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Thermo Scentific

Dehydrated Culture Media


Code: CM0657

A medium for the isolation and enumeration of spoilage organisms of citrus products.

Typical Formula*




Yeast extract


Orange serum (equivalent solids)




Di-potassium phosphate




pH 5.5 ± 0.2 @ 25°C

* Adjusted as required to meet performance standards 

Suspend 37g in 1 litre of distilled water and bring gently to the boil to dissolve completely. Dispense into final containers and sterilise by autoclaving at 121°C for 15 minutes.

Orange Serum Agar was developed specifically for the isolation and enumeration of micro-organisms that are capable of surviving in citrus products1. The low pH of these products limits the growth of micro-organisms to those capable of tolerating the acidic environment.

Organisms known to grow in single strength and concentrated citrus juices are lactic acid and acetic acid bacteria, yeasts and moulds2. Of this group of organisms lactic acid bacteria have been mainly implicated as the cause of spoilage and these have been identified as Lactobacillus plantarum, Lactobacillus brevis, Leuconostoc mesenteroides and Leuconostoc dextranicum3.

In comparative studies carried out by Murdock et al.4 Orange Serum Agar was found to be a superior medium when compared to other media used for the total count and detection of spoilage organisms.

1. Prepare the medium as directed.
2. Add 1ml of the test sample to a sterile Petri dish.
3. Add approximately 20ml of cooled medium (50°C) to each plate and mix according to the plate count method5.
4. Incubate at 30°C and examine daily for up to seven days.
5. Report as number of colony-forming units per ml of test material.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at 2-8°C.

Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Straw-orange coloured gel

Quality control

Positive controls:

Expected results

Lactobacillus fermentum ATCC® 9338 *

Good growth; cream coloured colonies

Saccharomyces cerevisiae ATCC® 9763 *

Good growth; cream coloured colonies

Negative control:


Uninoculated medium

No change

* This organism is available as a Culti-Loop®

Do not overheat the medium.

1. Hays G. L. (1951) Proc. Florida State Hort. Soc., 64th Ann. Meeting.
2. Murdock D. I. and Brokaw C. H. (1958) Food Tech. 12. 573-576.
3. Hays G. L. and Riester D. W. (1952) Food Tech. 6. 386-389.
4. Murdock D. I., Folinazzo J. F. and Troy V. S. (1952) Food Tech. 6. 181-185.
5. American Public Health Association (1992) Compendium of Methods for the Microbiological Examination of Foods 3rd Edtn. APHA Inc. Washington DC.

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