Proteolytic System of

Area of Science:

• Food Microbiology
• Biochemistry
• Dairy Science

Background:

• Lactic acid bacteria (LAB) are crucial for fermented dairy products, producing flavor and aroma metabolites.
• Microbial proteases in LAB hydrolyze proteins into peptides, essential for bacterial growth and releasing bioactive compounds.
• Different LAB genera possess distinct proteolytic systems tailored to their nutritional needs.

Purpose of the Study:

• To elucidate the differences in proteolytic systems between Streptococcus thermophilus and other common LAB genera (Lactococcus, Lactobacillus).
• To understand the specific mechanisms contributing to flavor and bioactive peptide generation in fermented dairy.

Main Methods:

• Review of genetic studies, in vitro assays, and in vivo tests.
• Comparative analysis of the three key components of the S. thermophilus proteolytic system.
• Examination of peptide transport systems (Dpp, Ami, Opp) and intracellular peptidases.

Main Results:

• S. thermophilus utilizes a cell-wall-linked serine proteinase activated under specific nutrient conditions.
• Its Ami system transports longer peptides (up to 23 amino acids) compared to the Opp system in Lactococcus/Lactobacillus (less than 13 amino acids).
• S. thermophilus possesses unique intracellular peptidases that release aromatic amino acids or related peptides.

Conclusions:

• The distinct proteolytic system of S. thermophilus contributes significantly to the complex flavor profiles and bioactive peptide content of fermented dairy products.
• Understanding these differences is vital for optimizing starter cultures and enhancing the quality of fermented foods.