i Effect of variety, harvest and storage time, defoliation and nitrogen application on the physical and biochemical properties of potato tubers in relation to bruise susceptibility Regiane Scharf Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Food Science and Nutrition October, 2014 ii The candidate confirms that the work submitted is her own and that appropriate credit has been given where reference has been made to the work of others. This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. © 2014 The University of Leeds and Regiane Scharf iii Publications List of accepted abstracts Scharf, R., Watson, N., McManus, C., Orfila, C., Povey, M. J. W. and Ho, P. 2012. Assessment of potato bruising. Sutton Bridge Storage Day, 29 November 2012, Sutton Bridge, UK. Scharf, R., Orfila, C. and Ho, P. 2013. Extraction of ‘free’ and ‘trapped’ phenolics from potato fibre. Industry day, 14 January 2013, Leeds, UK. Scharf, R., Orfila, C. and Ho, P. 2013. Effect of harvest period on the mechanical properties and microstructure of potatoes. ESPCA/São Paulo School of Advanced Science, Advances in Molecular Structuring of Food Materials, 1-5 April 2013, Pirassununga, Brazil. Scharf, R. and Orfila, C. 2013. Cell wall microstructure of potato cortex tissue and correlations with bruise susceptibility upon harvest and storage. The XIIIth Cell Wall Meeting, 7-12 July 2013, Nantes, France. Scharf, R. 2013. The relationship between bruising index, tuber deformability and composition of phenolic acids. AHDB Crop Research Conference, 25 September 2013, London, UK. Scharf, R., Ho, P., Maycock, J. and Orfila, C. 2014. The effect of variety, defoliation, application of nitrogen, harvest and storage on bruising incidence of potato tubers. 50 years of Storage Research, 3 July 2014, Sutton Bridge, UK. Acknowledgements Watson, N., Povey, M., Corona, E, Benedito, J. and Parker, N. 2012. Acoustic microscopy in the food industry. International Symposium on Ultrasound in the Control of Industrial Processes (UCIP 2012). IOP Publishing IOP Conf. Series: Materials Science and Engineering, 42. iv List of papers produced (manuscripts in preparation) Scharf, R., Ho, P., Maycock, J. and Orfila, C. 2014. Characterization of potato cell wall sugars by HPAEC-PAD: enhancing extraction and analysis. In preparation. Scharf, R., Ho, P., Maycock, J. and Orfila, C. 2014. Extraction of ‘free’ and ‘trapped’ phenolics from potato fibre. In preparation. Scharf, R., Ho, P., Maycock, J. and Orfila, C. 2014. The effect of variety, harvest and storage on bruising incidence of potato tubers. In preparation. Scharf, R., Ho, P., Maycock, J. and Orfila, C. 2014. The effect of variety, harvest and defoliation on bruising incidence of potato tubers. In preparation. Scharf, R., Ho, P., Maycock, J. and Orfila, C. 2014. A comparison of methods to assess bruising of potato tubers. In preparation. v “The potato is on the frontline in the fight against world hunger and poverty.” Jacques Diouf Director-General FAO from 1994 to 2011 vi Acknowledgements First and foremost, praises and thanks to the Lord, the Almighty, for His showers of blessings throughout my research work to complete the research successfully. I would like to thank for the help and support of the kind people around me, to only some of whom it is possible to give particular mention here. I deeply acknowledge my supervisors, Dr Caroline Orfila, Dr Peter Ho and Dr Joanne Maycock, for having trusted in my ability to complete this project successfully. I am grateful to Dr Orfila, my main supervisor, for having invited me to start a PhD and for having supported this decision. I thank her for providing the invaluable guidance throughout this research, especially for having taught me how to report my work in an interesting and successful way. I also wish to express my deepest gratitude to Dr Ho, my collaborative supervisor, for having been so supportive, dedicating me his time whenever I needed his advice. Dr Maycock, my third supervisor, for her encouragement and good advice on writing. To my external supervisor, Dr Sue Cowgill, for her support and excellent advice. Undoubtedly, it was a great privilege and honour to work and study under my supervisors guidance. I would like to thank the British Potato Council and the Yorkshire Agricultural Society for funding, Cambridge University farm, namely Dr Mark Stalham and Sutton Bridge Crop Storage Research, specially Dr Glyn Harper, for performing field and storage trials respectively, and Professor Paul Knox (Centre for Plant Sciences, University of Leeds) for kindly providing monoclonal antibodies. Dr Nik Watson for assistance with the high speed vii camera. I thank very much my colleagues and staff of the Food Science and Nutrition School who were present beside me during this experience. I would like to thank my husband Junior Roberti for his love and unequivocal support throughout, as always, for which my mere expression of thanks likewise does not suffice. My son Pietro and my daughter Julia for being the inspiration of my days. To my family, especially my parents Rogério and Lucia and my brother Luciano, for their personal support and great patience at all times. To the Bridge Street Church family, for their love, prayers and caring. Finally, my thanks go to all the people who have supported me to complete the research work directly or indirectly. viii Abstract Bruising of potato tubers leads to losses of 20% of the UK annual crop. The relationship between bruising, tuber physical and mechanical properties, and composition of phenolic acids, tyrosine and cell wall monosaccharides was explored in this thesis. Three field trials were undertaken and the varieties Lady Rosetta (LR), Maris Piper (MP) and Russet Burbank (RB) were grown in replicate field plots. Field trial 1 was designed to investigate the effect of harvest time and defoliation; field trial 2 was designed to investigate the effect of harvest and storage time and a third field trial was undertaken to investigate the effect of nitrogen application to soil (in variety LR only). Bruising was induced using a falling bolt for severe bruising and bruising index assessment. Weight, specific gravity and oxidative potential were also measured. Cortex and skin mechanical properties were measured using a TA.XT2i Texture Analyser. Phenolic acids, tyrosine and cell wall monosaccharides were analysed chemically using HPLC. The results from the field trials showed that tubers harvested ~ 150 days after planting varied in susceptibility to bruising for MP (11-60%), LR (14- 52%) and RB (50-92%). Earlier harvest (98-139 days) showed lower incidence of bruising for MP (0-16.7%) and LR (17-23%) but not always for RB (0-66.7%). Late harvest (180 days) presented high incidence of bruising for all varieties varying from 81-88%. Short storage periods (until January) did not increase bruising significantly. Long storage periods (March) increased incidence of bruising for all ix varieties, and is associated with higher specific gravity, higher tissue deformability and higher phenolic acid and tyrosine levels. Potato plants defoliated 49 days before harvest showed lower bruising incidence than undefoliated samples, but had significantly (p<0.05) lower weight. Application of nitrogen increased weight of tubers and was associated with higher bruising incidence of LR when tubers were harvested later than 92 days after planting. Tyrosine levels or specific gravity were not always associated with highest bruising incidence. Hot dry conditions during tuber development (observed in field trial 2) was associated with early plant senescence and high tuber bruising incidence. In conclusion, bruising is affected by agricultural and post-harvest practices, and is determined by a number of physical and biochemical factors that vary between variety. The factors determining bruising seem to be dependent upon variety and the maturity of the tubers at harvest. Understanding these factors will help growers manage their crop to optimize quality and minimize waste. x Table of Contents 1 INTRODUCTION ...........................................................................................................32 1.1 Origin and physiology ................................................................................................32 1.2 Importance of potato in world economy ...................................................................32 1.3 Quality of potato ..........................................................................................................35 1.4 Bruising ........................................................................................................................36 1.4.1 Bruising assessment ............................................................................................38 1.5 Factors influencing bruising in potatoes .................................................................42 1.5.1 Genotypic characteristics .....................................................................................42 1.5.2 Phenolic acids ......................................................................................................43 1.5.3 Tyrosine ................................................................................................................49 1.5.4 Cell walls ..............................................................................................................52