Evaluation of Raw Milk Quality Tests

Area of Science:

• Dairy Science
• Food Microbiology

Background:

• Raw milk quality is crucial for consumer safety and product shelf-life.
• Psychrotrophic bacteria can negatively impact milk flavor and processing.
• Established standards for milk acceptance are essential for the dairy industry.

Purpose of the Study:

• To evaluate raw milk quality tests.
• To determine standards for milk acceptance.
• To investigate the prevalence and impact of proteolytic psychrotrophs in raw milk.

Main Methods:

• Analysis of 315 individual producer milk samples from four Georgia dairy companies.
• Quantification of proteolytic psychrotrophs, with identification of dominant genera.
• Measurement of proteolysis using Hull values.
• Sensory evaluation for "bitter" flavor incidence.

Main Results:

• 72% of samples (226/315) harbored proteolytic psychrotrophs, predominantly Pseudomonas.
• One dairy exhibited a higher prevalence of thermoduric psychrotrophs.
• A direct correlation was found between Hull values (proteolysis) and "bitter" flavor.
• Mean Hull value for "bitter" samples was 46 μg/ml, significantly higher than non-bitter samples.

Conclusions:

• Proteolytic psychrotrophs, particularly Pseudomonas, are common in raw milk.
• Proteolysis, indicated by Hull value, is a reliable indicator of "bitter" flavor development.
• Further research into milk quality standards and microbial control is warranted.