Iron binding characteristics of phenolic compounds: some tentative structure-activity relations

S Khokhar, Richard Owusu-Apenten

Research output: Contribution to journalArticle

220 Citations (Scopus)

Abstract

Two mechanisms are commonly proposed to explain the antioxidant role of phenolic compounds; these are metal chelation and/or free radical scavenging. However, the structural requirements for each may not be the same. This paper describes the determination of iron-binding efficiencies (in vitro) for a series of pure phenolics of known structure [gallic acid, tannic acid, catechin, epicatechin (EC), epicatechingallate (ECG), epigallocatechin (EGC), epigallocatechingallate (EGCG) and quercetin] and of tea beverages of known flavonoid composition. Iron-binding efficiency was measured as catechin equivalents or tannic acid equivalents using the two wavelength assay. High catechin equivalents require the presence of a 3',4' dihydroxy (catechol) group on flavanoid ring B. In contrast, the presence of a 3',4',5-trihydroxy (galloyl) group of ring B (epigallocatechin) or ring C (epicatechin gallate) was associated with reduced Fe-binding. The extent of Fe-binding was also found to be lower for quercetin than catechin, which is probably due to the presence of conjugation extending from the C4-keto group, via C2-3 to the 3'-OH group (rings B and Q. For the polyphenols examined, catechin equivalents were inversely correlated with tannic acid equivalents and with antioxidant activity of flavonoids, as measured by the TEAC assay. Requirements for efficient iron-binding are discussed.
LanguageEnglish
Pages133-140
JournalFood Chemistry
Volume81
Issue number1
DOIs
Publication statusPublished - May 2003

Fingerprint

Catechin
Iron
Tannins
Quercetin
Flavonoids
Assays
Antioxidants
Gallic Acid
Beverages
Scavenging
Polyphenols
Chelation
Free Radicals
Metals
Wavelength
Chemical analysis

Keywords

  • polyphenols
  • flavonoids
  • catechin
  • tea
  • iron-binding
  • metal-chelation
  • antioxidant activity
  • ANTIOXIDANT ACTIVITIES
  • FLAVONOIDS
  • ABSORPTION
  • TEA
  • BIOAVAILABILITY
  • POLYPHENOLS

Cite this

Khokhar, S ; Owusu-Apenten, Richard. / Iron binding characteristics of phenolic compounds: some tentative structure-activity relations. 2003 ; Vol. 81, No. 1. pp. 133-140.
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note = "Reference text: 1. AFANASEV IB CHELATING AND FREE-RADICAL SCAVENGING MECHANISMS OF INHIBITORY-ACTION OF RUTIN AND QUERCETIN IN LIPID-PEROXIDATION BIOCHEMICAL PHARMACOLOGY 38 : 1763 1989 2. ARORA A Structure-activity relationships for antioxidant activities of a series of flavonoids in a liposomal system FREE RADICAL BIOLOGY AND MEDICINE 24 : 1355 1998 3. BABA S Bioavailability of (-)-epicatechin upon intake of chocolate and cocoa in human volunteers FREE RADICAL RESEARCH 33 : 635 2000 4. BORS W FLAVONOIDS AS ANTIOXIDANTS - DETERMINATION OF RADICAL-SCAVENGING EFFICIENCIES METHODS IN ENZYMOLOGY 186 : 343 1990 5. BRUNE M IRON-ABSORPTION AND PHENOLIC-COMPOUNDS - IMPORTANCE OF DIFFERENT PHENOLIC STRUCTURES EUROPEAN JOURNAL OF CLINICAL NUTRITION 43 : 547 1989 6. BRUNE M DETERMINATION OF IRON-BINDING PHENOLIC GROUPS IN FOODS JOURNAL OF FOOD SCIENCE 56 : 128 1991 7. CHENG IF BIOMATERIALS 13 : 7 2000 8. DISLER PB GUT 32 : 2484 1975 9. DUTHIE GG Plant polyphenols in cancer and heart disease: implications as nutritional antioxidants NUTRITION RESEARCH REVIEWS 13 : 79 2000 10. GRINBERG LN Protective effects of tea polyphenols against oxidative damage to red blood cells BIOCHEMICAL PHARMACOLOGY 54 : 973 1997 11. HALIWELL B METHOD ENZYMOL 186 : 1 1990 12. HALLBERG L Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron AMERICAN JOURNAL OF CLINICAL NUTRITION 71 : 1147 2000 13. HARPER KA J FOOD TECHNOL 4 : 255 1969 14. HUDSON BJF POLYHYDROXY FLAVONOID ANTI-OXIDANT FOR EDIBLE OILS - STRUCTURAL CRITERIA FOR ACTIVITY FOOD CHEMISTRY 10 : 47 1983 15. KHOKHAR S A RP-HPLC method for the determination of tea catechins CANCER LETTERS 114 : 171 1997 16. KHOKHAR S Total phenol, catechin, and caffeine contents of teas commonly consumed in the United Kingdom JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 50 : 565 2002 17. KUHNLE G Epicatechin and catechin are O-methylated and glucuronidated in the small intestine BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS 277 : 507 2000 18. LAUGHTON MJ BIOCHEM PHARMACOL 36 : 717 1987 19. LETAN A J FOOD SCI 31 : 395 1996 20. LOPES GKB Polyphenol tannic acid inhibits hydroxyl radical formation from Fenton reaction by complexing ferrous ions BIOCHIMICA ET BIOPHYSICA ACTA-GENERAL SUBJECTS 1472 : 142 1999 21. MORETTI G Tools improve runtimes, DFT capabilities EDN 45 : 16 2000 22. PRIOR RL Antioxidant phytochemicals in fruits and vegetables: Diet and health implications HORTSCIENCE 35 : 588 2000 23. RICEEVANS CA THE RELATIVE ANTIOXIDANT ACTIVITIES OF PLANT-DERIVED POLYPHENOLIC FLAVONOIDS FREE RADICAL RESEARCH 22 : 375 1995 24. SPENCER JPE BIOCHEM J 352 : 493 1999 25. ZIJP IM Effect of tea and other dietary factors on iron absorption CRITICAL REVIEWS IN FOOD SCIENCE AND NUTRITION 40 : 371 2000",
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Iron binding characteristics of phenolic compounds: some tentative structure-activity relations. / Khokhar, S; Owusu-Apenten, Richard.

Vol. 81, No. 1, 05.2003, p. 133-140.

Research output: Contribution to journalArticle

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T1 - Iron binding characteristics of phenolic compounds: some tentative structure-activity relations

AU - Khokhar, S

AU - Owusu-Apenten, Richard

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Y1 - 2003/5

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AB - Two mechanisms are commonly proposed to explain the antioxidant role of phenolic compounds; these are metal chelation and/or free radical scavenging. However, the structural requirements for each may not be the same. This paper describes the determination of iron-binding efficiencies (in vitro) for a series of pure phenolics of known structure [gallic acid, tannic acid, catechin, epicatechin (EC), epicatechingallate (ECG), epigallocatechin (EGC), epigallocatechingallate (EGCG) and quercetin] and of tea beverages of known flavonoid composition. Iron-binding efficiency was measured as catechin equivalents or tannic acid equivalents using the two wavelength assay. High catechin equivalents require the presence of a 3',4' dihydroxy (catechol) group on flavanoid ring B. In contrast, the presence of a 3',4',5-trihydroxy (galloyl) group of ring B (epigallocatechin) or ring C (epicatechin gallate) was associated with reduced Fe-binding. The extent of Fe-binding was also found to be lower for quercetin than catechin, which is probably due to the presence of conjugation extending from the C4-keto group, via C2-3 to the 3'-OH group (rings B and Q. For the polyphenols examined, catechin equivalents were inversely correlated with tannic acid equivalents and with antioxidant activity of flavonoids, as measured by the TEAC assay. Requirements for efficient iron-binding are discussed.

KW - polyphenols

KW - flavonoids

KW - catechin

KW - tea

KW - iron-binding

KW - metal-chelation

KW - antioxidant activity

KW - ANTIOXIDANT ACTIVITIES

KW - FLAVONOIDS

KW - ABSORPTION

KW - TEA

KW - BIOAVAILABILITY

KW - POLYPHENOLS

U2 - 10.1016/S0308-8146(02)00394-1

DO - 10.1016/S0308-8146(02)00394-1

M3 - Article

VL - 81

SP - 133

EP - 140

IS - 1

ER -