Browsing by Subject "Smallanthus sonchifolius"

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    A cropping system for yacon (Smallanthus sonchifolius Poepp. Endl.) : optimizing tuber formation, yield and sugar composition under European conditions
    (2020) Kamp, Larissa; Graeff-Hönninger, Simone
    The demand of healthy food is constantly increasing in Germany, as well as in developed countries in general. Here "healthy" is not clearly defined but it is often associated with foods indicating a low caloric value and further health-promoting benefits such as a high proportions of dietary fiber, phenols or antioxidants. In contrast, the proportion of obese people and the number of chronic diseases such as diabetes type II and obesity are increasing. As a result, the European Commission recommended to reduce the sugar content and the caloric value of food products, especially in sweetened beverages, breakfast cereals and dairy products by 10%. In general, a distinction can be made between artificial and natural sweeteners. Natural sweeteners such as honey, agave nectar or rapadura occur naturally and do not have to be artificially produced or synthesized. Disadvantages here are the high production costs as well as the high calorie value which is similar to conventionally used sugar. Artificial sweeteners, on the other hand, which are also known as "high-intensity sweeteners", have been artificially produced or synthesized. Examples are aspartame, saccharin or sucralose. They often have a lower calorie value (except for sugar alcohols such as xylitol or sorbitol) and are more economical to produce, which makes them particularly attractive for food producers. However, artificial sweeteners are suspected of being harmful to health or even carcinogenic. As a result, the consumer acceptance of artificial sweeteners is decreasing and the demand for natural sweeteners as alternatives is increasing. A possible alternative as a natural sweetener is yacon (Smallanthus sonchifolius). Yacon is a tuberous root crop native to the Andean region. The roots store carbohydrates mainly as fructooligosaccharides (FOS). These FOS cannot be digested by the human intestinal tract, and therefore do not cause a noticeable increase of blood glucose level. In addition, high amounts of fiber, phenols and antioxidants lead to further health promoting benefits. So far, yacon has been cultivated mainly in the Andean region in smallholder structures. Therefore, there are several open questions regarding the cultivation of yacon in Europe, especially in the area of propagation, choice of genotypes and adapted nitrogen fertilization. Especially the propagation is an important factor, as it is normally done by seedlings of mother plants or single rhizome pieces, both with pre-cultivation in the greenhouse. This is expensive and leads to a price of 3.60 € for young plants. In addition, the influence of genotype and amount of nitrogen fertilization on tuber yield and sugar composition has not been investigated yet. These open questions regarding the cultivation of yacon in Europe outline the following objectives: • to evaluate differences between direct planting and pre cultivation of rhizomes in two ways with regard to yacon growth, development, tuber yield formation and cost distribution; • to investigate the yield potential of different yacon genotypes with regard to tuber yield, sugar yield and tuber composition under the given climatic conditions of Europe; • to determine the influence of different nitrogen levels on nitrogen uptake, tuber yield formation and amount of monosaccharides and polysaccharides as well as total sugar; • to investigate the environmental impact and the production costs of different yacon cultivation systems to determine the most sustainable cultivation method. To achieve the objectives, field trials were carried out a from 2016 to 2018. As a result, four scientific publications were developed, which formed the body of this thesis. Publication I focused on the differences between a propagation with pre-cultivation in the greenhouse (DSAB), rhizome pieces with pre-cultivation in the greenhouse (RP1) and a direct planting of rhizome pieces (RP2) in agronomic and economic terms. RP1 achieved the highest yield with 29.8 t ha 1 FM and differed significantly from the other treatments with 21.3 and 17.8 t ha-1 FM (DSAB and RP2, respectively). With regard to the cost per kg of produced yacon, RP1 was also convincing, which can be explained by a high tuber yield and comparatively low propagation costs. DSAB was the most expensive treatment and is therefore not recommended. Contrary to that RP2 has a high potential for mechanization and yield increases. Publication II investigated the differences between nine different genotypes with respect to tuber yield and sugar composition. The three genotypes red-shelled, brown-shelled and Morado achieved the significantly highest tuber yields with 46.6, 43.5 and 41.6 t FM ha-1. Also the sugar contents were outstanding with up to 66% of the DM in the red-shelled genotype. As a result, the sugar yields of these three genotypes were highest with 2.2, 2.0 and 1.9 t ha-1 in the same order as the tuber yields. In Publication III the influence of different amounts of nitrogen fertilizer (0, 40 and 80 kg ha-1) on tuber yield, sugar composition and nitrogen uptake of the brown- and red-shelled genotype was investigated. Both genotypes reached highest tuber yields of 50 and 67 t FM ha-1 at the highest nitrogen fertilizer amount (brown- and red-shelled, respectively). Contrary to this responded the total amounts of sugar and FOS. Both decreased with increasing amounts of nitrogen. With decreasing amounts of FOS, the proportion of FOS with higher degree of polymerization (DP) increased. With regard to the nitrogen utilization efficiency of both, tubers and the entire plant, a nitrogen amount of 40 kg N ha-1 seems to be sufficient and recommendable. Publication IV examined the ecological and economic sustainability of the cultivation of two genotypes (brown- and red-shelled), each with pre-cultivation in the greenhouse and as direct planting, with three different nitrogen fertilizer levels. The aim was to investigate the environmental impact and production costs of different yacon cultivation systems. Considering the costs, the highest fertilizer amount (80 kg N ha-1) led to the lowest production costs and also to comparatively low environmental impacts per functional unit (1 kg FOS). The red-shelled genotype performed better, both in terms of cost and environmental impact. This was mainly due to higher tuber yields. Overall, the preceding publications showed that the cultivation of yacon in Europe is possible and offers new possibilities for farmers. Embedding yacon successfully into existing cropping systems and crop rotations seems to be possible. The farmer has the opportunity to establish a promising new crop with great value potential on his farm in order to cover the increasing demand for raw materials for natural sweeteners.
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    Yacon (Smallanthus sonchifolius Poepp. & Endl) - the potential of a neglected crop as an alternative sweetener and source of phytochemicals for functional foods
    (2019) Khajehei, Forough; Graeff-Hönninger, Simone
    Yacon (Smallanthus sonchifolius Poepp. & Endl.) as an underutilized crop, native to the Andean region, has attracted growing attention. The tuberous roots of yacon have been advertised as an alternative low caloric plant source for replacing sucrose. In fact, yacon has gained recognition based on the fact that its sweet tasting tuberous roots and its leaves have a favourable phytochemical content to be included in a range of functional food products. The leaves on the one hand are a significant source of health promoting phenolic compounds and their extract exerts certain biological activities such as antioxidant activity and hyperglycemic effects. The tubers on the other hand consist of carbohydrates including simple sugars, namely, fructose, glucose, sucrose and fructooligosaccharides (FOS). The FOS - representing the dominant polysaccharide in the tubers - are sweet tasting, prebiotic, and non-digestible oligosaccharides. Therefore, their consumption imposes several health benefits such as lowering the energy intake while enhancing the beneficial microflora of the colon. It is noted that 60-70 % of the dry matter content of yacon tubers is composed of FOS. Besides, yacon tubers are a remarkable source of biological components such as phenolic compounds. Thus, yacon is considered as multifunctional plant food. The main objectives of this thesis were to 1) differentiate between the quality of young and old yacon leaves of two cultivars (red and white) in terms of their total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity when using ohmic-assisted decoction (OH-DE) and decoction (DE) as well as energy consumption of extraction process, 2) differentiate between various parts of yacon tubers (flesh, peel and whole tuber) of seven cultivars in terms of their simple sugar (fructose, glucose and sucrose) content, TPC, TFC and antioxidant activity, 3) examine the TPC and antioxidant activity of yacon tubers of two cultivars (red and white) one week and three weeks after the harvest and under the influence of different pre-treatments before drying, and 4) determine the effect of drying on quality of yacon chips produced from two cultivars (red and white) at two time intervals after harvest. Overall, this thesis provided a broad dataset und information with regard to phytochemical contents of yacon leaves and tubers of different cultivars grown under the environmental conditions of southwestern Germany. However, further studies with regard to the determination of individual functional constitutes of leaves and tubers of yacon, their mechanism of action and effectiveness in promoting the health benefits, and their safety is essential. Moreover, with regard to novel product development from yacon leaves and tubers, further studies are strongly suggested to ensure the sustainability of final food products by optimizing energy consumption and environmental impacts of the whole food supply chain for such products as well as their quality.