Ildrød Pigeon”
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DEPARTMENT OF FOOD SCIENCE POPIELARZ JOLANTA MARTA faculty of life sciences PhD THESIS 2012 · ISBN 978-87-7611-491-6 university of copenhagen MARTA JOLANTA POPIELARZ The effect of ethylene inhibition on ”Ildrød Pigeon” apple quality and aroma profile T he effect of ethylene inhibition on he effect of ethylene The Effect of Ethylene Inhibition on ”Ildrød Pigeon” Apple Quality and Aroma Profile ” I ldrød ldrød PHD THESIs · 2012 Marta Jolanta Popielarz P igeon” apple quality and aroma profile apple quality and aroma The effect of ethylene inhibition on ‘Ildrød Pigeon’ apple quality and aroma profile Ph.D. Thesis by Marta Jolanta Popielarz Under supervision of: Mikael Agerlin Petersen Torben Bo Toldam-Andersen Department of Food Science Faculty of Life Sciences University of Copenhagen January 2012 The effect of ethylene inhibition on ”Ildrød Pigeon” apple quality and aroma profile Ph.D. Thesis 2012 @ Marta Jolanta Popielarz ISBN 978-87-7611-491-6 Printed by SL grafik, Frederiksberg C, Denmark (www.slgrafik.dk) 2 Many of life's failures are men who did not realize how close they were to success when they gave up. Thomas Edison 3 4 Preface This Ph.D. project has been conducted in the Quality and Technology research group at the Department of Food Science, University of Copenhagen. Therefore grateful acknowledge goes to the University of Copenhagen for the funding sources that made my Ph.D. work possible. Ph.D. project was carried under supervision of Mikael Agerlin Petersen and Torben Bo Toldam-Andersen. Mikael, thank you for sharing your ‘aroma’ experience with me. You were always organized and ready to help. The dissuasions with you were eyes opening, productive and inspiring. Thank you for your interest in my life and the help you showed during ‘financial crises’. Torben, your advices and comments were always interesting and stimulating. Thank you for being direct and straight to the point at our meetings. Thank you for your time, which you spent on reading and ‘tables/figures’ check out. To both, Mikael and Torben, I send you my gratitude for the patience and the encouragement you have given me. The members of the Quality and Technology research group have contributed immensely to my personal and professional time in Copenhagen. The group has been a source of friendships as well as good advice and collaboration. Lina, thank you for time we have spent together; both at and out of the university. It was comforting to discuss life issues with you during ‘the balcony breaks’. I am grateful to Margaret for proof reading of the manuscript and also for being a good friend. Anders, thank you for a nice atmosphere in our office and for your ‘jokes’ - you remain ‘the funniest guy in the world’. Frans, thank you for your magic powers - meaning statistic support and most of all for your patience. Jose, thank you for being a great colleague, who was always ready to listen and explain whatever needed. Abdel (my ethylene man) and Christina (my handyman lady), thank you for your great lab help – I promise to improve my baking skills. There is also a group of great people, who work/-ed in Pometet, experimental orchard in Taastrup. Henrik, Steen, Carsten and Lisbet - thank you for Danish lessons, very positive attitude and your friendly interest in my work and life. For the dissertation, I would like to thank my committee members: Renate Müller, Marek Gajewski and Merete Edelenbos for their time and interest. Finally yet importantly, I would like to thank my family and close friends, both in Poland and Denmark, for all their encouragement. For my mother Basia and grandma Stasia, who raised me with love and supported me in all my pursuits. Moreover, most of all for my loving, supportive, encouraging, and patient Carsten, whose faithful support during the final stages of this Ph.D. is so appreciated. Thank you All Marta Jolanta Popielarz January 2012 5 6 SUMMARY In recent decades, producers have observed an increasing trend of consumer demands for high quality stored apples. Apple quality involves many aspects including external appearance (color), as well as internal parameters namely firmness and flavour (taste and aroma). Development of suitable pre- and postharvest management that improves and maintains quality is a challenge. The objective of the presented thesis is to explore the practical approach to optimize horticultural management, and thus to ensure better overall apple quality after storage. ‘Ildrød Pigeon’ is a Danish apple cultivar, which market potential strongly depends on its distinct red color and characteristic flavour. There is however, no available literature about ‘Ildrød Pigeon’ aroma profile and only a little about changes in quality depending on horticultural practices. ‘Ildrød Pigeon’ apples are traditionally exposed to light for up to 2-3 weeks after harvest to ensure development of fruit red skin color. The length of light exposure is critical as apples can be sunburn, become overripe or even rotten, and firmness is strongly reduced. These exposed apples have impaired storability as they reach storage already very ripe. The registration of the ethylene inhibitor SmartFresh® (1-MCP, 1-methylcyclopropene) in Denmark opened new alternatives to preserve apple quality and storability. 1-MCP binds to ethylene receptors and restrains ethylene action. This in turns affects ripening related processes like; color changes, softening, starch degeneration to sugar, acid degradation and aroma development. 1-MCP has been considered a “magic bullet” in postharvest technology as apple quality is maintained during storage, especially firmness. However, the suppression of aroma production, which contributes most to apple flavour, is one of 1- MCP drawbacks. The experiments included in this PhD thesis were conducted to explore a range of the most important horticultural factors that affect final apple quality. Consequently, an optimized postharvest management is proposed with revised harvest time, new 1-MCP timing application and shorter light exposure period. As the outcome, apples with better quality and improved market potential were obtained. The color, ethylene production, aroma profile and firmness, which are ‘Ildrød Pigeon’ major quality contributors, were most important parameters in the experiments. Outline of the thesis. The PhD thesis consists of 11 chapters; Chapters 1-4 present an overview of already existing knowledge about apple physiological processes, especially during ripening. The role of ethylene in ripening, existing ethylene inhibitors and their properties are also described. Chapter 5 refers to the popular ethylene inhibitor (1-MCP), describes its influence on apple quality parameters and includes a short explanation of the registration of the inhibitor in Denmark. Chapter 6 introduces ‘Ildrød Pigeon’ as an apple variety with its traditional postharvest handling. GC-olfactometry technique and the detection frequency methods are described, 7 as they were used to identify ‘Ildrød Pigeon’ characteristic aroma compounds. Twelve aroma compounds (esters, aldehydes and alcohols) were identified as having the greatest impact on the overall flavour of the ‘Ildrød Pigeon’ apples. Chapter 7 describes the effects of pre-harvest factors; mainly thinning practice (cropping level) and nitrogen fertilization, on ‘Ildrød Pigeon’ fruit growth and quality after storage. Maturity was delayed in the apples from non-fertilized trees as they had low ‘fruit under’ to ‘fruit on the tree’ ratio and low ethylene production after storage. Ethylene production decreased with higher crop load. Hand thinning practice led to an 8.4% increase in fruit size. There was also positive effect of nitrogen on apple size. Most of the principal aroma compounds were insensitive to nitrogen levels, however hexanal, 2-methyl-2-pentenal and isomer forms of 2,4-hexadienal had higher production in apples fertilized with moderate nitrogen level, while ethyl acetate and 1-heptanol were produced at the highest level in apples fertilized with high nitrogen. In chapter 8 the optimal length for ripening recovery after storage has been established between 5 to 8 days. The appropriate time at room temperature after cold storage is needed mostly to accelerate ripening and to enhance aroma development to meet consumer’s quality demands. The effects of harvest time, storage length in combination with 1-MCP treatment were described in chapter 9. The commercially harvested ‘Ildrød Pigeon’ apples seem to represent post-climacteric ripening stage; with decline ethylene concentration and lower firmness. 1-MCP application on those apples was not effective as its application after harvest was done when ethylene production already accelerated. Longer storage positively affected regeneration of volatile compounds. Harvest of ‘Ildrød Pigeon’ apples should be done earlier to delay the ethylene formation so that 1-MCP application can give anticipated responds. Chapter 10 describes effects of postharvest light exposure combined with different timing of 1-MCP application on external and internal quality parameters. Due to ‘Ildrød Pigeon’ progressive softening during postharvest handling, it was desirable to optimize postharvest practice in a way, which assures adequate color development with a shorter postharvest sunlight exposure to achieve the better quality fruit. The main coloration occurred between day 2 and 4 of the light exposure. Color changes were inhibited by early 1-MCP application. Finally, sunlight exposure time was proposed to be shortened to an average of 8 days, after