Physiology and characterization of a fungal milk-clotting enzyme from Aspergillus flavus

Area of Science:

• Microbiology
• Enzymology
• Food Science

Background:

• Rennin, crucial for cheesemaking, is traditionally sourced from animal stomachs.
• Exploring microbial sources for rennin-like enzymes offers potential alternatives.
• Aspergillus flavus is known to produce various extracellular enzymes.

Purpose of the Study:

• To investigate the production and properties of a rennin-like enzyme from Aspergillus flavus.
• To evaluate the enzyme's milk-clotting activity and stability under different conditions.

Main Methods:

• Cultivating Aspergillus flavus aerobically in whey media.
• Assessing enzyme activity at different growth stages and temperatures.
• Testing enzyme stability with heat, skim milk, calcium chloride, and pH variations.

Main Results:

• An active extracellular rennin-like enzyme was produced by Aspergillus flavus in whey.
• Optimal enzyme activity was observed after 3-4 days of growth at 25°C.
• Enzyme activity was heat-labile above 50°C but stabilized by skim milk up to 70°C.
• Calcium chloride (up to 1%) enhanced milk-clotting activity.
• Clotting time correlated inversely with protein concentration (0.2-0.6 mg/ml).
• The enzyme showed good stability at 37°C and pH 6.

Conclusions:

• Aspergillus flavus produces a promising rennin-like enzyme with potential applications in dairy processing.
• The enzyme's activity and stability can be modulated by environmental factors and additives.
• Further research could optimize production and explore its use as a rennin substitute.