Effect of Alpha-Tocopherol and Some Flavonoid Compounds on Inactivation of Peroxidase (Purified and Unpurified) of Selected Vegetables
Hemeda, Hanaa Mohamed
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https://hdl.handle.net/2142/71748
Description
Title
Effect of Alpha-Tocopherol and Some Flavonoid Compounds on Inactivation of Peroxidase (Purified and Unpurified) of Selected Vegetables
Author(s)
Hemeda, Hanaa Mohamed
Issue Date
1988
Doctoral Committee Chair(s)
Klein, Barbara
Department of Study
Human Resources and Family Studies
Discipline
Human Resources and Family Studies
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Food Science and Technology
Abstract
The effect of natural antioxidants (alpha-tocopherol, quercetin, rutinic acid and chlorogenic acid) at four different concentrations (125, 250, 500 and 1000 mg%) on peroxidase activity of tomato, eggplant and carrot was determined. All antioxidants caused reduction in peroxidase activity of crude extracts of three vegetables. As the concentration of antioxidants increased, the percent peroxidase activity remaining decreased. Alpha-tocopherol was found to be a weak inhibitor compared to flavonoids. The greatest reduction in peroxidase activity of tomato, eggplant and carrot occurred with chlorogenic acid.
Thermal inactivation of peroxidase activity of tomato, carrot and eggplant at 75$\sp\circ$C for different periods of time (0.5, 1.0, 1.5 and 2.0 min) with and without antioxidants was investigated. Flavonoids were found to be more effective than alpha-tocopherol without heat treatment. The combination of heat treatment and antioxidants was most effective in reducing residual peroxidase activity. Regeneration of peroxidase after 3 hr at 28$\sp\circ$C was observed in crude extracts which were heat treated only. Antioxidants continued to inhibit peroxidase activity during frozen storage for 4 wk at -18$\sp\circ$C. Peroxidase activity of both tomato and eggplant dropped to zero in extracts that were treated with antioxidants for 1.5 and 2.0 min. Carrot peroxidase activity dropped to zero after 2.0 min heat treatment with antioxidants.
Crude extracts (tomato, eggplant and carrot) heated at 100$\sp\circ$C for different periods of time affected peroxidase activity of unheated purified horseradish peroxidase. Tomato extract (heated 2 min) reduced peroxidase activity of eggplant and carrot. Eggplant (heated 3 min) reduced peroxidase activity of tomato and carrot. Carrot extract (heated 10 min) reduced peroxidase activity of tomato and eggplant. The 3 min heated crude vegetable extracts reduced the activity of purified horseradish peroxidase.
Partially purified tomato and carrot peroxidase was obtained using ammonium sulfate fractionation (50-90%), gel filtration (sephadex G-200), and ion-exchange chromatography (QAE sephadex A-50). The inhibitory effect of antioxidants (alpha-tocopherol, quercetin, rutinic acid and chlorogenic acid), heat treatment and a combination of heat treatment and antioxidant on acitivity of purified tomato and carrot peroxidase were compared, and reactivation of peroxidase activity after 3 hr at 28$\sp\circ$C was determined. Flavonoid compounds with and without heat treatment were found to be superior to alpha-tocopherol in reducing peroxidase activity. Regeneration of peroxidase activity was minimal in samples treated with antioxidant.
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