This system consists of a square filter with hydrophobic grids printed on the filter to form 1,600 squares for each filter. Food samples are weighed, blended, and enzyme treated before passage through the membrane filter containing the hydrophobic grids by vacuum. The filter is then placed on agar containing a suitable nutrient for growth of the bacteria, yeasts, or molds. The hydrophobic grids prevent colonies from growing further than the square grids; thus all colonies have a square shape. This facilitates counting of the colonies both manually and electronically. This method has been successfully used to make viable cell counts for a variety of foods, including milk, meat, black pepper, flour, peanut butter, mushrooms, rice, fish, shrimp, and oyster (18-20). Other applications of the Isogrid system include determination of total coliforms, fecal coli-forms, Escherichia coli, Salmonella spp., and other microorganisms (21).

Rehydratable nutrients are embedded into a series of films in the Petrifilm (3M Co., St. Paul, Minn.) system. The top layer of the protective cover is lifted and 1 mL of liquid sample introduced to the center of the unit, and the cover is then replaced. A plastic template is placed on the cover to make a round mold. The rehydrated medium with nutrient will support the growth of microorganisms after suitable incubation time and temperature. The colonies can be counted directly in the unit. The unit is about the size and thickness of a plastic credit card, thus providing great savings of space in storage and incubation. Petrifilm units have been developed for total bacterial count, coli-form count, fecal coliform count, yeast and mold counts, and hemorrhagic E. coli 0157:H7. Table 2 shows excellent correlation between Petrifilm and standard plate count method for the food.

Redigel system (RCR Scientific, Inc., Goshen, Ind.) is another convenient viable cell count system. This system consists of sterile nutrients with a pectin gel in a tube. The tube is ready to be used any time and no heat is needed to "melt" agar. A 1-mL food sample is first pipetted into the tube. After mixing, the entire content is poured into a special Petri dish previously coated with calcium. When liquid comes in contact with the calcium, a Ca-pectate gel is formed, and the complex swells to resemble conventional agar. After an appropriate incubation time and temperature, the colonies can be counted exactly like conventional standard plate count method. Besides total count, Redigel also has systems for coliform, fecal coliform, yeast and molds, lactic and bacteria, Staphylococcus aureus, and Salmonella.

The four aforementioned methods have potential as an alternative to the conventional agar pour plate method. Chain and Fung (23) made a comprehensive analysis of all four methods against the conventional method on seven different foods (skinless chicken breast, fresh ground beef, fresh ground pork, packaged whole shelled pecans, raw milk, thyme, and whole wheat flour, 20 samples each) and showed that the new systems and the conventional method were highly comparable and exhibited a high degree of accuracy and agreement (r = 0.95 +). It should be noted that those performing these newer methods need some training and experience before satisfactory results can be obtained consistently. These are good methods if performed under careful operation.

In the direct epifluorescent filter technique (DEFT) method, the liquified sample is first passed through a filter that retains the microorganisms. The filter is then stained with acridine orange, and the slide is observed under ultraviolet microscopy. "Live" cells usually stain orange-red, orange-yellow, or orange-brown, whereas "dead" cells fluoresce green. The slides can be read by the eye, or by a semiautomated counting system marketed by Bio-Foss. A viable cell count can be made in less than an hour. With the use of an image analyzer, an operator can count 50 DEFT slides per hour (24). This method has been used satisfactorily for counting viable cells in milk and other food samples such as fish (25). Recently the Nordic countries used this method for quality assurance of ground beef. Tor-torello and Gendel (26) further developed this procedure by using fluorescent antibodies in conjunction with DEFT to enumerate E. coli 0157:H7 in milk and juice.

Sleeping Sanctuary

Sleeping Sanctuary

Salvation For The Sleep Deprived The Ultimate Guide To Sleeping, Napping, Resting And  Restoring Your Energy. Of the many things that we do just instinctively and do not give much  of a thought to, sleep is probably the most prominent one. Most of us sleep only because we have to. We sleep because we cannot stay awake all 24 hours in the day.

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