Listeria monocytogenes inhibition by whey protein films and coatings incorporating lysozyme.
The effects of whey protein isolate (WPI) films and coatings incorporating lysozyme (LZ) on the inhibition of Listeria monocytogenes both in and on microbial media, as well as on cold-smoked salmon, were studied. The antimicrobial effects of LZ were examined using various growth media by turbidity and plate counting tests. Disc-covering and disc-surface-spreading tests were also used to evaluate the effects of WPI films incorporating LZ. Smoked salmon was used as a model food to test the antimicrobial effects of WPI coatings incorporating LZ, both initially and during storage at 4 and 10 degrees C for 35 days. Tensile properties (elastic modulus, tensile strength, and percentage of elongation), oxygen permeability, and color (Hunter L, a, and b) of WPI films with and without LZ were also compared. LZ inhibited L. monocytogenes in broth and on agar media. The number of cells surviving after LZ treatments depended on the type of media. WPI films incorporating 204 mg of LZ per g of film (dry basis) inhibited the growth of a preparation of 4.4 log CFU/cm2 L. monocytogenes. WPI coatings prepared with 25 mg of LZ per g of coating solution initially inactivated more than 2.4, 4.5, and 3.0 log CFU/g of L. monocytogenes, total aerobes, and yeasts and molds in smoked salmon samples, respectively. The WPI coatings incorporating LZ efficiently retarded the growth of L. monocytogenes at both 4 and 10 degrees C. The anti-L. monocytogenes effect of LZ-WPI coating was more noticeable when the coating was applied before inoculation than when the coating was applied after inoculation. Significantly higher elastic modulus values and lower percentage of elongation and oxygen permeability values were measured with the WPI films incorporating LZ than with the plain WPI films.
Min
Seacheol
S
Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, California 95616, USA.
Harris
Linda J
LJ
Han
Jung H
JH
Krochta
John M
JM
D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology; D015169:Colony Count, Microbial; D005511:Food Handling / Q000379:methods; D005519:Food Preservation / Q000379:methods*; D005520:Food Preservatives / Q000494:pharmacology; D008089:Listeria monocytogenes / Q000187:drug effects / Q000254:growth & development*; D008894:Milk Proteins / Q000494:pharmacology*; D009113:Muramidase / Q000494:pharmacology*; D010100:Oxygen / Q000378:metabolism; D010858:Pigmentation; D012474:Salmon / Q000382:microbiology*; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors; D000067816:Whey Proteins
D000890:Anti-Infective Agents; D005520:Food Preservatives; D008894:Milk Proteins; D000067816:Whey Proteins; D009113:Muramidase; D010100:Oxygen