Recent outbreaks of food borne illnesses continue to support the need for rapid and sensitive methods for detection of foodborne pathogens. A method for detecting Listeria monocytogenes in food samples was developed using an automated fiber-optic-based immunosensor, RAPTOR ™. Detection of L. monocytogenes in phosphate buffered saline (PBS) was performed to evaluate both static and flow through antibody immobilization methods for capture antibodies in a sandwich assay. Subsequent detection in frankfurter samples was conducted using a flow through immobilization system. A two stage blocking using biotinylated bovine serum albumin (b-BSA) and BSA was effectively employed to reduce the non-specific binding. The sandwich assay using static or flow through mode of antibody immobilization could detect 1×10 3 cfu/ml in PBS. However, the effective disassociation constant K d and the binding valences for static modes of antibody immobilization in spiked PBS samples was 4×10 5 cfu/ml and 4.9 as compared to 7×10 4 cfu/ml and 3.9 for flow through method of antibody immobilization. Thus the sensitive flow-through immobilization method was used to test food samples, which could detect 5×10 5 cfu/ml of L. monocytogenes in frankfurter sample. The responses at the lowest detectable cell numbers in the frankfurter samples was 92.5 ± 14.6 pA for L. monocytogenes to comparative responses of 27.9 ± 12.2 and 31 ± 14.04 pA obtained from Enterococcus Sensors 2006, 6 809 faecalis and Lactobacillus rhamnosus (control species), respectively. The effective K d and binding valency from spiked frankfurter samples was 4.8×10 5 cfu/ml and 3.1, thus showing highly sensitive detection can be achieved using the RAPTOR ™ biosensor even in the presence of other bacterial species in the matrix.
ABSTRACT:The term bio-active packaging refers to a packaging material that has been modified by the attachment or immobilization of bioactive components on the food contact surface. This article describes a novel, economical, and feasible technique for embedding bioactive components in energy curable food contact resins. While the technique is versatile and potentially applicable to any antimicrobial or bioactive compound; the proof of concept discussed in this article has focused on enzyme immobilization. Glucose oxidase (GOx) and catalase were used as representative enzymes. These oxidoreductases are very sensitive to inactivation by extrinsic factors and therefore present a challenging model for immobilization. Embedding of activity occurred via UV polymerization of commercial polymer coatings. The efficiency of immobilization and the performance of bioactive packaging were tested in both food simulants and actual food products. In both cases immobilization resulted in food contact surfaces with high retained enzyme activity as demonstrated by oxygen removal.
Bioactive packaging is an important area of active packaging in which an active component is incorporated into the food contact surface of the package to interact with the food components without itself migrating into the food. Embedding bioactivity in a UV polymerizable resin is a novel and versatile technique for incorporating bioactive components into food packaging. In a previous article, glucose oxidase was immobilized in a packaging material using a UV curable resin. The relevance of this model system for deoxygenation of fruit juices was discussed. Though the technique efficiently immobilized enzymes in packaging material, during polymerization and immobilization the catalytic ability of the enzyme was not specifically explored. This article compares and contrasts the catalytic ability in terms of the kinetic profile of free and immobilized enzyme for the same model system: deoxygenation of juices. Kinetic behavior of immobilized and free glucose oxidase enzyme was evaluated at both shelf stable (room temperature) and refrigerated storage conditions to simulate the actual package life. It was observed that both the free enzyme and the immobilized enzymes follow the Michaelis-Menten kinetics model. There was no significant difference between the catalytic ability (k(cat)/K(m)) of free and immobilized enzymes at treatment temperatures (30, 25, and 10 degrees C); however, at refrigeration temperature (5 degrees C), the values for free enzyme were significantly higher than the immobilized enzyme.
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