AN ABSTRACT OF THE THESIS OF Theeranuch Chantrachit for the degree of Master of Science in Horticulture presented on December 1.1994 Title : Banana Quality : Flavor Volatiles under Anaerobic and Aerobic conditions. Abstract approved : . . fl Daryl G. Richardson Alcoholic off-flavor and accompanying volatile compounds produced by bananas (Cavendishii spp) held at 20oC and subjected to aerobic (air control treatment) or anaerobic conditions (nitrogen treatment) were compared by solid phase micro extraction (SPME), a newly developed method for volatile separation. In general, volatile production was suppressed under anaerobic conditions but resumed, to some extent, after fruits were returned to air. The effects of anaerobic conditions on individual compounds were separated into six groups based on their production trends relative to those of air conditions. It was clear that bananas subjected to anaerobic conditions produced ethanol that could be detected easily by SPME. Anaerobic conditions almost completely blocked the esterification step needed to produced normal volatile profiles of ripening bananas. The effects of anaerobic conditions on banana flavor and off-flavor development were determined by a taste panel quality scaling method. In order to determine the difference between bananas subjected to both conditions (aerobic and anaerobic), the "difference from control" method was used in other experiments. Generally, the bananas subjected to anaerobic conditions had better physical appearance than bananas in the air control group but lacked fruit flavor and firmness. Off-flavor developed to a greater extent in bananas under anaerobic conditions than those under the air control which had almost no off- flavor. The correlation between off-flavor and ethanol was very high (r = 0.87) while for other volatiles was very low. This finding implies that ethanol is probably the only volatile causing anaerobic off-flavor in ripening bananas. In order to confirm this, headspace ethanol was detected by SPME, and tissue ethanol was extracted and assayed enzymaticaily. The result showed that tissue ethanol was correlated with headspace ethanol (r2 = 0.66). The threshold for off-flavor development in ripening bananas was 300 mg of tissue ethanol /100 g FW or 0.5 ppm for headspace ethanol. Our results indicate that even three days in anaerobic conditions could injure ripening bananas. Thus unlike other fresh fruits, O2 levels at or below 1 % is not suitable for application as postharvest insect control treatment in ripening bananas. Banana Quality : Flavor Volatiles under Anaerobic and Aerobic Conditions by Theeranuch Chantrachit A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Completed December 1,1994 CommencementJune 1995 Master of Science thesis of Theeranuch Chantrachit presented on December 1. 1994 APPROVED: * »V " ' ~yf » «• ^ ■ ——-— Major Professo(jrepresenting Horticulture Chair of Department of Horticultk^ -*- Dean of GraduateiScjhool I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Theeranuch Chantrachit, Author ACKNOWLEDGMENTS I would like to express my sincere thanks to Dr. Daryl G. Richardson, my major professor, for his support, hospitality, encouragement, and friendship during my studies at Oregon State University. Without his guidance, I would never have completed my work. Special appreciation is also extended to my minor professor, Dr. Wilbert Gamble, and to all other committee members: Dr. Bemadine D. Strik and Dr. Gary D. Jolliff. Their constructive suggestions and comments have been very helpful in writing this thesis. Finally, I am grateful to my sponsor, the Royal Thai Government, for financially support my studies here. Special thanks goes to Kais Ebrahem and his wife, Khalidha. I would like to thank them for all their moral support, understanding, and encouragement. Ultimately, this feeling of appreciation is extended to all my friends and colleagues in the Horticulture Department. All of them have been extremely helpful to me. Being here has been one of the best times in my life. Finally, special thanks goes to my best friend, Suk Jaroenkit. With his encouragement and support, the thorough meaning of 'friend' is present. THE LORD BUDDHA NEVER TEACHES ONE TO RUN AWAY FROM THE WORLD OF SUFFERING, BUT ENCOURAGES ONE TO CONFRONT, UNDERSTAND, AND BE AWARE OF SUFFERING. ALSO HE TEACHES ONE TO FACE THE FACTS SO THAT HE WILL NO LONGER SUFFER. EVENTUALLY, ONE WILL BE ABLE TO SURVIVE ON THE EARTH, TO EAT WITHOUT DESIRE, AND TO LOVE WITHOUT ATTACHMENT. Yantra Amaro Bhikkhu. TABLE OF CONTENTS Page CHAPTER 1. INTRODUCTION AND LITERATURE REVIEW 1 Banana 3 Summary of botany 3 Nutritional and therapeutic values 4 Production and distribution 4 Maturity stage at harvest 5 Postharvest handling of bananas 6 Storage temperature 6 Ripening process 7 Physiological disorders 7 Chilling injury 7 Browning 8 Physiology and biochemistry of maturation 10 The respiratory climacteric 10 Banana ripening and biochemical changes 11 Fruit quality and fruit flavor 13 Fruit quality 13 Fruit flavor 13 The aroma of fruit 14 Biogenesis of fruit aroma 15 Banana volatiles 16 Production during ripening 16 Sensory aspect 17 Biogenesis of banana volatiles 18 Conversion of amino acids 19 Fatty acid metabolism 20 Enzymatic oxidative splitting of unsaturated fatty acid 20 TABLE OF CONTENTS (Continued) Page Controlled atmosphere (CA) and insect control 22 CA and banana 22 Anaerobic conditions and insect control 23 Off-flavor development 24 Anaerobic respiration and its products 25 Acetaldehyde 26 Ethanol 27 Solid phase microextraction (SPME) 28 CHAPTER 2. EFFECTS OF ANAEROBIC AND AEEROBIC RIPENING CONDITIONS ONPRODUCTION OF BANANA VOLATILE COMPOUNDS Abstract 30 Introduction 31 Materials and methods 33 Fruits and treatments preparation 33 Stages of ripening and changes in color 34 Sampling technique and headspace analysis ...34 GLC-FID conditions 35 GLC/MS conditions 35 CO2 and O2 measurement 36 Results 37 Volatile compounds of ripening bananas... 37 Effects of nitrogen treatments on banana volatiles 46 Effects on total volatile production 46 Effects on flavor impact compounds 51 Effects on individual volatile production 58 CO2 and O2 concentration 68 TABLE OF CONTENTS (Continued) Page Discussion 71 Banana volatiles 71 Effects of anaerobic conditions on volatile production 73 Literature cited 76 CHAPTER 3. EFFECTS OF ANAEROBIC CONDITIONS ON ETHANOL PRODUCTION CORRELATED TO OFF-FLAVOR DEVELOPMENT IN RIPENING BANANAS Abstract 82 Introduction 83 Materials and methods 86 Fruits and treatments preparation 86 Samples for headspace analysis 86 Samples for evaluation using scaling method and tissue ethanol 86 Samples for evaluation using 'difference from control' method 87 Sampling techniques and GLC conditions 87 Standard curves for relative peak area of ethanol and it esters.... 88 Tissue ethanol extraction 88 Scaling method for quality evaluation 89 'Difference from control' method for quality evaluation 90 Results .". 91 Total production of volatiles under anaerobic conditions 91 Production of ethanol and its corresponding esters 97 Tissue ethanol measurement 100 Fruit quality and flavor evaluation 108 Scaling method 108 'Difference from control' method 115 TABLE OF CONTENTS (Continued) Page Discussion 116 Effects of anaerobic conditions on ethanol production 116 Effects of anaerobic conditions on fruit quality 117 Correlation between off-flavor and volatile compounds 119 Correlation between headspace ethanol and it corresponding esters 120 Literature cited 123 CONCLUSIONS 130 BIBLIOGRAPHY 133 APPENDIX 147