A Colorimetric Sensor of Food Spoilage Based on a Molecularly Imprinted Polymer
Food poisoning is caused by ingesting toxins produced by the activity of food borne microorganisms. These toxins are often relatively heat stable and are capable of surviving the cooking process. Meat spoilage occurs as bacteria begin to grow unchecked at the time of slaughter. One of the markers of meat spoilage is the decarboxylation of free amino acids on and in the meat by enzymes released by spoilage microorganisms. Two of these products, putrescence and cadaverine, are particularly distinctive in odor, and correlate well with surface bacteria counts, and are widely used to evaluate meat freshness by both trained meat inspectors and individual consumers. Another product, histamine, is of interest due to its apparent ability to potentate histamine intoxication, a form of food poisoning associated with the consumption of spoiled fish. Accordingly, there is a need for a robust sensor device which accurately, simply and rapidly detect the presence of biogenic amines in food products.
The Johns Hopkins University Applied Physics Lab has developed molecularly imprinted polymers (MIP), a class of synthetic polymers that may be tailored to selectively detect a particular substance. The molecular imprinting technique involves a polymer, which has been synthesized in the presence of a target molecule, being used to separate a target molecule from other species. The polymers are constructed with ligands to contain cavities which closely match the shapes of various analyte molecules. The analyte molecules are incorporated into a pre-polymeric mixture and allowed to form bonds with the pre-polymer. The mixture is then polymerized with the analyte molecules in place. Once the polymer has formed, the analyte molecules are removed, leaving behind cavities with the analyte molecule's shape. In this way, a particular molecule can be identified since the shape of the cavity is specific to the molecule modeled. This invention is an inexpensive polymer material that indicates meat spoilage through a color change. APL has developed a polymeric sensor which exhibits selective binding affinity for biogenic amine and undergoes a detectable change in absorption or emission of electromagnetic radiation upon exposure to biogenic amine. Upon contact with biogenic amines such as putrescence (1,4-diaminopentane), cadaverine (1,5-diaminopentane), and/or histamine (5-imidazole-ethylamine), the polymer typical undergoes a detectable color change from yellow to blue/violet. The color change may be in the UV, visible or near-infrared region of the spectrum, or some combination thereof, and will occur to the extent dependent on the concentration of biogenic amine to which the polymer is exposed. For food spoilage applications, significant color change will take place when the polymer is exposed to approximately 20 ppm or more of the biogenic amine. This polymer can be employed by itself or as a sensor to monitor the presence of biogenic amine in food products, particularly meats and fish. For example, the polymer can be easily incorporated into common food containers to provide and easily detectable indication of probable spoilage of food contents within the container, or employed in fiber optic detection devices.
*US and international patents pending. JHU/APL is seeking an exlusive license partner for this technology.
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