Nikolaus Merkt

Screening of industrial wastewaters as feedstock for the microbial production of oils for biodiesel production and high-quality pigments

The production of biodiesel has notably increased over the past decade. Currently, plant oil is the main feedstock for biodiesel production, but, due to concerns related to the competition with food production, alternative oil feedstocks have to be found. Oleaginous yeasts are known to produce high amounts of lipids, but no integrated process from microbial fermentation to final biodiesel production has reached commercial realization yet due to economic constraints. Therefore, growth and lipid production of red yeast Rhodotorula glutinis was tested on low-cost substrates, namely, wastewaters from potato, fruit juice, and lettuce processing. Additionally, the production of carotenoids as high-value by-products was examined. All evaluated wastewaters met the general criteria for microbial lipid production. However, no significant increase in lipid content was observed, probably due to lack of available carbon in wastewaters from fruit juice and lettuce processing, and excess of available nitrogen in potato processing wastewater, respectively. During growth on wastewaters from fruit juice and lettuce processing the carotenoid content increased significantly in the first 48 hours. The relations between carbon content, nitrogen content, and carotenoid production need to be further assessed. For economic viability, lipid and carotenoid production needs to be increased significantly. The screening of feedstocks should be extended to other wastewaters.

Characterization of different biomasses based on their sugar profile with focus on their utilization for microbial biodiesel production.

The investigation and characterization of different biomasses as potential feedstocks for microbial lipid production was the aim of the present work. Twenty-eight biomasses were analyzed for total sugar content (glucose and xylose) and C/N-ratio as two major criteria for a suitable lipid production by oleaginous microorganisms. Considering both parameters, 9 out of 28 biomasses seemed to be suitable feedstocks for microbial lipid production. To allow for a broad evaluation of the suitability of the potential feedstocks, the estimated sugar and potential energy yield per area were calculated and the production costs and energy demand of the feedstock production were considered.

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

The aim of this study was to evaluate the quality characteristics of seven yacon (Smallanthus sonchifolius Poepp. and Endl.) cultivars (Cajamarca, Cusco, Early White, Late Red, Morado, New Zealand and Quinault) cultivated in the southwest of Germany. The following phyto/chemical traits were investigated in different yacon tuber parts (flesh, peel, and whole tubers): total dry matter, sugar content (fructose, glucose, and sucrose content), total phenolic content (TPC), total flavonoid content (TFC), 2,20-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, and Ferric reducing antioxidant power (FRAP). The results indicated a significant interaction between cultivar and tuber part on all of the examined traits (p < 0.0001). Of flesh and whole tuber, cv. Late Red, cv. Morado, and cv. Cajamarca had the highest TPC, TFC, DPPH radical scavenging activity, and FRAP. They also had relatively higher total sugar content. Cv. New Zealand had the lowest amount of sugars, TPC, TFC, DPPH radical scavenging activity, and FRAP, but the highest ABTS radical scavenging activity content in its flesh and whole tuber. Moreover, the results indicated that the peel of yacon tubers contained considerably high amounts of phytochemicals while possessing low sugar contents. Overall, this study provides a broad insight into the phyto/chemical content of yacon tubers from different cultivars, which can be used for further breeding programs, and the selection of proper cultivars for specific food product development.

Anthocyanin management in fruits by fertilization

Anthocyanins are water-soluble vacuolar plant pigments that are mainly synthesized in epidermal layers and the flesh of fruits such as apples, cherries, grapes, and other berries. Because of their attractive red to purple coloration and their health-promoting potential, anthocyanins are significant determinants for the quality and market value of fruits and fruit-derived products. In crops, anthocyanin accumulation in leaves can be caused by nutrient deficiency which is usually ascribed to insufficient nitrogen or phosphorus fertilization. However, it is a little-known fact that the plants nutrient status also impacts anthocyanin synthesis in fruits. Hence, strategic nutrient supply can be a powerful tool to modify the anthocyanin content and consequently the quality and market value of important agricultural commodities. Here we summarize the current knowledge of the influence of plant nutrients on anthocyanin synthesis in fruits of major global market value and discuss the underlying cellular processes that integrate nutrient signaling with fruit anthocyanin formation. It is highlighted that fertilization that is finely tuned in amount and timing has the potential to positively influence the fruit quality by regulating anthocyanin levels. We outline new approaches to enrich plant based foods with health-promoting anthocyanins.

Impact of Ohmic-Assisted Decoction on Bioactive Components Extracted from Yacon (Smallanthus sonchifolius Poepp.) Leaves: Comparison with Conventional Decoction

Yacon (Smallanthus sonchifolius Poepp.) leaves are a potentially rich source of bioactive compounds, such as phenolic acids and flavonoids. In this study, the effect of the extraction method (ohmic-assisted decoction (OH-DE) and decoction (DE)), yacon cultivar (red and white), and leaf age (young and old) on the quality/quantity of extracted phytochemicals were investigated. Extraction yield, energy consumption, total phenolic content (TPC), total flavonoid content (TFC), ABTS and DPPH radical scavenging activity, and ferric reducing antioxidant power (FRAP) were determined. Additionally, HPLC-DAD was used to identify the major individual phenolic and flavonoid compounds of yacon leaves. The results showed that a three-way interaction of process-variables (extraction method×yacon cultivar×age of leaves) influenced the extraction yield, TPC, TFC, ABTS, and DPPH radical scavenging activity, and FRAP, significantly (p < 0.05). However, energy consumption of the extraction process was only affected by method of extraction (p < 0.05) and was halved when OH-DE was applied as compared to DE alone. Additionally, the phytochemical quality of extracts was either improved or comparable when OH-DE was used for extraction. Also, it was shown that yacon leaves contained considerable amounts of caffeic acid, chlorogenic acid, ferrulic acid, myricetin, p-coumaric acid, and rutin, while leaves of the red cultivar had higher contents of each compound compared to leaves of the white cultivar.

Different nitrogen (N) forms affect responses to N form and N supply of rootstocks and grafted grapevines

Rootstocks play an important role in the cultivation of grapevines. In addition to the uptake and storage of nutrients, rootstocks and their root system affect the growth and metabolite composition of the berries. Nitrogen can be taken up in various forms, such as nitrate, ammonium or amino acids or even small peptides, and is of considerable importance in vigor control and in yield and berry quality. Amino acids in the must adjust fermentation kinetics, constitute a major source for yeast and affect vine metabolism. In the present study, two different experiments were undertaken; nitrate, ammonium, urea, arginine and glutamine at various doses (0; 0.5; 1.0; 3.0 g N/plant) were used to fertilize (i) two hydroponically grown rootstock varieties (Ru140 and SO4) and (ii) grafted grapevines of Vitis vinifera L cv. Regent (rootstock SO4) grown in pots. Accumulation capabilities, generative growth and berry quality were examined. It can be assed that the preferred N form is rootstock-variety-dependent. We demonstrated that grapevines were able to take up nitrogen in the form of amino acids; (arginine to a greater extent than glutamine). Although, growth was reduced, nitrogen content and nitrate reductase activity were comparable for nitrate, ammonium and urea nutrition. In terms of berry quality, only minor differences between the N forms applied were identified. An economic optimum in terms of vine and berry quality was detected. Excessive amounts of nitrogen seemed to lead to the increased growth of green plant tissue. Berry yield increased with increasing nitrogen supply but slightly decreased at the highest dosage, whereas quality parameters such as must pH increased and the total acid concentration was reduced.

Impact of Nitrogen and Sulfur Supply on the Potential of Acrylamide Formation in Organically and Conventionally Winter Wheat

In a two-year field trial, the effect of nitrogen (N) and sulfur (S) fertilization was 11 investigated on grain yield, grain quality parameters, formation of acrylamide (AA), and the 12 precursor free asparagine (Asn) in organically and conventionally produced winter wheat cultivars. 13 In both production systems, different types, amounts, and temporal distributions of N were tested. 14 While the effect of S fertilizer types and amounts on free Asn was only tested in the conventional 15 farming system. 16 Within both cropping systems, grain yield and baking quality were significantly influenced by N 17 treatment while the effect on free Asn was only minor. Especially within the organic farming system, 18 increasing N fertilization levels did not increase free Asn significantly. A slight trend of increasing 19 free Asn levels with an intensified N supply was observed, especially in the presence of crude 20 protein contents of 14 % or higher. But only N amounts of 180 kg N ha-1 or higher increased the 21 probability of high free Asn contents considerably, while N supply below that amount led to free 22 Asn values similar to the unfertilized controls. The results indicated that good baking quality can 23 be achieved without significantly increasing free Asn levels. 24 In addition, cultivars affected the levels of free Asn significantly. Compared to cv. “Bussard” and 25 “Naturastar”, cv. “Capo” exhibited the lowest AA formation potential at an N supply of 180 kg N 26 ha-1 while simultaneously reaching a crude protein content > 15 % (conventional) and > 12 % 27 (organic). Thus, it seems that cultivars differ in their ability to store and incorporate free Asn into 28 proteins. 29 Over all trials, a correlation of free Asn and AA was shown by R2 = 0.77, while a relation of free Asn 30 and protein was only R2 = 0.36. Thus, lowering free Asn by adjusting N treatments should not 31 necessarily affect baking quality. 32 S nutrition within conventional farming did not change free Asn amount or crude protein 33 significantly, probably due to the fact that soil was not sulfate-deficient. 34 In summary, it was evident that free Asn amounts in wheat varied widely both within cultivars and 35 between cropping systems. In order to clearly unravel genotypic differences and their interaction 36 with environmental factors and especially N fertilization, further research is needed. 37

Acrylamide Formation Potential of Organically and Conventionally Grown Cereals

As bakery products contribute considerably to the daily intake of the carcinogen acting substance acrylamide (AA), the aim of this study was to evaluate the impact of the cropping system (conventional vs. organic farming) on AA precursor levels of free asparagine (Asn) across different cultivars of the cereal species, namely winter wheat (Triticum aestivum), winter spelt (Triticum aestivum ssp. spelta) and winter rye (Secale cereale) with simultaneous consideration of gained grain yields and flour qualities. For this purpose, orthogonal field trials were established at two sites in Southwest Germany over two growing seasons (2006-2007 and 2007-2008). The results indicated a significant impact of the cropping system on free Asn contents. Across all species, free Asn contents in the flour were 26 % lower under organic compared to conventional farming. The impact of the cropping system on individual cultivars was obvious with a maximum reduction in free Asn contents of 50 % (e.g. for cultivars Ludwig, Privileg, Capo) if organically produced. For spelt, a significant impact of the cropping system was only found in 2008 with a reduction in free Asn of up to 25 % if organically produced. Across both cropping systems, cultivar Franckenkorn reached the lowest levels of free Asn. For rye, a significant impact of the cropping system was observed only in 2007 with 33 % higher Asn amounts in the conventional cropping system. Independent of the cropping system, rye reached the highest levels of free Asn followed by wheat and spelt. Across both cropping systems, species and cultivars, the amount of free Asn correlated with the AA content in heated flour with R2=0.63***. Furthermore, the results indicated that lower AA contents in bakery products can be achieved by proper selection of species (e.g. 66 % lower if rye is replaced by wheat) and cultivars. With an appropriate choice of the cultivar, a reduction of up to 65 % was possible within wheat, along with a reduction of 44 % within spelt and 12.5 % within rye. In summary, the results indicated that organically produced wheat especially offers the opportunity to significantly lower the AA potential of bread and bread rolls by the choice of raw materials low in free Asn.

Quality aspects in open-pollinated onion varieties from Western Europe

Commercial onion breeders limit their selection criteria by focusing almost exclusively on conventional farming. This raises the demand for certain well known varieties, but lowers the general diversity available on the mainstream market. A way to maintain biodiversity is to preserve old open-pollinated varieties. Through their distinct aroma and flavor, these plants are again drawing the interest of farmers and consumers alike, making them a viable alternative to commercial varieties. To assess yield and quality aspects of West-European open-pollinated onions, we have evaluated nine varieties and compared them against two of their commercial, well-established counterparts. The study included onion production on the field in South-West Germany, evaluation of the quality and flavor parameters, as well as a trained sensory taste panel. Results showed high diversity in yield and chemical properties of the studied onion varieties, where two varieties in particular, stood out significantly. Compared to the control, the variety “Birnformige” performed best and demonstrated high concentrations of fructan and pyruvic acid, both known to have curative and medicinal properties. On the other end of the spectrum, the variety “Jaune des Cevennes” demonstrated low dry matter content, low concentration of enzymatically-produced pyruvic acid and a high bolting percentage. The study also confirmed the link between individual quality components in onion bulbs, including the significantly negative correlation between minerals (such as calcium and magnesium) and fructan.

Interaction between grapevines and trees: effects on water relations, nitrogen nutrition, and wine

ABSTRACT Agroforestry systems (AF) consisting of grapevines and trees, may lead to resource competition for water and nutrients. This study aimed to evaluate the impact of a combined cultivation on water relations, nitrogen nutrition and the resulting wine quality. 15N-labeled inorganic nitrogen (N) sources were used to quantify net N uptake capacity. N content and δ15N natural abundance were analysed as integrating parameters of N nutrition. Leaf water potential (ψleaf) was determined to evaluate the water status of grapevines. Wine quality was evaluated by chemical and sensory analyses. In result, AF system reduced leaf water potential and increased net N uptake capacity in grapevines. However, chemical composition and sensory quality of the wine were not significantly affected in the present system consisting of Riesling, Sauvignon Blanc, oak and poplar. Nitrogen availability of grapevines was favourable and water relations were improved, whereas wine quality was similar when grown with trees or without. Trees were able to reduce water and nitrogen losses without negative effects on wine quality. This work provides information on benefits and limits for intercropping of trees and grapevines in terms of performance of grapevines and wine quality compared to traditional vineyard systems.