Streptococcus thermophilus
Probiotics & Enzymes
Overview
- Streptococcus thermophilus is a Gram-positive, facultatively anaerobic, non-spore-forming cocci.
- It thrives at temperatures of 42–45 °C.
- It is widely recognized as a starter culture in dairy fermentation (yogurt, cheese).
- It produces lactic acid, contributes to texture, extends shelf-life, and delivers live probiotic cells.
Chemistry
- Microorganism: Streptococcus thermophilus is a living microorganism; therefore, it does not have a single molecular formula.
- Genome: Its genome is a circular chromosome of ~1.9 Mbp, encoding ~1,800 proteins.
- Cell Wall: The cell wall is composed of a thick peptidoglycan layer (N-acetylmuramic acid–N-acetylglucosamine polymer cross-linked by L-lysine–D-alanine bridges) with teichoic acids (ribitol-phosphate polymers) that confer the characteristic Gram-positive staining.
- Surface Proteins: Major surface proteins include the M protein-like adhesins (e.g., SrtA-anchored proteins) and exopolysaccharide (EPS) biosynthetic enzymes (e.g., glycosyltransferases).
- Metabolic Pathways: The bacterium’s metabolic pathways include glycolysis, the pentose-phosphate pathway, and the L-lactate dehydrogenase–mediated conversion of pyruvate to L-lactate (ΔG ≈ −25 kJ mol⁻¹).
- EPS Production: The EPS produced are high-molecular-weight polysaccharides (≈10⁶ Da) composed mainly of glucose, galactose, and N-acetylglucosamine.
Sources & Quality
- Natural Source: Streptococcus thermophilus is isolated from traditional dairy fermentations (e.g., yogurt, cheese) where it naturally dominates at thermophilic temperatures.
- Commercial Production: Commercial production utilizes controlled fermentation of sterile milk or whey media in bioreactors at 42–45 °C, yielding high-density cultures (≥10¹⁰ CFU mL⁻¹).
- Strain Selection: Strains are selected for robust β-galactosidase activity, acid tolerance, and stable exopolysaccharide production.
- Processing: After fermentation, cells are harvested, lyophilized, and encapsulated (e.g., double-layer microencapsulation) to protect viability.
- Quality Control: Quality control includes strain identification by 16S rRNA sequencing, absence of pathogenic genes (e.g., cagA, vir), and CFU verification per label claim.
- Manufacturing Standards: Good Manufacturing Practice (GMP) and third-party testing (e.g., USP, NSF) are essential to ensure purity, potency, and absence of contaminants (e.g., E. coli, Salmonella).
Where to Buy Streptococcus thermophilus
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