The bactericidal effect of isoascorbic acid combined with mild heat

Area of Science:

• Food Microbiology
• Food Safety
• Antimicrobial Mechanisms

Background:

• Thermal processing is crucial for eliminating microbial contamination in food.
• Understanding factors that enhance microbial inactivation is vital for food safety.
• Ascorbate derivatives are common food additives with potential pro-oxidant effects.

Purpose of the Study:

• To investigate the effect of sodium isoascorbate on the thermal inactivation of various foodborne microorganisms.
• To elucidate the mechanism underlying the enhanced lethal effect of sodium isoascorbate during heating.

Main Methods:

• Heating of specific bacterial and yeast strains (Salmonella thompson, E. coli, S. aureus, C. perfringens, C. zeylanoides, E. faecium, E. faecalis) in phosphate buffer with and without sodium isoascorbate.
• Testing the influence of anaerobic conditions, catalase, hydroxyl radical scavengers (mannitol, formate, histidine), and superoxide dismutase on inactivation.
• Evaluating the role of dehydroascorbic acid and its interaction with catalase.

Main Results:

• Sodium isoascorbate (1 mmol/l) accelerated the thermal inactivation of tested microorganisms in phosphate buffer but not in complex food matrices.
• The lethal effect of isoascorbate was negated by anaerobic conditions or the addition of catalase, suggesting an oxidative mechanism.
• Histidine offered protection, potentially by inhibiting isoascorbate autoxidation, while other radical scavengers were ineffective; dehydroascorbic acid also enhanced heat killing.

Conclusions:

• The enhanced thermal inactivation by sodium isoascorbate and dehydroascorbic acid appears to depend on oxidative processes.
• The mechanism may involve site-specific redox reactions, possibly through amino-carbonyl intermediates.
• These findings have implications for optimizing thermal food processing and understanding antimicrobial actions of food additives.