M-BCG Yeast and Mould Broth, Modified

Intended Use

M-BCG Yeast and Mould Broth, Modified is recommended for the detection of fungi in routine analysis of beverages.

Composition**

Final pH ( at 25°C): 4.6±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 7.41 grams in 100 ml distilled water. Heat if necessary to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 10 minutes.

Principle And Interpretation

The number of microbes present in beverages depends on the methods of processing and means of preservation. High microbial populations often indicate poor quality in raw material, unsanitary equipments or opportunity for growth in the food at some stage in the process. Heat processed beverages will be free of aciduric microorganism but may yield low numbers of viable spore forming bacteria when cultured on nonselective media. Bacteria cannot grow in the high acid environment and therefore direct microscopic count for yeast, bacteria or moulds may provide a clue to the conditions of sanitization during processing. Heat resistant spores may be present in low numbers. Because of their slow growth and poor competitive ability, yeast and moulds often manifest themselves on or in foods in which the environment is less favourable for bacterial growth.

M-BCG Yeast and Mould Broth, Modified is also recommended for detecting fungi in routine analysis of beverages using membrane filter technique (1). It contains pancreatic digest of casein and peptic digest of animal tissue as nitrogen source therefore differing in composition of M1130 (M-BCG Yeast and Mould Broth) which contains biopeptone as nitrogen source. Essentially even pancreatic digest of casein and peptic digest of animal tissue serves as rich nutrient source for growth of yeasts and moulds. Yeast extract and Thiamine together provides growth factors and B vitamin to the growing yeast and molds. Dextrose serves as the energy source. Diastase is a mixture of amylolytic enzymes. Bromocresol green acts the pH indicator which is green at acidic pH (4.0) while blue at pH 5.6. Phosphate salts buffers the medium well. The low pH inhibits bacterial growth.

The membrane filter pad is saturated with 2.0 to 2.5 ml broth. Place the membrane filter used for filtration of test sample on the saturated pad and incubate at 30-35°C for 48-72 hours.

Quality Control

Appearance: Cream to light green homogeneous free flowing powder

Colour and Clarity of prepared medium: Green coloured slightly opalescent solution, may contain a slight precipitate.

Reaction: Reaction of 7.41% w/v aqueous solution at 25°C. pH : 4.6±0.2

pH: 4.40-4.80

Cultural Response

M1741: Cultural characteristics observed after an incubation at 30-35°C for 48-72 hours.

*Key: Formerly known as Aspergillus niger ATCC 16404

Storage and Shelf Life

Store below 30°C in tightly closed container and the prepared medium at 2-8°C. Use before expiry date on the label.

Reference

1. MacFaddin J.F., 1985, Media for Isolation –Cultivation-identification-Maintenance of Medical Bacteria,Vol. I, Williams and Wilkins, Baltimore.