Dehydrated culture media
Raka-Ray Agar Base
Selective medium for the isolation of lactic acid bacteria in beer and beer fermentation.
- Cat. No.
- LC-1061
- Category
- Dehydrated culture media
- Format
- 500 g
- Storage
- 2 to 25 °C
- Minimum guaranteed shelf life
- 15 months
Raka-Ray Agar Base is a selective medium for the isolation of lactic acid bacteria in beer and brewing processes. It yields very good results in the detection of lactobacilli in the fermentation processes of beer.
Key features
Applications
Selective isolation of lactic acid bacteria.
Industry
Alcoholic beverages.
Preparation
77.2 g in one liter of distilled water, add 10 mL of sorbitan monooleate; sterilize in autoclave at 121 °C for 15 minutes, then add 3 g of phenylethanol.
Principles and uses
These organisms can change the organoleptic characteristics of the beer through their metabolites. Detection is complicated because of the nutritional and environmental requirements of these organisms. For these reasons, several formulations have been described to optimize the medium and obtain good growth.
Higher counts of lactobacilli in comparative tests have been obtained with this medium because it contains growth nutrients and stimulants such as liver extract, yeast extract, tryptone, N-acetylglucosamine and sorbitan monooleate. Maltose and fructose are added as sources of carbohydrates when certain lactobacilli can't use glucose. Selectivity is obtained by adding 3 g/L of phenylethanol, to inhibit Gram-negative bacteria, and cycloheximide to inhibit yeasts. Sulfate salts provide inorganic ions. Betaine hydrochloride is used as a growth stimulating agent. Diammonium hydrogen citrate and potassium phosphate are buffering agents. Potassium aspartate and potassium glutamate are additional sources of amino acids. Bacteriological agar is the solidifying agent.
Lactobacillus fermentans grow as white-cream colonies. If the number of colonies on each plate exceeds 300, dilute the sample 1:10 in sterile saline and re-test.
Technical specifications
| Solubility | Without residues |
|---|---|
| Appearance | Fine powder |
| Color of the dehydrated medium | Beige |
| Color of the prepared medium | Toasted |
| Final pH (25 °C) | 5.4 ± 0.2 |
| Amount per litre | 77.2 g |
| Storage | 2 to 25 °C |
Formula
| Ingredient | g/L |
|---|---|
| Glucose | 5 |
| Bacteriological agar | 17 |
| Cycloheximide | 0.007 |
| Magnesium sulfate heptahydrate | 2 |
| Maltose | 10 |
| Potassium phosphate | 2 |
| Tryptone | 20 |
| Yeast extract | 5 |
| Fructose | 5 |
| Manganese sulfate tetrahydrate | 0.66 |
| Potassium aspartate | 2.5 |
| Potassium glutamate | 2.5 |
| Betaine hydrochloride | 2 |
| Diammonium hydrogen citrate | 2 |
| Liver extract | 1 |
| N-acetylglucosamine | 0.5 |
Preparation and use
Preparation
Suspend 77.2 grams of the medium in one liter of distilled water. Add 10 mL of sorbitan monooleate. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 °C for 15 minutes. DO NOT OVERHEAT. Cool to 45-50 °C and aseptically add 3 grams of phenylethanol. Mix well and dispense into plates.
Instructions for use
Overlay technique:
- Inoculate 0.1 mL of the sample onto well-dried plates containing 15-20 mL of Raka-Ray Agar.
- Spread over the surface of the medium using a sterile glass rod.
- Overlay the surface with 4 mL of the molten sterilized medium cooled to 50 °C.
- Incubate plates at 25-30 °C for 4-7 days.
Depending on the type of microorganisms, incubate or not in anaerobiosis.
Quality control
Microbiological test
Incubation conditions: 25-30 °C / 4-7 days.
| Microorganism | Specification |
|---|---|
| Escherichia coliATCC 25922 | Total inhibition |
| Pediococcus acidilacticiATCC 8042 | Good growth |
| Lactobacillus fermentumATCC 9338 | Good growth |
| Saccharomyces cerevisiaeATCC 9763 | Total inhibition |
Bibliography
- Methods of Analysis of the ASBC (1976) 7th Edition, The Society, St. Paul, Mn. USA.
- European Brewing Convention, EBC Analytica Microbiologica: Part II J. Inst. Brewing (1981) 87.303-321.
What you receive
The product
Shipped under controlled temperature when the product requires it.
Lot certificate
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Tracked shipment
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