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Count semiviable bacteria in cheese.

Wageningen University It is based in the Dutch city of Wageningen. Wageningen University
Wageningen University was established in 1918 and was the successor of the Agricultural School founded in 1876.
 researcher Christine Bunthof has developed a direct method for counting bacteria in dairy products. The technique not only distinguishes viable and nonviable nonviable /non·vi·a·ble/ (-vi´ah-b'l) not capable of living.

Not capable of living or developing independently. Used especially of an embryo or fetus.
 bacteria, but also semiviable bacteria. These are too weak to divide, but they still exhibit some activity.

Semiviable bacteria play an important role in cheese ripening ripening

said of meat. See curing.
 by influencing the product's taste. With the new counting method, developers of probiotic pro·bi·ot·ic
A dietary supplement containing live bacteria or yeast that supplements normal gastrointestinal flora, given especially after depletion of flora caused by infection or ingestion of an antibiotic drug.
 dairy products can also investigate how active the added bacteria are when they enter the gastrointestinal tract gastrointestinal tract
The part of the digestive system consisting of the stomach, small intestine, and large intestine.

Gastrointestinal tract 

This new counting technique also is applicable to yogurt. Some bacteria from these and other products do not survive the acidic gastric juices and the bile in the small intestine small intestine

Long, narrow, convoluted tube in which most digestion takes place. It extends 22–25 ft (6.7–7.6 m), from the stomach to the large intestine.
. Using this new method, producers can test how well bacteria reach the intestines in an active form.

The microbiologist from Wageningen stained the bacteria with two fluorescent substances. One substance ensures that the bacteria emit a green color if they are active. The substance itself is not fluorescent, but it is converted by bacterial enzymes into a green fluorescent dye. The second substance stains bacteria with a damaged membrane. This substance emits a red color, but only when it is bound to the bacteria's DNA DNA: see nucleic acid.
 or deoxyribonucleic acid

One of two types of nucleic acid (the other is RNA); a complex organic compound found in all living cells and many viruses. It is the chemical substance of genes.

The process distinguishes viable from nonviable types of bacteria. It also detects semiviable bacteria since, although these can no longer divide, they are still active and emit a green color. Only nonviable bacteria emit red. Investigators use a flow cytometer to count the bacteria. In this device, the bacteria are transported one-by-one past a laser which illuminates the bacteria. A detector counts the number of red and green bacteria.

Since time immemorial, the dairy industry has always counted bacteria that can still divide. When cultured on a nutrient medium, these bacteria form visible colonies. However, this old method fails to detect semiviable bacteria, since active bacteria that do not multiply remain invisible. Yet this intermediate group constitutes a considerable proportion of the active bacteria found in ripening cheese.

Further information. Christine Bunthof, Laboratory of Food Microbiology, Wageningen University, Postbus 8129, 6700 EV Wageningen, The Netherlands; phone: +31 (0)317 482887; fax: +31 (0)317 483584; email:
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Publication:Emerging Food R&D Report
Date:Jan 1, 2003
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