Psychrotrophic Bacteria Reduce Cheese Yield ¹.

Area of Science:

• Food Microbiology
• Dairy Science
• Biochemistry

Background:

• Psychrotrophic bacteria, including Bacillus and Pseudomonas species, are common contaminants in raw milk.
• These bacteria can produce enzymes like proteases and lipases, which degrade milk components during refrigerated storage.
• Such degradation can negatively impact milk quality and the yield of dairy products.

Purpose of the Study:

• To investigate the impact of psychrotrophic bacterial inoculation on direct-acid cheese yield.
• To determine the extent of lipid and protein degradation contributing to yield loss.
• To identify reliable indicators for monitoring yield reduction.

Main Methods:

• Grade A milk was inoculated with psychrotrophic Bacillus and Pseudomonas strains at varying levels.
• Direct-acid cheese was manufactured from the inoculated milk.
• Analysis included milkfat tests, acid degree values, non-protein nitrogen, whey nitrogen, and dry matter loss assessments.

Main Results:

• Cheese yield decreased significantly with increasing psychrotrophic inoculation levels.
• Lipid and protein degradation accounted for approximately 45% and 55% of dry matter loss, respectively.
• Increased acid degree values and fat disappearance in milk, along with total nitrogen in whey, were strong indicators of yield reduction.

Conclusions:

• Psychrotrophic bacterial activity significantly reduces direct-acid cheese yield through lipid and protein degradation.
• Accurate cheese yield assessments require analysis of both protein and lipid content on a dry matter basis.
• Acid degree values, fat disappearance, and whey nitrogen are key indicators for predicting and monitoring yield losses.