title: Challenge testing of the lactoperoxidase system in pasteurized milk.
abstract: OBJECTIVE
  To determine the role of lactoperoxidase (LP) in inhibiting the growth of micro-organisms in pasteurised milk.
  
  
  RESULTS
  Four micro-organisms of importance in the spoilage of pasteurized milk were challenged in lactoperoxidase (LP)-enriched ultra-heat treated (UHT) milk after subsequent pasteurization. Milk samples were stored at the optimum temperatures for growth of the individual bacteria. Pasteurization was carried out at 72 degrees C/15 s and 80 degrees C/15 s to determine the effect of the LP system on the micro-organisms. An active LP system was found to greatly increase the keeping quality (KQ) of milks inoculated with Pseudomonas aeruginosa, Staphylococcus aureus and Streptococcus thermophilus and pasteurized at 72 degrees C, but had little or no effect in milks heated at 80 degrees C, presumably due to virtual inactivation of LP at 80 degrees C. However, pasteurization temperature had no effect on the KQ of milks challenged with Bacillus cereus spores.
  
  
  CONCLUSIONS
  This study suggests that the LP system, rather than heat-shocking of spores, is responsible for the greater KQ of milk pasteurized at 72 degrees C/15 s compared with 80 degrees C/15 s.
  
  
  CONCLUSIONS
  The study emphasizes the care required in selecting pasteurization temperatures in commercial practice and to avoid the temptation to compensate for inferior quality of raw milk by increasing pasteurization temperature.
authors.affiliation: School of Food Biosciences, The University of Reading, UK.
authors.forename: N E
authors.initials: NE
authors.lastname: Marks
authors.forename: A S
authors.initials: AS
authors.lastname: Grandison
authors.forename: M J
authors.initials: MJ
authors.lastname: Lewis
mesh_terms: D000818:Animals; D001419:Bacteria / Q000254:growth & development* / Q000302:isolation & purification; D015169:Colony Count, Microbial; D005511:Food Handling / Q000379:methods; D006358:Hot Temperature; D007784:Lactoperoxidase / Q000378:metabolism*; D008892:Milk / Q000201:enzymology* / Q000382:microbiology*; D011786:Quality Control; D013171:Spores, Bacterial / Q000254:growth & development / Q000302:isolation & purification
chemical_list: D007784:Lactoperoxidase