：The use of ordinary skim milk powder is undesirable in bacteriological media because of the presence of heat-resistant organisms which give rise to erroneous cultural results. Oxoid Skim Milk Powder is a special bacteriological grade of spray-dried skim milk free from thermophilic organisms.
Reducing Sugars (as lactose monohydrate)
Ether Soluble Extract
Mix the powder to a smooth paste with a small quantity of distilled water, then gradually add more distilled water until a 10% w/v mixture is obtained. This is equivalent to fresh milk, and may be sterilised by autoclaving for 5 minutes at 121°C. Care should be taken not to overheat during sterilisation, otherwise caramelisation will occur. This product may be used alone or as a constituent of more complex bacteriological culture media. A 10% `solution’ of Skim Milk Powder, containing 0.001% of bromo-cresol purple forms a highly satisfactory purple milk which may be employed for the cultivation of dairy organisms or for the differentiation of Clostridium species, etc. Media containing skim milk powder are of particular value for diagnostic cultural tests involving the fermentation of lactose and digestion or coagulation of casein.
This product is not always free from antimicrobial residues. Where antibiotic-free milk powder is specified in a formulation, tests must be carried out to determine if it is satisfactory.