Challenge testing of the lactoperoxidase system in pasteurized milk

Area of Science:

• Food microbiology
• Dairy science
• Enzyme technology

Background:

• The lactoperoxidase (LP) system is a natural defense mechanism in milk.
• Its role in inhibiting microbial growth during pasteurization requires further clarification.
• Pasteurization temperatures can impact enzyme activity and microbial survival.

Purpose of the Study:

• To investigate the efficacy of the LP system in preventing microbial spoilage in pasteurized milk.
• To assess the influence of different pasteurization temperatures on LP activity and milk quality.

Main Methods:

• Four key spoilage microorganisms were inoculated into LP-enriched ultra-heat treated (UHT) milk.
• Milk samples were subjected to pasteurization at 72°C/15s and 80°C/15s.
• Keeping quality (KQ) was assessed at optimal growth temperatures for each bacterium.

Main Results:

• An active LP system significantly improved the KQ of milk pasteurized at 72°C against Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus thermophilus.
• The LP system showed minimal effect at 80°C, likely due to enzyme inactivation.
• Bacillus cereus spore resistance to inactivation was unaffected by the LP system or pasteurization temperature.

Conclusions:

• The LP system, not heat-shocking of spores, is responsible for the enhanced keeping quality of milk pasteurized at 72°C compared to 80°C.
• Careful selection of pasteurization temperatures is crucial in commercial dairy practices.
• Increasing pasteurization temperature should not be used to mask raw milk quality issues.