15A-17 |
A sensitive fluorescence assay method for measurement of nisin released from nisin-embedded packaging materials |
Y. ZHANG, M. L. Tchikindas, and K. Yam. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901 There is an increasing demand for reliable and sensitive method to detect and quantify the bio-preservative nisin. Tramer’s Well Diffusion Assay is commonly used, however, it has low sensitivity and low specificity. Recently, it has been reported that the b-glucuronidase assay (GUS assay) can be used to determine low concentrations of nisin. Our objective was to use the GUS assay to quantify release of nisin from nisin-embedded packaging materials. Lactococcus lactis NZ9800 cells were transformed with a plasmid carrying b-glucuronidase gene under the control of nisin-inducible promoter. In the presence of nisin, b-glucuronidase is produced and reacts with a substrate, and the fluorescence is quantified by spectrofluorimeter (LS 50B, Perkin Elmer). The nisin concentration is then correlated to the fluorescence value, based on a standard curve. Our results showed that fluorescence values were concentration dependent and the sensitivity of detection was very high (ng/ml). Both the 96-well-plate and the single cuvette methods were equally sensitive, but the 96-well-plate method is more convenient. Samples which are frozen immediately upon nisin induction had the same sensitivity as the fresh samples. These data suggest that the GUS assay can be used in the food industry to detect the concentration of nisin released from nisin-embedded packaging materials or present in foods. The GUS assay is reliable and easy to use. With its high sensitivity, it will help us to gain a better understanding of the release phenomena of nisin from the nisin-embedded packaging materials, and diffusion kinetics of nisin within the products.
Session 15A, Biotechnology
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