Food Structure


This study combines an enzyme/surfactant treatment with centrifugal ion and prefiltration to solubilize food constituents in a dairy product containing listeria monocytogenes, remove the constituents by a second filtration and examine the isolated bacteria under the scanning electron microscope. Treatment of an ice cream mix with a combined 2% (w/w} trypsin and 2% (w/w) Tween 80 so lution for 20 minutes at 35 °C resulted i n proteolysis of the dairy mix without lysing the bacteria. Centrifugation at 4300 x g for 20 minutes at 5°C concentrated the bacteria in the form of a pellet which was subsequently purified through a pref ilter system prior to a final filtration through a polycarbonate filter with 0. 4 ~m pores. The bacteria on the filter were fixed in a glutaraldehyde so lution, postfixed with osmium tetroxide, dehydrated in an ethanol series, impregnated with hexamethy ldi si lizane and airdried. This procedure made it possible to retrieve sufficient concentrations of purified bacteria on the filter for examination in the SEM.

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