Raka-Ray Agar

Casein enzymic hydrolysate, liver concentrate, yeast extract provide carbon, nitrogen, amino acids, minerals, vitamins, trace elements and other essential nutrients for growth. Potassium aspartate and potassium glutamate are additional sources of amino acids. Maltose is to detect lactobacilli, which cannot utilize glucose as a carbon source and fructose is the carbon source of Lactobacillus fructivorans. Glucose is needed as the fermentative energy source for the Pediococci. Sorbitan mono-oleate act as a stimulant for lactic acid bacteria in general. Also, N-acetyl glucosamine, liver concentrate yeast extract and betaine hydrochloride are used as growth stimulating agents. Diammonium hydrogen-citrate and Monopotassium phosphate are the buffering agents while Magnesium and Manganese are important trace elements for Lactobacillaceae. The addition of phenylethanol inhibits Gram-negative organisms, while amphotericin B and cycloheximide inhibits growth of yeasts and molds.

Raka-Ray Agar is recommended for selective isolation of lactic acid bacteria encountered in beer and the brewing process.

Raka-Ray Agar was formulated by Saha, Sondag and Middlekauff to monitor the brewing process and analyze it for a wide range of bacteria. The media is found to be superior to several other media for the cultivation of Lactobacilli and Pediococci. It also suppresses the growth of non-lactic acid facultative bacteria that are often associated with lactic beer spoilage.

We offer two media types: the superior granulated GranuCult^® and the cost-efficient powdered NutriSelect^® culture media, depending on your needs.
The designations basic, plus, or prime are added to indicate the quality control level, from basic quality control to standard QC plus to prime for full regulatory compliance.

Suspend 38.5 g in 500 ml of distilled water. Bring to the boil and dissolve the medium completely. Distribute into tubes or bottles and sterilize by autoclaving at 121°C for 15 minutes. Cool to 50-55°C and add contents of 1vial of lactic acid bacteria selective supplement (Cat. No. 14121). Add 3.5 ml of Cycloheximide solution (Cat. No. 18079). Mix well and pour into sterile petri dishes or dispense as desired.

GRANUCULT is a registered trademark of Merck KGaA, Darmstadt, Germany

NutriSelect is a registered trademark of Merck KGaA, Darmstadt, Germany