Involvement of Heterofermentative Lactobacilli in Development of Open Texture in Cheeses

Area of Science:

• Food Microbiology
• Dairy Science
• Cheese Quality

Background:

• Gas formation and fissure defects in cheese can negatively impact consumer acceptance.
• Understanding the microbial causes of these defects is crucial for improving cheese production.

Purpose of the Study:

• To microbiologically investigate the causes of gas formation and fissure defects in Canadian Cheddar and Oka cheeses.
• To identify specific microbial groups associated with these cheese quality issues.

Main Methods:

• Microbiological examination of defective and high-quality Canadian Cheddar and Oka cheese samples.
• Enumeration of various microbial groups including lactobacilli, lactic streptococci, coliforms, staphylococci, yeasts, molds, and Clostridia.
• Comparison of different culture media (APT, MRS, MRS pH 5.5, Rogosa agar) for lactobacilli viability assessment.

Main Results:

• Defective cheeses showed significantly higher numbers of lactobacilli, particularly heterofermentative types, and citrate-utilizing organisms compared to high-quality cheeses.
• APT and MRS media yielded higher viable lactobacilli counts than MRS adjusted to pH 5.5 or Rogosa agar, especially for younger cheese samples.
• No significant difference in lactic streptococci numbers was observed between good and rejected cheeses. Coliforms, staphylococci, yeasts, molds, and Clostridia were not correlated with late-stage gas formation.

Conclusions:

• Heterofermentative lactobacilli and citrate-utilizing microorganisms are key contributors to gas formation and fissure defects in Canadian Cheddar and Oka cheeses.
• Culture medium choice significantly impacts the accurate enumeration of lactobacilli in cheese.
• Certain microbial groups commonly found in cheese do not appear to be primary drivers of late-maturation gas defects.