EFFECTS OF PROCESSING ON THE CHEMISTRY AND ANTIOXIDANT CAPACITY OF ...

221 Pages·2009·1.44 MB·English

EFFECTS OF PROCESSING ON THE CHEMISTRY AND ANTIOXIDANT CAPACITY OF
ENDOGENOUS BIOACTIVE COMPOUNDS IN PEANUT KERNELS AND SKINS
by
BRIAN DAVID CRAFT
(Under the Direction of Ronald Bruce Pegg)
ABSTRACT
The overall aims of this work were to ascertain the primary phenolic constituents in
peanut kernels and skins, and determine if there antioxidant content and capacities are conserved
through industrial roasting processes. The first study conducted revealed that the predominant
phenolic compounds in peanut kernels are free/bound p-coumaric acids, which are released from
their ester or glycoside forms during thermal treatment. This observed increase in p-coumaric
acid levels was affected both by peanut type and processing method. A Spanish high-oleic
cultivar had the highest naturally occurring levels of free/bound p-coumaric acids and a high-
oleic Runner yielded an increase of ~785% in free p-coumaric acid from raw to oil-roasted
sample. The total phenolic contents and antioxidant capacities of processed peanut kernels from
the 2007 crop were found to increase in a stepwise fashion from raw < dry-roast < oil-roast for
nearly all phytochemical analyses performed. This suggests that although the chemistry of
phenolic compounds in peanuts is changing through roasting, their antioxidant potency is
preserved and sometimes increased. The second and third studies undertaken involved the
chromatographic characterization of low- (LMW) and high-molecular-weight (HMW) phenolic
fractions isolated from dry-blanched (DB) and dry-roasted (DR) peanut skins. Catechin,
epicatechin, and p-coumaric acid esters were identified in the LMW fraction of DB peanut skins;
whereas catechin, free p-coumaric and protocatechuic acids, and a protocatechuic acid ester were
found in DR skins. Total phenolics and antioxidant capacities were similar for DB and DR skins.
Some of the collected LMW fractions exhibited higher antioxidant capacities than their
corresponding crude extracts; suggesting that LMW phenolics contribute to peanut skin’s total
antioxidant capacity. Proanthocyanidin (PAC) analyses showed that DR peanut skin tannins have
a higher degree of polymerization than DB skins. A greater incidence of PAC polymerization
reactions may be a result of the higher temperatures involved in the dry-roasting process. All
three studies indicated that processing is altering the chemistry of the phenolics in peanuts and
peanut skins, but their antioxidant efficacy is retained for the consumer.

INDEX WORDS: Peanuts, Peanut Skins, Peanut Industry, Peanut Processing, Roasting,
Antioxidants, Phenolics, Proanthocyanidins
EFFECTS OF PROCESSING ON THE CHEMISTRY AND ANTIOXIDANT CAPACITY OF
ENDOGENOUS BIOACTIVE COMPOUNDS IN PEANUT KERNELS AND SKINS

by

BRIAN DAVID CRAFT
B.S., University of Florida, 2005

A Dissertation Submitted to the Graduate Faculty of the University of Georgia in Partial
Fulfillment of the Requirements for the Degree

DOCTORATE OF PHILOSOPHY

ATHENS, GEORGIA
2009
© 2009
Brian David Craft
All Rights Reserved
EFFECTS OF PROCESSING ON THE CHEMISTRY AND ANTIOXIDANT CAPACITY OF
ENDOGENOUS BIOACTIVE COMPOUNDS IN PEANUT KERNELS AND SKINS

by

BRIAN DAVID CRAFT

Major Professor: Ronald B. Pegg

Committee: Ronald R. Eitenmiller
Phillip Greenspan
William L. Kerr
Robert L. Shewfelt

Electronic Version Approved:

Maureen Grasso
Dean of the Graduate School
The University of Georgia
August 2009
DEDICATION
This work is dedicated to my loving parents, David and Janet Craft, to whom I owe my
undying gratitude. Also, to my beautiful puppy Kane (“Bubba”), who taught me patience and
selfless love in his lifetime.

iv
ACKNOWLEDGEMENTS
First off, I would like to thank my advisor Dr. Ronald B. Pegg for his constant guidance
and support in this endeavor. I would also like to thank my committee members Dr. Robert L.
Shewfelt, Dr. Ronald R. Eitenmiller, Dr. William L. Kerr, and Dr. Phillip Greenspan for tutoring
and looking after me during my term at the University of Georgia. I would like to acknowledge
Prof. Dr. Ryszard Amarowicz and his technician Agnieszka Kosińska of the Division of Food
Science, Institute of Animal Reproduction and Food Research of the Polish Academy of
Sciences, Olsztyn, Poland for their technical assistance. Lastly, I would like to thank my loving
family and friends for standing by me, through the good times and bad.

Sincerely,
Brian D. Craft

v
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS.............................................................................................................v
LIST OF TABLES.......................................................................................................................viii
LIST OF FIGURES.......................................................................................................................ix
CHAPTER
1 INTRODUCTION.........................................................................................................1
1.1 Peanuts and Human Health.............................................................................1
1.2 U.S. Peanut Production...................................................................................2
1.3 Significance of Peanut Skins..........................................................................2
1.4 Phenolic Antioxidants in Peanut Kernels.......................................................3
1.5 The Effects of Processing on Peanut Antioxidants.........................................3
1.6 Polyphenolic Antioxidants in Processed Peanut Skins...................................4
1.7 Peanut Sample Set...........................................................................................4
1.8 The Goals of the Work....................................................................................5
2 LITERATURE REVIEW............................................................................................13
2.1 Reactive Oxygen Species (ROS) and the Human Body...............................13
2.2 Oxidation, Antioxidation, and Reduction.....................................................15
2.3 Phenolic and Polyphenolic Antioxidants......................................................19
2.4 Free Radical Theory: Basis for Quantification of Antioxidant Capacity.....24
2.5 In Vitro Antioxidant-Screening Methods of Critical Importance.................38
vi
2.6 Phenolic Source Under Examination: The Peanut (Arachis hypogaea L.)...51
3 PHENOLIC PROFILES AND ANTIOXIDANT/RADICAL-SCAVENGING
CAPACITIES OF RAW, DRY-ROASTED, AND OIL-ROASTED PEANUTS
FROM 2005 TO 2007 CROP YEARS......................................................................110
3.1 Introduction.................................................................................................112
3.2 Materials and Methods................................................................................113
3.3 Results and Discussion...............................................................................121
4 PHENOLIC PROFILES OF PROCESSED PEANUT SKINS: ANTIOXIDANT,
RADICAL-SCAVENGING, AND BIOLOGICAL ACTIVITIES...........................141
4.1 Introduction.................................................................................................143
4.2 Materials and Methods................................................................................145
4.3 Results and Discussion...............................................................................151
5 CHROMATOGRAPHIC ISOLATION OF PHENOLIC ACIDS AND
PROANTHOCYANIDINS FROM DRY-BLANCHED AND DRY-ROASTED
PEANUT SKINS.......................................................................................................172
5.1 Introduction.................................................................................................174
5.2 Materials and Methods................................................................................176
5.3 Results and Discussion...............................................................................184
6 SUMMARY AND CONCLUSIONS........................................................................203
INDEX.........................................................................................................................................204
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LIST OF TABLES
Page
Table 3.1: Peanut kernel sample set (n = 15)..........................................................................131
total
Table 3.2: Lipid content and extraction (80% [v/v] methanol) yield of raw and processed peanut
kernels from 2005 to 2006 crop years.........................................................................131
Table 3.3: Effects of processing on the quantity of free p-coumaric acid and p-coumaric
derivatives in different peanut kernel types/cultivars from the 2006 crop..................132
Table 3.4: Total phenolic content (TPC) of raw and processed peanut kernels from 2005 to 2006
crop years....................................................................................................................133
Table 3.5: Oxygen radical absorbance capacity (ORAC -hydrophilic) of raw and processed
FL
peanut kernels from 2005 to 2006 crop years.............................................................134
Table 3.6: Photochemiluminescence (PCL -hydrophilic) of raw and processed peanut kernels
ACW
from 2005 to 2006 crop years......................................................................................135
Table 3.7: Trolox equivalent antioxidant capacity (TEAC) of raw and processed peanut kernels
from 2005 to 2006 crop years......................................................................................136
Table 4.1: TPC and TEAC of crude extracts (80% [v/v] acetone) and LMW fractions from dry-
blanched (DB) and dry-roasted (DR) peanut skins.....................................................163
Table 5.1: TPC, ORAC , and TEAC of crude extracts (80% [v/v] acetone) and HMW tannin
FL
fractions from dry-blanched (DB) and dry-roasted (DR) peanut skins.......................194
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