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SYNOPSISThermal unfolding curves have been measured for a series of short alanine-based peptides that contain repeating sequences and varying chain lengths. Standard helix-coil theory successfully fits the observed transition curves, even for these short peptides. The results provide values for u, the helix nucleation constant, AH", the enthalpy change on helix formation, and for s( O"C), the average helix propagation parameter at 0°C. The enthalpy change agrees with the value determined calorimetrically. The success of helix-coil theory in describing the unfolding transitions of short peptides in water indicates that helical propensities, or s values, can be determined from substitution experiments in short alaninebased peptides.

The antimicrobial properties of 21 plant essential oils and two essences were investigated against five important food-borne pathogens, Campylobacter jejuni, Salmonella enteritidis, Escherichia coli, Staphylococcus aureus and Listeria monocytogenes. The oils of bay, cinnamon, clove and thyme were the most inhibitory, each having a bacteriostatic concentration of 0.075% or less against all five pathogens. In general, Gram-positive bacteria were more sensitive to inhibition by plant essential oils than the Gram-negative bacteria. Campylobacter jejuni was the most resistant of the bacteria investigated to plant essential oils, with only the oils of bay and thyme having a bacteriocidal concentration of less than 1%. At 35 degrees C, L. monocytogenes was extremely sensitive to the oil of nutmeg. A concentration of less than 0.01% was bacteriostatic and 0.05% was bacteriocidal, but when the temperature was reduced to 4 degrees, the bacteriostatic concentration was increased to 0.5% and the bacteriocidal concentration to greater than 1%.