Skim Milk as a Multifunctional Cryoprotectant for Fish Probiotic Enterococcus spp.: Impact on Viability During...

Area of Science:

• Microbiology
• Aquaculture
• Food Science

Background:

• Probiotics enhance host health and are crucial in aquaculture.
• Arapaima (Arapaima gigas) probiotics require effective preservation methods for stability.
• Lyophilization is a common method for preserving probiotic cultures.

Purpose of the Study:

• To evaluate cryoprotectants for arapaima probiotic bacteria (Enterococcus faecium CRBP46 and Enterococcus gallinarum CRBP19).
• To assess bacterial viability after lyophilization, storage, and simulated gastrointestinal fluid (SGF) exposure.
• To determine the impact of cryoprotectants on cell surface hydrophobicity and matrix ultrastructure.

Main Methods:

• Tested cryoprotectants: maltodextrin, skim milk, trehalose, sucrose, fructose, dextrose.
• Lyophilized Enterococcus spp. with cryoprotectants.
• Stored samples at -25 °C, 4 °C, and 25 °C for 120 days.
• Exposed bacteria to simulated gastrointestinal fluids (SGF).
• Evaluated cell viability, surface hydrophobicity, and ultrastructure via scanning electron microscopy.

Main Results:

• Skim milk, trehalose, and dextrose (for E. gallinarum) provided excellent protection during lyophilization (≥99.50% survival).
• All cryoprotectants maintained stability at freezing and refrigeration temperatures.
• Skim milk was superior for room temperature storage (120 days) and SGF stability (≥97% survival).
• Skim milk enhanced bacterial hydrophobicity and cell adhesion.
• Microscopy revealed cells embedded in a low-porosity skim milk matrix.

Conclusions:

• Skim milk is the most effective cryoprotectant for arapaima Enterococcus spp. under tested conditions.
• Skim milk ensures probiotic stability and viability exceeding formulation requirements.
• Findings support the development of stable, dry autochthonous probiotics for sustainable arapaima aquaculture.