61C-20 |
Altering antimicrobial efficiency of lysozyme against Listeria monocytogenes using high-intensity ultrasound |
J. BOLAND1, J. Weiss, C. Beckett, and P. M. Davidson. (1) Colloidal and Interfacial Food Science Laboratory, University of Tennessee, 2605 River Drive, Room 102, Knoxville, TN 37996 The antimicrobial activity of lysozyme may be influenced by its physicochemical properties (i.e., molecular structure, interfacial activity). Manipulation of these physical properties through application of novel processing techniques, such as high-intensity ultrasound, could yield antimicrobials with improved activity. The development of enhanced antimicrobials would enable food manufacturers to develop new products that are stable at room temperature and have a prolonged shelf life. The objective of this study was to investigate the influence of high-intensity ultrasound and heat on the inhibitory efficacy of lysozyme against Listeria monocytogenes. Listeria monocytogenes Scott A, 101, 310, 108, and V7 were grown in tryptose phosphate broth (TPB). Native, sonicated (intensity: 0.1 – 1 W/cm2, time: 10-300 s) and heat-treated (80ºC/20 min.) lysozyme were tested in a microbroth dilution assay in TPB at pH 6 incubated at 32ºC for 24 and 48 hours. Minimum inhibitory concentration (MIC) was defined as the lowest concentration inhibiting visual growth. The degree of protein denaturation was evaluated using a differential scanning calorimeter (DSC). The MICs of lysozyme varied slightly with strain. Native lysozyme MIC was 300 µg/ml to ≈350µg/ml (strain V7 most sensitive). After heat treatment, all antimicrobial activity was lost. Sonication of lysozyme at 0.2 W/cm2 for 15s reduced the MIC to 200 ppm for strains Scott A and 108, while the MIC increased for all other strains. Long sonication times (>15 min.) and high power levels (> 10 W/cm2) reduced activity similarly to heat-treated lysozyme. DSC measurements indicated that results could be explained in terms of the partial (at low ultrasonic intensities/short times) or complete denaturation (at high ultrasonic intensities/long times) of the protein molecule. The results suggest that partial denaturation of lysozyme may be used to enhance activity against Listeria monocytogenes strains. The results also suggested that ultrasonicated lysozyme retained some activity compared to heat treatred lysozyme.
Session 61C, Food Microbiology: General I
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