[Thermal inactivation and storage behavior of technologically important enzymes. I. Horseradish and spinach peroxidase].

Summary

# Editorial Summary Park and Fricker (1977) investigated how two peroxidase enzymes—from horseradish and spinach—respond to heat treatment and storage, since understanding enzyme stability is crucial for feed processing and preservation in equine nutrition. Using defined chemical systems alongside spinach tissue, they measured thermal inactivation at various temperatures and pH levels, deriving z-values (temperature sensitivity coefficients) of 25.5°C for horseradish peroxidase, 13°C for isolated spinach peroxidase, and 18°C for peroxidase within spinach extract. Both enzymes showed greatest heat resistance at neutral pH (5.0–6.0) but became highly susceptible at pH 4.0, with horseradish peroxidase demonstrating notably greater thermal stability overall. Critically, the researchers observed that isolated enzyme behaved differently from enzyme in its natural matrix—a finding that questions whether laboratory heat-inactivation models reliably predict real-world feed behaviour—and detected enzyme regeneration during storage that varied with pH conditions. For equine professionals involved in feed production, forage conservation or supplementation with botanical ingredients, this suggests that standard heat-treatment protocols may not account for enzyme reactivation post-processing, and that pH management during storage could meaningfully influence nutrient bioavailability and feed stability.

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Key Findings

• •Horseradish peroxidase showed a z-value of 25.5°C while spinach peroxidase isolated showed 13°C, indicating different thermal sensitivities between enzyme sources
• •Both enzymes demonstrated maximum heat resistance at pH 5.0-6.0 (spinach) and pH 6.0 (horseradish), with high susceptibility at pH 4.0
• •Peroxidase activity regenerated during storage after heating, with regeneration extent dependent on pH conditions
• •Isolated spinach peroxidase behaved differently under heating compared to enzyme in natural spinach extract, suggesting model systems may not accurately predict food enzyme behavior