Nisin, an antimicrobial peptide used in food preservation was
evaluated for thermal stability. Nisin retained antimicrobial
activity after having been heated at 121��C for seven hours.
Anhydrous nisin and concentrated nisin solutions (5-10 mg/ml) were
still active after having been heated up to 190��C or 230��C. When
exposed to high temperatures of 200 or 250��C for up to one hour,
nisin lost all antimicrobial activity.
After 3.5 hours of heating at 121��C an inactive nisin
degradation product, designated nisin L, was isolated. In comparison
to native nisin, nisin L had reduced activity against Pediococcus
pentosaceus FBB-61 and no activity against Bacillus cereus T
vegetative cells or spores. Structural changes to nisin L were
studied by high performance liquid chromatography (HPLC), ion spray
mass spectroscopy (MS), ��H nuclear magnetic resonance
spectroscopy (NMR) and circular dichroism (CD) spectroscopy and
compared to original nisin.
There was no difference in molecular weight between nisin and
nisin L. Both MS spectra contained nisin, with average molecular
weight (MW) of 3354 daltons (D), and hydrated nisin with average
molecular weight of 3372 D. Nisin L had higher proportion of
hydrated molecules, and it had molecules with more then one water
addition. Proton NMR analysis of nisin L indicated that
dehydrobutyrine 2 and dehydroalanine 5 residues had been altered,
and that several new hydrogen resonances appeared. Water additions
in nisin L are likely to have occurred at dehydroresidues, making
them inactive. Nisin L was found to be more polar, as would be
expected for a more hydrated peptide. Analysis of CD spectra
indicated that nisin L had smaller content of a helix and therefore
lesser membrane spanning capability. Tandem mass spectroscopy of
original nisin revealed that it was hydrated at lysine 34 residue. / Graduation date: 1996
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34669 |
| Date | 12 January 1996 |
| Creators | Musafija-Jeknic, Tamara |
| Contributors | Daeschel, Mark A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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