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Ascorbate radicals in fresh cow's milk

M Nakamura1

  • 1Research Institute for Electronic Science, Hokkaido University, Sapporo.

Journal of Biochemistry
|September 1, 1994
PubMed
Summary
This summary is machine-generated.

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Fresh cow's milk contains ascorbate free radicals, detected by ESR. Lactoperoxidase activity in milk contributes to the formation of these radicals when exposed to hydrogen peroxide or xanthine.

Area of Science:

  • Biochemistry
  • Food Science
  • Analytical Chemistry

Background:

  • Ascorbate free radical (AFR) presence and stability in milk are not fully understood.
  • Cow's milk contains enzymes like xanthine oxidase and lactoperoxidase that can generate reactive oxygen species.
  • The role of these enzymes in AFR formation in milk requires further investigation.

Purpose of the Study:

  • To detect and characterize the ascorbate free radical in fresh cow's milk using Electron Spin Resonance (ESR).
  • To investigate the influence of storage temperature and the addition of hydrogen peroxide (H2O2) or xanthine on AFR concentration.
  • To determine the enzymatic basis for H2O2- and xanthine-induced AFR formation in cow's milk.

Main Methods:

  • Electron Spin Resonance (ESR) spectroscopy was used to detect and quantify the ascorbate free radical.

Related Experiment Videos

  • Cow's milk samples were stored at different temperatures (5°C and 25°C) and analyzed.
  • Enzymatic activities, including xanthine-oxygen reductase and peroxidase, were measured to quantify enzyme concentrations.

    • Main Results:

    • A weak ESR signal attributed to the ascorbate free radical was observed in fresh cow's milk.
    • The AFR signal persisted after 24h storage at 5°C but disappeared at 25°C.
    • Addition of H2O2 or xanthine markedly increased steady-state AFR concentration, an effect abolished by azide, indicating enzymatic involvement.

    Conclusions:

    • Cow's milk contains measurable levels of ascorbate free radical.
    • Storage temperature significantly affects the stability of the ascorbate free radical in milk.
    • The ascorbate peroxidase activity of lactoperoxidase in cow's milk is responsible for H2O2- and xanthine-induced AFR formation.