LLoouuiissiiaannaa SSttaattee UUnniivveerrssiittyy LLSSUU DDiiggiittaall CCoommmmoonnss LSU Doctoral Dissertations Graduate School 2006 PPhheennoolliicc ccoommppoossiittiioonn aanndd aannttiiooxxiiddaanntt aaccttiivviittyy ooff sswweeeettppoottaattooeess [[IIppoommooeeaa bbaattaattaass ((LL..)) LLaamm]] Malkeet Singh Padda Louisiana State University and Agricultural and Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_dissertations RReeccoommmmeennddeedd CCiittaattiioonn Padda, Malkeet Singh, "Phenolic composition and antioxidant activity of sweetpotatoes [Ipomoea batatas (L.) Lam]" (2006). LSU Doctoral Dissertations. 1327. https://digitalcommons.lsu.edu/gradschool_dissertations/1327 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Doctoral Dissertations by an authorized graduate school editor of LSU Digital Commons. For more information, please [email protected]. PHENOLIC COMPOSITION AND ANTIOXIDANT ACTIVITY OF SWEETPOTATOES [IPOMOEA BATATAS (L.) LAM] A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Department of Horticulture by Malkeet Singh Padda B.S., Punjab Agricultural University, 1998 M.S., Punjab Agricultural University, 2001 May 2006 ACKNOWLEDGMENTS I am deeply grateful to Dr. David Picha for his patience, perfection, guidance, and encouragement. I would also like to thank my committee, Dr. Don Labonte, Dr. Paul Wilson, Dr. Charles Johnson, Dr. Jack Losso, Dr. Zhimin Xu for their useful input during my research. My special thanks to Gloria McClure for her technical assistance, suggestions, and motivation to achieve my goal. Exceptional thanks to my wife ‘Kamal’ for all her love, support, and understanding. Thanks for being such a wonderful person in my life. I would also like to thank my family in India for their continue encouragement and best wishes. Thanks to all my friends, in particular Gillz, Bazwaz, Josanz, and Kahlonz, for their support at every moment of life. Especially, I would like to thank Mehak, Aman, and Jatinder for such a wonderful surprise celebration after my defense. Above all, I want to thank my parents for all their hard work, sacrifices and prayers for my success. I can never repay all they have done for me. ii TABLE OF CONTENTS ACKNOWLEDGMENTS..................................................................................................ii LIST OF TABLES.............................................................................................................vi LIST OF FIGURES.........................................................................................................viii ABSTRACT........................................................................................................................x CHAPTER 1. INTRODUCTION.......................................................................................1 NUTRITIONAL IMPORTANCE..................................................................................2 PHENOLICS IN SWEETPOTATO...............................................................................3 REFERENCES...............................................................................................................6 CHAPTER 2. METHOD DEVELOPMENT......................................................................9 INTRODUCTION..........................................................................................................9 MATERIALS AND METHODS..................................................................................12 Reagents....................................................................................................................12 Plant Material............................................................................................................12 Sample Preparation and Tissue Extraction...............................................................12 Total Phenolics..........................................................................................................13 Individual Phenolic Acids.........................................................................................14 Statistical Analysis....................................................................................................15 RESULTS AND DISCUSSION...................................................................................15 Extraction Solvents...................................................................................................15 Total Phenolics..........................................................................................................15 Individual Phenolic Acids.........................................................................................17 Method Validation....................................................................................................25 REFERENCES.............................................................................................................26 CHAPTER 3. ANTIOXIDANT ACTIVITY AND PHENOLIC COMPOSITION CHANGES IN SWEETPOTATO ROOT AND LEAF TISSUE AT DIFFERENT GROWTH STAGES.........................................................................................................28 INTRODUCTION........................................................................................................28 MATERIALS AND METHODS..................................................................................29 Reagents....................................................................................................................29 Plant Material............................................................................................................30 Tissue Preparation.....................................................................................................30 Tissue Extraction......................................................................................................30 Total Phenolics..........................................................................................................31 Antioxidant Activity.................................................................................................31 Individual Phenolic Acids.........................................................................................32 Statistical Analysis....................................................................................................32 RESULTS AND DISCUSSION...................................................................................33 Total Phenolics..........................................................................................................33 Antioxidant Activity.................................................................................................35 Individual Phenolic Acids.........................................................................................36 CONCLUSIONS..........................................................................................................39 iii REFERENCES.............................................................................................................39 CHAPTER 4. PHENOLIC ACID COMPOSITION AND ANTIOXIDANT ACTIVITY OF PROCESSED SWEETPOTATOES...........................................................................42 INTRODUCTION........................................................................................................42 MATERIALS AND METHODS..................................................................................44 Reagents....................................................................................................................44 Plant Material............................................................................................................44 Tissue Preparation and Extraction............................................................................44 Total Phenolics..........................................................................................................45 Antioxidant Activity.................................................................................................45 Individual Phenolic Acids.........................................................................................46 Statistical Analysis....................................................................................................46 RESULTS AND DISCUSSION...................................................................................47 Total Phenolics..........................................................................................................47 Antioxidant Activity.................................................................................................48 Individual Phenolic Acids.........................................................................................49 CONCLUSIONS..........................................................................................................51 REFERENCES.............................................................................................................52 CHAPTER 5. EFFECT OF LOW TEMPERATURE STORAGE ON PHENOLIC COMPOSITION AND ANTIOXIDANT ACTIVITY OF SWEETPOTATOES............55 INTRODUCTION........................................................................................................55 MATERIALS AND METHODS..................................................................................56 Reagents....................................................................................................................56 Plant Material............................................................................................................57 Tissue Preparation and Extraction............................................................................57 Total Phenolics..........................................................................................................58 Antioxidant Activity.................................................................................................58 Individual Phenolic Acids.........................................................................................59 Statistical Analysis....................................................................................................60 RESULTS AND DISCUSSION...................................................................................60 Total Phenolics..........................................................................................................60 Antioxidant Activity.................................................................................................63 Individual Phenolic Acids.........................................................................................65 CONCLUSIONS..........................................................................................................68 REFERENCES.............................................................................................................69 CHAPTER 6. PHENOLIC COMPOSITION AND ANTIOXIDANT ACTIVITY OF MINIMALLY PROCESSED SWEETPOTATOES.........................................................71 INTRODUCTION........................................................................................................71 MATERIALS AND METHODS..................................................................................72 Reagents....................................................................................................................72 Tissue Preparation.....................................................................................................73 Headspace Gas Composition....................................................................................73 Tissue Extraction......................................................................................................73 Total Phenolics..........................................................................................................74 Antioxidant Activity.................................................................................................74 iv Individual Phenolic Acids.........................................................................................75 Statistical Analysis....................................................................................................75 RESULTS AND DISCUSSION...................................................................................76 Headspace Gas Composition....................................................................................76 Total Phenolics..........................................................................................................77 Antioxidant Activity.................................................................................................79 Individual Phenolic Acids.........................................................................................80 CONCLUSIONS..........................................................................................................82 REFERENCES.............................................................................................................82 CHAPTER 7. PHENOLIC COMPOSITION AND ANTIOXIDANT ACTIVITY OF SWEETPOTATO CULTIVARS......................................................................................85 INTRODUCTION........................................................................................................85 MATERIALS AND METHODS..................................................................................86 Reagents....................................................................................................................86 Plant Material............................................................................................................86 Tissue Preparation and Extraction............................................................................86 Total Phenolics..........................................................................................................87 Antioxidant Activity.................................................................................................87 Individual Phenolic Acids.........................................................................................88 Statistical Analysis....................................................................................................89 RESULTS AND DISCUSSION...................................................................................89 Total Phenolics and Antioxidant Activity.................................................................89 Individual Phenolic Acids.........................................................................................90 CONCLUSIONS..........................................................................................................92 REFERENCES.............................................................................................................93 CHAPTER 8. SUMMARY...............................................................................................95 VITA.................................................................................................................................98 v LIST OF TABLES Table 2.1. Comparison of different solvents for extraction of total phenolics in sweetpotato root tissue..........................................................................................16 Table 2.2. The effect of number of extraction steps (using 80% methanol as solvent) on recovery of total phenolics in sweetpotato root tissue.......................16 Table 2.3. Analytical characteristics and method validation data for HPLC using a Gemini 5 µm, 4.6 × 250 mm column....................................................................25 Table 2.4. Analytical characteristics and method validation data for HPLC using a Gemini 3 µm, 4.6 × 150 mm column....................................................................26 Table 3.1. Mean values of weight and size (diameter) of five sweetpotato roots at different growth stages..........................................................................................30 Table 3.2. Individual phenolic acid content in sweetpotato root tissues at different growth stages........................................................................................................38 Table 3.3. Individual phenolic acid content in sweetpotato leaf tissues at different growth stages........................................................................................................38 Table 4.1. Total phenolics in raw and processed sweetpotato root tissues.......................47 Table 4.2. Antioxidant activity in raw and processed sweetpotato root tissues...............48 Table 4.3. Individual phenolic acid content in raw and processed sweetpotato skin tissue.....................................................................................................................50 Table 4.4. Individual phenolic acid content in raw and processed sweetpotato cortex tissue..........................................................................................................50 Table 4.5. Individual phenolic acid content in raw and processed sweetpotato pith tissue.....................................................................................................................50 Table 5.1. Total phenolics in different tissues of non-cured sweetpotato roots at different intervals of storage at 5 °C, including transfer to ambient temperature (22 °C) for an additional 3 days (d)..................................................62 Table 5.2. Antioxidant activity in different tissues of non-cured sweetpotato roots at different intervals of storage at 5 °C, including transfer to ambient temperature (22 °C) for an additional 3 days (d)..................................................64 Table 5.3. Chlorogenic acid content in different tissues of non-cured roots sweetpotato roots at different intervals of storage at 5 °C, including transfer to ambient temperature (22 °C) for an additional 3 days (d)...................67 vi Table 5.4. Caffeic acid content in different tissues of non-cured roots sweetpotato roots at different intervals of storage at 5 °C, including transfer to ambient temperature (22 °C) for an additional 3 days (d)..................................................67 Table 5.5. 4,5-dicaffeoylquinic acid content in different tissues of non-cured roots sweetpotato roots at different intervals of storage at 5 °C, including transfer to ambient temperature (22 °C) for an additional 3 days (d)...................67 Table 5.6. 3,5-dicaffeoylquinic acid content in different tissues of non-cured roots sweetpotato roots at different intervals of storage at 5 °C, including transfer to ambient temperature (22 °C) for an additional 3 days (d)...................68 Table 5.7. 3,4-dicaffeoylquinic acid content in different tissues of non-cured roots sweetpotato roots at different intervals of storage at 5 °C, including transfer to ambient temperature (22 °C) for an additional 3 days (d)...................68 Table 6.1. Total phenolics and antioxidant activity in minimally processed sweetpotatoes stored at 0 and 5 °C for 4 and 8 days.............................................78 Table 6.2. Individual phenolic acid accumulation during storage of minimally processed sweetpotatoes.......................................................................................81 Table 7.1. Total phenolics and antioxidant activity of different sweetpotato cultivars and breeding lines..................................................................................89 Table 7.2. Individual phenolic acid content of different sweetpotato cultivars and breeding lines........................................................................................................91 vii LIST OF FIGURES Figure 1.1. Biosynthetic pathways for production of chlorogenic acid and isochlorogenic acid (Friedman, 1997)....................................................................4 Figure 1.2. Molecular structures of phenolic compounds in sweetpotato tissues (cv. Ayamurasaki). diCQA: dicaffeoylquinic acid; triCQA: tricaffeoylquinic acid (Islam et al., 2003)...............................................................5 Figure 2.1. Absorbance of standard solutions measured with FDR (Folin-Denis reagent) and FCR (Folin-Ciocalteu reagent).........................................................17 Figure 2.2. A representative chromatogram for a 20 µl sweetpotato extract analyzed with a Gemini C18, 5 µm, 4.6 × 250 mm column using a mobile phase consisting acetonitrile: 10 mM K HPO (20:80), pH 2.6; flow rate: 2 4 0.75 ml/min, temperature: 30 °C, UV detection at 320 nm..................................19 Figure 2.3. A representative chromatogram for a 20 µl sweetpotato extract analyzed with a Gemini C18, 5 µm, 4.6 × 250 mm column using a mobile phase consisting methanol: 33 mM phosphate buffer (40:60), pH 3.0; flow rate: 0.75 ml/min, temperature: 30 °C, UV detection at 320 nm..........................20 Figure 2.4. A representative chromatogram for a 20 µl sweetpotato extract analyzed with a Gemini C18, 5 µm, 4.6 × 250 mm column using a mobile phase consisting 1% (v/v) formic acid in aqueous solution: acetonitrile: 2- propanol (70:22:8), pH 2.5; flow rate: 0.75 ml/min, temperature: 30 °C, UV detection at 320 nm........................................................................................21 Figure 2.5. A representative chromatogram for a 20 µl sweetpotato extract analyzed with a Gemini C18, 3 µm, 4.6 × 150 mm column using a mobile phase consisting 1% (v/v) formic acid in aqueous solution: acetonitrile: 2- propanol (70:22:8), pH 2.5; flow rate: 0.75 ml/min, temperature: 30 °C, UV detection at 320 nm........................................................................................22 Figure 2.6. A representative chromatogram for a 20 µl sweetpotato extract analyzed with an Alltima C18 Rocket, 3 µm, 7 × 53 mm column using a mobile phase consisting 1% (v/v) formic acid in aqueous solution: acetonitrile: 2-propanol (70:22:8), pH 2.5; flow rate: 0.75 ml/min, temperature: 30 °C, UV detection at 320 nm........................................................23 Figure 2.7. A representative HPLC chromatogram for a 20 µl sweetpotato extract analyzed with a Novapak C18, 4 µm, 3.9 × 150 mm column using a mobile phase consisting 1% (v/v) formic acid in aqueous solution: acetonitrile: 2-propanol (70:22:8), pH 2.5; flow rate: 0.75 ml/min, temperature: 30 °C, UV detection at 320 nm........................................................24 Figure 3.1. Total phenolics in sweetpotato root tissues at different growth stages..........33 viii Figure 3.2. Total phenolics and antioxidant activity of sweetpotato leaf tissue at different growth stages..........................................................................................34 Figure 3.3. Antioxidant activity in sweetpotato root tissues at different growth stages.....................................................................................................................35 Figure 3.4. Comparison of HPLC chromatograms for individual phenolic acids isolated from young leaf tissue and cortex tissue (stage I)...................................37 Figure 4.1. Correlation between antioxidant activity and total phenolics in sweetpotato root tissues........................................................................................49 Figure 5.1. Total phenolics in cured and non-cured sweetpotato roots at different intervals of storage at 5 °C....................................................................................61 Figure 5.2. Antioxidant activity of cured and non-cured sweetpotato roots at different intervals of storage at 5 °C.....................................................................63 Figure 5.3. Correlation between total phenolics (TP) and antioxidant activity (AA) in non-cured sweetpotato roots during 4 weeks of storage at 5 °C.......................65 Figure 6.1. Changes in headspace O levels in minimally processed sweetpotatoes 2 stored during storage at 0 °C (A) and 5 °C (B).....................................................76 Figure 6.2. Changes in headspace CO levels in minimally processed 2 sweetpotatoes stored during storage at 0 °C (A) and 5 °C (B).............................77 ix