FACTORS RESPONSIBLE FOR FLAVOR AND OFF-FLAVOR DEVELOPMENT IN PECANS By Charles John Rudolph, Jr. II I Bachelor of Arts Austin Col Jege Sherman, Texas 1966 Submitted to the Faculty of the Graduate College of the Oklahoma State University in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY May, I 97 I J'),es ,'s 1q1 ID R q11f cop· :2.. ·, . FACTORS RESPONSIBLE FOR FLAVOR AND OFF-FLAVOR DEVELOPMENT IN PECANS ' ...,, Thesis Approved: ii ACKNOWLEDGMENTS The author gratefully acknowledges the counseling, encouragement, and patience of his major professor, Dr. George V. Odell, during the course of these studies and in the preparation of this thesis. He also acknowledges Dr. Michael E. Mason for providing the initial impetus in this work. Thanks are extended to Dr. G. R. Waller, Dr. E. D. Mitchell, Dr. S. Scheppele, Dr. G. W. Todd, and Mr. H. Hinrichs for their sug­ gestions. A special thanks is extended to Robert Roe, Jr., an excellent chemist and a better teacher, for continually encouraging and challeng­ ing the author throughout his endeavors in the field of chemistry. The author also thanks Dr. W. B. Guerrant, Jr. for counseling, advice, and encouragement during his undergraduate instruction. The author would like to thank: Keith Kinneberg for mass spectro­ meter services; Mike McGeehon, Mrs. Mabel Cardell ino, Mrs. Connie Horn, and Miss Ann Waller for their technical assistance; Wayne Adkins, for scientific glass blowing; Troy Barnes, for electronic repairs; Miss Trish Kelly and Miss Mary Reed for having mass spectra drawn; and Mrs. Barbara Lafon for computer programming consultation. The author extends a very special thanks to his wife, Diana, for her encouragement, understanding and assistance during the years of undergraduate and graduate study. The author also wishes to thank his parents, Mr. and Mrs. Charles J. Rudolph, for their encouragement and assistance, both financial and otherwise, in the author's educational iii pursuit which ultimately made this thesis possible. Finally the author would like to thank the Campbell Soup Company for their four year fellowship. He is also indebted to the Oklahoma . State University Biochemistry Department for facilities and financial support during these investigations. iv TABLE OF CONTENTS Chapter Page I • INTRODUCTION I I • LITERATURE REVIEW 3 I I I. NATURAL FLAVOR OF PECANS 6 Introduction 6 Reagents and Apparatus 6 Reagents . 6 Apparatus 6 Procedures 8 High Vacuum Falling Film Flash Evaporation 8 Transferring Volatiles Directly to a GLC Column 8 Steam Distillation • . • • • • 12 Sweeping Volatiles • • . • . • . • . • 12 Pecan Aroma From Skin and Hull Wastes 16 Vacuum Sublimation • 16 Results and Discussion 18 High Vacuum Technique--Fall ing Film Flash Evaporation • • • • • •••• 18 Steam Distillation •.••••••.• 19 Sweeping ..••••.•.....•.• 19 Pecan Aroma From Skin and Hull Wastes •••••• 20 Vacuum Subl Imation • 24 Summary • 41 IV. ROASTED FLAVOR • 42 Introduction 42 Reagents and Apparatus 43 Reagents • 43 Apparatus 43 Procedures 43 Roasting Pecans 43 v Chapter Page Volatile Collection Using High Vacuum Techniques • 43 Fractionation of Volatiles • . • • • • • 44 Roasting Peanuts Under Nitrogen • • • • 47 Gas Chromatography--Mass Spectrometry 47 Results and Discussion 49 Analysis of the Basic Fraction 49 Analysis of the Neutral Fraction 57 Roasting Under Nitrogen in Search of Dihydropyrazines 65 Summary . 74 V. OXIDATION STUDIES OF PECAN OILS 75 Introduction 75 Reagents and Apparatus 81 Reagents • • 81 Apparatus • • • • 83 Procedures 84 Oxidation Studies 84 Decolorized Pecan Oil •••• 84 Thiobarbituric Acid Analyses 86 Fatty Acid Analyses 87 Tocopherol Analyses 90 Oil Determination 90 Protein Determination 90 Results and Discussion 90 Summary • 114 VI. TOCOPHEROLS 116 Introduction 116 Occurrence •• . 116 Ana 1ys is . • . 118 Antioxidant Activity . 119 Spectral Studies . 122 Reagents and Apparatus 122 Reagents • • . 122 Apparatus . 123 Procedures . 123 Results and Discussion . 129 vi Chapter Page Tocopherol Analysis and Identification • • • . 132 Mass Spectral Analyses--General Considerations • 137 Mass Spectral Fragmentation Pattern of ~-Tocopherol . • . • • . • • • . 146 Mass Spectral Fragmentation Pattern of y-Tocopherol • • . • • • . • • 150 Mass Spectral Fragmentation Pattern of a-Tocopherol ••.•••.•••• 152 Mass Spectral Fragmentation Pattern of a-Tocophery 1 Acetate . .•. 154 Summary 159 VI I. MATURITY •.. 160 Introduction 160 General Studies on Pecans . • • • 160 Maturity Studies on the Walnut . • • • . 161 Lipid Compositions of Several Species . • • • • . 161 Maturation and Fatty Acid Synthetic Enzymes 164 Hereditary and Environmental Effects • 164 Apparatus and Reagents 165 Fatty Acid Analyses 165 Tocopherol Analyses 165 Procedures 165 Fatty Acid Analyses 165 Tocopherol Analyses . 165 Preparative Gas Chromatography of Fatty Acid Methyl Esters •••• 166 Results and Discussion 166 Fatty Acid Composition • 166 Fatty Acid Variations During Maturation 173 Percent Oil and Maturity .. 184 Tocopherol Variations During Maturation 184 Summary 188 VI I I • SUMMARY 192 SELECTED BIBLIOGRAPHY •. 194 APPENDIX A - FATTY ACID ANALYSES 203 APPENDIX B - COMPUTER PROGRAMS 209 . vi i Chapter Page APPENDIX C - MASS SPECTRA OF NITROGEN-CONTAINING COMPOUNDS, REFERENCE STANDARDS • • . • • • • • • • . • • • • • • 212 APPENDIX D - MASS SPECTRA OF OXYGEN-CONTAINING COMPOUNDS 216 vi i i LI ST OF TABLES Table Page I. Summary of Compounds Tentatively Identified From Raw Pecans by Combination Gas Chromatography--Mass Spectrometry . • • • • . • . 40 11. Summary of Compounds Identified in the Basic Fraction of Roasted Pecans . 58 111. Summary of Compounds Identified From Peanuts Roasted Under a Nitrogen Atmosphere . 73 IV. Keeping Time (Days),% Oleic Acid,% Linoleic Acid, Tocopherol Concentration ( µg/gm Oil), and% Protein in 70 Varieties of Pecans • • • • • • • • • • • • • • • 103 V•. Keeping Times, Theoretical, Actual, and Calculated, and the Difference Between Actual and Calculated Keeping Times for 70 Varieties • • • • • • • . • • • • . • 110 VI. Relative Retention Times and Molecular Ions of Tocopherols and Unknowns in the Non-Saponifiable Lipid Fraction of Pecan 0 i l • • • • • • • • • • • • • • • . • • • . 133 VI I. Metastable Transitions in Tocopherol Mass Spectra 149 VI I I. Comparison of Fatty Acid Distributions in Nine Varieties of Pecans Over a Four Year Period • • • . • • • • • • • • 174 IX. Fatty Acid Analyses of 12 Varieties of Pecans,. 1967 Crop •• 204 X. Fatty Acid Analyses of 63 Varieties of Pecans, 1968 Crop • • 205 XI. Fatty Acid Analyses of 83 Varieties of Pecans, 1969 Crop 20v XII. Computer Program 1 . 210 XI I I. Computer Program I I 211 ix LIST OF FIGURES · Figure Page 1. Falling Film Flash Evaporator with Recirculating Pump 9 2. Falling Film Flash Evaporator 10 3. Transfer of Volatiles Directly From a Trap to a GLC Column • 11 4. Combination Trap and GLC Flash Heater 13 5. Steam Distillation Apparatus •• 14 6. Apparatus for Trapping Volatiles Swept From Pecans 15 7. Vacuum Sublimation-Distillation Apparatus 17 8. Combination Gas Chromatographic--Mass Spectrometric Analy~Js of Flavor Components Obtained From Pecan Skins • . • . • • • 21 9. Combination Gas Chromatographic--Mass Spectrometric Analysis of the Volatile Components From Raw Pecans . • • • 25 10. Combination Capillary Column Gas Chromatographic--Mass Spectrometric Analysis of the Volatile Components From Raw Pecans . • • . • . • . • . 28 11. Apparatus for the Isolation of Flavor Components From Roasted Pecans . • . • . • ••. 45 12. Flow Diagram of the Fractionation Process 46 13. Apparatus for Roasting Under a Nitrogen Atmosphere 48 14. Combination Gas Chromatographic--Mass Spectrometric Analysis of the Components of the Basic Fraction of the Volatile Components From Roasted Pecans . • • . • . 50 15. Combination Gas Chromatographic--Mass Spectrometric Analysis of the Components of the Neutral Fraction of the Volatile Components From Roasted Pecans • • • • • • • . • • • • . 59 16. Mass Spectra of Three Dihydropyrazines and Each Corresponding Pyrazine . 66 x Figure Page 17. Combination Gas Chromatographic--Mass Spectrometric Analysis of the Volatile Components From Peanuts Roasted Under Ni t roge n • . • • • • . • • • • • 68 18. Graphical Scheme for Fatty Acid Oxidation 76 19. Sample Calculation of the Keeping Time of a Pecan Oil 85 20. Gas Liquid Chromatographic Analysis of the Fatty Acids From Pecan Oils • . • . • • • • 88 21. Chemical Changes During the Oxidation of a Pecan Oil . 92 22. Comparison of the Oxidative Stabilities of Pecan Oi Is 95 23. Changes in the Tocopherol Concentrations During Oxidation of Pecan 0 i I s . • . • . • • . • . • • . 96 24. Changes in Pigmentation During Oxidation of Pecan Oils 97 25. Changes in Oleic/Linoleic Ratio During Oxidation of Pecan 0 i 1s . • . • 99 26. Effect of y-Tocopherol on Olis With Relatively High and Low Concentrations of Linoleic Acid • . • . • • . • • •••. IOI 27. Variation of Keeping Time With the% Linoleic Acid 104 28. Variation in Keeping Time With% Oleic Acid 105 29. Complementary Relationship Between Oleic and Linoleic Acid Composition . • • • • • • • • • 106 30. Relationship Between Tocopherol Content and Keeping Time 107 31. Relationship Between Tocopherol and Linoleic Acid Concentration • • • • • • . • . • 108 32. Relationship Between the Deviation of the Actual Keeping Time From the Calculated Keeping Time and Tocopherol Concentration • . • • . • • • • • • • • . • 112 33. Variation of Tocopherol Concentration With Keeping Time 113