species identification and differentiation.
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