Institute of Crop Science (340) Department of Agronomy Prof. Dr. Simone Graeff-Hoenninger Yacon (Smallanthus sonchifolius Poepp. & Endl) - the potential of a neglected crop as an alternative sweetener and source of phytochemicals for functional foods Dissertation submitted in fulfillment of the regulations to acquire the degree “Doktor der Agrarwissenschaften” (Dr.sc.agr. in Agricultural Sciences) to the Faculty of Agricultural Sciences by Forough Khajehei Born in Shiraz, Iran Stuttgart-Hohenheim September 2019 This thesis was accepted as a doctoral thesis (Dissertation) in fulfillment of the regulations to acquire the doctoral degree "Doktor der Agrarwissenschaften by the Faculty of Agricultural Sciences at University of Hohenheim on April 18, 2019. Date of the oral examination: June 6, 2019 Examination Committee Chairperson of the oral examination: Prof. Dr.-Ing. Stefan Boettinger Supervisor and Reviewer: Prof. Dr. Simone Graeff-Hoenninger Co-Reviewer: Prof. Dr.-Ing. Reinhard Kohlus Additional examiner: Prof. Dr. Torsten Mueller List of content Table of Contents List of abbreviations and acronyms ....................................................................................................... III List of figures ........................................................................................................................................ IV List of tables .......................................................................................................................................... IV 1. Introduction ..................................................................................................................................... 1 1. 1. Functional and health promoting plant based food products ................................................... 1 1. 2. General Outline and aims ........................................................................................................ 3 1. 3. Hypothesis ............................................................................................................................... 4 1. 4. Outline and structure of the thesis ........................................................................................... 6 2. Literature review ............................................................................................................................. 8 2. 1. Origin of yacon (Smallanthus sonchifolius Poepp. & Endl.) .................................................. 8 2. 2. Botanical and morphological characteristics of yacon (Smallanthus sonchifolius Poepp. & Endl.) 9 2. 3. Phyto/chemical characteristics of yacon leaves and tubers ................................................... 10 2. 4. Phyto/chemical characteristics of yacon leaves and tubers under the influence of genotype and environmental conditions ........................................................................................................... 12 2. 5. Phyto/chemical characteristics of yacon leaves and tubers under the influence of post-harvest handling and food processing conditions .......................................................................................... 13 2. 5. 1. Extraction processes of yacon leaves ............................................................................ 14 2. 5. 2. Drying of yacon tubers .................................................................................................. 15 3. Publications ................................................................................................................................... 17 4. Chapter I: Impact of Ohmic-Assisted Decoction on Bioactive Components Extracted from Yacon (Smallanthus sonchifolius Poepp.) Leaves: Comparison with Conventional Decoction ...................... 18 5. Chapter II: Yacon (Smallanthus sonchifolius Poepp. & Endl.) as a Novel Source of Health Promoting Compounds: Antioxidant Activity, Phytochemicals and Sugar Content in Flesh, Peel, and Whole Tubers of Seven Cultivars.......................................................................................................... 34 6. Chapter III: Total Phenolic Content and Antioxidant Activity of yacon (Smallanthus sonchifolius Poepp. and Endl.) Chips: Effect of Cultivar, Pre-Treatment and Drying .............................................. 53 7. General discussion ......................................................................................................................... 72 7. 1. The potential of yacon leaves and tubers as functional and health promoting food .............. 72 7. 2. Local food chain for yacon and its products ......................................................................... 73 7. 3. The Phyto/chemical characteristics of yacon leaves and their extraction ............................. 74 7. 4. Phyto/chemical characteristics of yacon tubers ..................................................................... 76 7. 5. Phyto/chemical characteristics of yacon chips ...................................................................... 79 8. Summary ....................................................................................................................................... 82 9. Zusammenfassung ......................................................................................................................... 85 I List of content 10. References ..................................................................................................................................... 89 Acknowledgement ................................................................................................................................. 98 Curriculum vitae .................................................................................................................................. 100 II List of abbreviations and acronyms List of abbreviations and acronyms % Percent °S Degree South, latitude °C Degree centigrade μmol Micromole μg Microgram a.s.l. Above sea level ABTS 2,2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt CHAD Convective hot air drying cm Centimetre cv. Cultivar DE Decoction DM Dry matter DPPH 2,2-diphenyl-1-picrylhydrazyl e.g. For example EU European Union FD Freeze drying FOS Fructooligosaccharides FRAP Ferric reducing antioxidant power g Gram kg Kilogram m Meter mg Milligram OH-DE Ohmic-assissted decoction TFC Total flavonoid content TPC Total phenolic content US/USA United States of America III List of figures and tables List of figures Figure 1. Locations of yacon cultivation. ................................................................................................ 8 Figure 2. Botanical and morphological attributes of yacon. .................................................................... 9 List of tables Table 1. Categorizing yacon tubers according to the colour of their peel and flesh. ............................ 10 IV Introduction 1. Introduction 1. 1. Functional and health promoting plant based food products The growing attention towards health promoting and functional food products in various sectors of the food supply chain, from primary production in the agricultural sector to the consumption point at the tables of the consumers’ houses is a reflection of the combination of a number of factors. Firstly, it has been forewarned that the world population will grow to 9 billion by 2050, with implications that strategies need to be developed that assure global food security (Godfray et al., 2010). It has been noted that in order to feed the future population the agricultural production should grow 50 to 70% (Horlings & Marsden, 2011; Karunasagar & Karunasagar, 2016). However, population growth is not the only factor at play in regard to the upward trend for food demand. The continuously raising level of awareness of the link between health and diet has induced certain alterations in diet, consumers’ food choices and raw material demand (Ubeda et al., 2011). Some of the most significant characteristics of modern diets are the high intake of sugar, fat and protein which have been recognized among the contributing factors of specific chronic diseases such as obesity, type II diabetes, coronary heart disease, etc. More precisely, animal protein consumption, particularly meat consumption has been associated with the risk of chronic diseases such as colorectal cancer, cardiovascular diseases, and obesity (Hu, 2011; Godfray et al., 2018; Wang & Beydoun, 2009). Although, meat serves as a source of energy and certain nutrients (iron, zinc and vitamin B12), it is possible to provide most of these nutrients without meat through maintaining a wide variation of food products in the diet (Godfray et al., 2018). The rising pattern of meat consumption has a negative impact on environment and use of water and land. Moreover, studies have shown that plant based diets such as a lacto-ovo-vegetarian diet is a more sustainable diet in terms of usage of resources such as energy, land and water and is healthier as well (Heller & Keoleian, 2015; Ruini et al., 2015). Consequently, the demand for plant based food products is raising, which has led the primary production sector to focus on enhancing the production of crops such as e.g. quinoa, hemp, soy, legumes. These crops can contribute to maintaining plant based proteins and nutrients in the diet (Friedman, 1996; Iqbal, Khalil, Ateeq, & Khan, 2006; Tang, Ten, Wang, & Yang, 2006). Several studies have shown that the diet plays a crucial role in the occurrence of certain chronic diseases
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