Angelika Krumbein

Sensory analysis, sugar and acid content of tomato at different EC values of the nutrient solution

The influence of three concentrations of nutrient solution (electrical conductivity, EC: 1.0, 3.5 and 6.0 dS m ˇ1 ) on the sensory properties of tomato was investigated. Two tomato cultivars representing two types—a conventional round tomato (cv. Counter) and a round longlife tomato (cv. Vanessa)—were harvested from a closed hydroponic system with recirculating nutrient solution. The same products were investigated by quantitative descriptive analysis with trained panellists and by an acceptance test with consumers. Furthermore, the contents of reducing sugars and the titratable acid of fruits were analysed. To find explanations for consumer preferences relationships between the results of quantitative descriptive analysis, consumer acceptance tests and the sugar and acid contents of the fruits were investigated. The quantitative descriptive analysis revealed changing intensities of sensory attributes of appearance, firmness by touch, flavour, aftertaste and mouthfeel with increasing nutrient solution EC. However, the change of different sensory attributes was different for the two cultivars. Intensity of unfavourable flavour attributes such as mouldy, spoiled sweetish and bitter was stronger only for the longlife cultivar when cultivated at high EC. Higher EC values resulted in higher contents of reducing sugars and titratable acid, which influenced the intensity of several sensory attributes of smell, flavour and aftertaste evaluated by the descriptive panel. Scientia Horticulturae 82 (1999) 227‐242

UV-B-Induced Secondary Plant Metabolites - Potential Benefits for Plant and Human Health

Epidemiological studies have revealed an inverse association between the consumption of fruit, vegetables, and herbs and the risk of both cancer and cardiovascular disease. This protective effect is mostly due to secondary metabolites present in plant tissues. During the last decade, it has become increasingly clear that UV-B radiation is an important regulator of plant secondary metabolism. Low, ecologically-relevant UV-B levels trigger distinct changes in the accumulation of, among others, phenolic compounds, carotenoids and glucosinolates. Fundamental understanding of plant UV-B perception and responses opens up new opportunities for crop manipulation. Thus, targeted low dosage UV-B radiation treatments as emerging technology may be used to generate fruit, vegetables, and herbs enriched with secondary plant metabolites for either fresh consumption or as a source for functional foods and nutraceuticals, resulting in increased ingestion of these health-promoting substances. The UV-B induced accumulation of secondary plant metabolites is likely to have evolved as a plant defense response against harmful UV-B radiation. However, UV-B induced secondary metabolites also alter other trophic interactions, for example by altering plant herbivore resistance. Thus, UV-B driven metabolic changes in the plants secondary metabolism have benefits for both ends of the bio-based food chain, i.e., for plants themselves as well as for humans.

UV-B irradiation changes specifically the secondary metabolite profile in broccoli sprouts: induced signaling overlaps with defense response to biotic stressors.

Only a few environmental factors have such a pronounced effect on plant growth and development as ultraviolet light (UV). Concerns have arisen due to increased UV-B radiation reaching the Earth’s surface as a result of stratospheric ozone depletion. Ecologically relevant low to moderate UV-B doses (0.3–1 kJ m–2 d–1) were applied to sprouts of the important vegetable crop Brassica oleracea var. italica (broccoli), and eco-physiological responses such as accumulation of non-volatile secondary metabolites were related to transcriptional responses with Agilent One-Color Gene Expression Microarray analysis using the 2×204 k format Brassica microarray. UV-B radiation effects have usually been linked to increases in phenolic compounds. As expected, the flavonoids kaempferol and quercetin accumulated in broccoli sprouts (the aerial part of the seedlings) 24 h after UV-B treatment. A new finding is the specific UV-B-mediated induction of glucosinolates (GS), especially of 4-methylsulfinylbutyl GS and 4-methoxy-indol-3-ylmethyl GS, while carotenoids and Chl levels remained unaffected. Accumulation of defensive GS metabolites was accompanied by increased expression of genes associated with salicylate and jasmonic acid signaling defense pathways and up-regulation of genes responsive to fungal and bacterial pathogens. Concomitantly, plant pre-exposure to moderate UV-B doses had negative effects on the performance of the caterpillar Pieris brassicae (L.) and on the population growth of the aphid Myzus persicae (Sulzer). Moreover, insect-specific induction of GS in broccoli sprouts was affected by UV-B pre-treatment.

Sensory analysis and instrumental measurements of short-term stored tomatoes (Lycopersicon esculentum Mill.)

Abstract The effect of short-term storage of tomatoes (air temperature 20°C, relative air humidity 55%, air velocity

Identification of complex, naturally occurring flavonoid glycosides in kale (Brassica oleracea var. sabellica) by high‐performance liquid chromatography diode‐array detection/electrospray ionization multi‐stage mass spectrometry

Kale is a member of the Brassicaceae family and has a complex profile of flavonoid glycosides. Therefore, kale is a suitable matrix to discuss in a comprehensive study the different fragmentation patterns of flavonoid glycosides. The wide variety of glycosylation and acylation patterns determines the health-promoting effects of these glycosides. The aim of this study is to investigate the naturally occurring flavonoids in kale. A total of 71 flavonoid glycosides of quercetin, kaempferol and isorhamnetin were identified using a high-performance liquid chromatography diode-array detection/electrospray ionization multi-stage mass spectrometry (HPLC-DAD/ESI-MS(n)) method. Of these 71 flavonol glycosides, 27 were non-acylated, 30 were monoacylated and 14 were diacylated. Non-acylated flavonol glycosides were present as mono-, di-, tri- and tetraglycosides. This is the first time that the occurrence of four different fragmentation patterns of non-acylated flavonol triglycosides has been reported in one matrix simultaneously. In addition, 44 flavonol glycosides were acylated with p-coumaric, caffeic, ferulic, hydroxyferulic or sinapic acid. While monoacylated glycosides existed as di-, tri- and tetraglycosides, diacylated glycosides occurred as tetra- and pentaglycosides. To the best of our knowledge, 28 compounds in kale are reported here for the first time. These include three acylated isorhamnetin glycosides (isorhamnetin-3-O-sinapoyl-sophoroside-7-O-D-glucoside, isorhamnetin-3-O-feruloyl-sophoroside-7-O-diglucoside and isorhamnetin-3-O-disinapoyl-triglucoside-7-O-diglucoside) and seven non-acylated isorhamnetin glycosides.

Effect of different water supply on plant growth and fruit quality of Lycopersicon esculentum

It is well known from earlier work that water stress and salinity results in depressed plant growth and high fruit quality of tomato (e.g. increased sugar and acid levels), but generally is associated with a low marketable fruit yield. In the present work we investigated whether even a small reduction in water supply (without visible symptoms of water stress) also results in a high fruit quality together with high marketable fruit proportions. To characterize fruit quality sugars (glucose and fructose), titratable acids, odour-active aroma volatiles and vitamin C were investigated. Tomato plants (Lycopersicon esculentum Mill. cv Vanessa) were grown in soil and with the onset of fruit development water supply was varied (70% and 50% water capacity). In the treatment with lower water supply plant growth, and in particular the number of fruit settings were depressed and the sugar and vitamin C concentrations in the fruits were significantly increased, especially during fruit ripening. Furthermore, with lower water supply the concentrations of titratable acids and of C6 aldehydes (hexanal, (Z)-3-hexenal and (E)-2-hexenal) were significantly increased in the red fruits. Fruit growth was identical in both treatments. The higher levels of sugars, titratable acids, aroma volatiles and vitamin C are responsible for the higher fruit quality under conditions of lower water supply. Since not all fruits of the well watered plants became mature, the marketable yield in both treatments was rather similar and hence, together with a higher fruit quality in the treatment with lower water supply, high proportions of marketable fruits can be harvested. Einflus einer unterschiedlichen Wasserversorgung auf das Pflanzenwachstum und die Fruchtqualitat von Lycopersicon esculentum Es ist durch andere Arbeiten bekannt, dass Wasserstress und Salinitat zu einem gehemmten Pflanzenwachstum und hoher Fruchtqualitat bei Tomaten (z. B. erhohten Zucker- und Saurengehalten) fuhren; allerdings ist der marktfahige Fruchtertrag im allgemeinen reduziert. In der vorliegenden Arbeit wurde untersucht, ob bereits eine geringfugige Einschrankung der Wasserzufuhr (ohne sichtbare Symptome von Wasserstress) ebenfalls zu einer hohen Fruchtqualitat bei gleichzeitig hohem marktfahigen Fruchtertrag fuhrt. Zur Charakterisierung der Fruchtqualitat wurden Zucker (Glukose und Fruktose), titrierbare Sauren, fluchtige Aromastoffe und Vitamin C untersucht. Tomatenpflanzen (Lycopersicon esculentum Mill. cv Vanessa) wurden im Boden mit Beginn der Fruchtentwicklung bei optimaler und eingeschrankter Wasserversorgung (70% und 50% Wasserkapazitat) angezogen. Bei geringerer Wasserversorgung war das Pflanzenwachstum und insbesondere die Zahl der Fruchtstande erniedrigt und die Konzentrationen an Zuckern wie auch an Vitamin C in den Fruchten waren signifikant erhoht, und zwar insbesondere zur Reife. Daruberhinaus war bei reduzierter Wasserzufuhr in den reifen Fruchten die Konzentration der titrierbaren Sauren und der C6-Aldehyde (Hexanal, (Z)-3-Hexenal und (E)-2-Hexenal) signifikant erhoht. Das Fruchtwachstum war durch die unterschiedliche Wasserzufuhr nicht beeinflusst. Die hoheren Konzentrationen an Zuckern, titrierbaren Sauren, an fluchtigen Aromastoffen und an Vitamin C sind fur die hohere Fruchtqualitat bei geringerer Wasserversorgung verantwortlich. Da nicht alle Fruchte in der gut gewasserten Variante zur Ausreife gelangten, war der marktfahige Ertrag bei beiden Wasserstufen praktisch identisch, so dass also in der weniger gewasserten Variante qualitativ hoherwertige Fruchte ohne Ertragsdepression geerntet werden konnten.

Ontogenetic changes of 2-propenyl and 3-indolylmethyl glucosinolates in Brassica carinata leaves as affected by water supply.

Concentrations of 2-propenyl and 3-indolylmethyl glucosinolates in two lines of Brassica carinata (Holeta-1 and 37-A) were assessed during the vegetative life cycle under optimal or drought-inducing water supply conditions. In the well-watered treatment, 2-propenyl and 3-indolylmethyl glucosinolate concentrations remained almost constant from the 6-8 to the 15-16 leaf stage, whereas a drought-induced water supply led to a distinct increase of these glucosinolates. Generally, the 2-propenyl concentration was higher in Holeta-1 at each leaf stage under drought stress as compared with 37-A, indicating a B. carinata line-specific drought response. The drought-induced glucosinolate accumulation seems to be integrated in the plants process of osmotic adjustment. It seems that under drought, there is a shift from primary to secondary metabolism, thereby promoting glucosinolate synthesis. Thus, by keeping the relative soil-water content below 80%, glucosinolate concentrations could be increased up to the 15-16 leaf stage, resulting in better plant nutritional quality of B. carinata.

Genotypic and climatic influence on the antioxidant activity of flavonoids in kale (Brassica oleracea var. sabellica).

The influence of genotype and climatic factors, e.g. mean temperature and mean global radiation level, on the antioxidant activity of kale was investigated. Therefore, eight kale cultivars, hybrid and traditional, old cultivars, were grown in a field experiment and harvested at four different times. In addition to the investigation of the total phenolic content, the overall antioxidant activity was determined by TEAC assay and electron spin resonance spectrometry. A special aim was to characterize the contribution of single flavonoids to the overall antioxidant activity using an HPLC-online TEAC approach. The antioxidant activity and the total phenolic content were influenced by the genotype and the eco-physiological factors. The HPLC-online TEAC results showed that not all flavonol glycosides contribute to the overall antioxidant activity in the same manner. Taking the results of the structural analysis obtained by HPLC-ESI-MS(n) into account, distinct structure-antioxidant relationships have been observed.

Enhanced Glucosinolates in Root Exudates of Brassica rapa ssp. rapa Mediated by Salicylic Acid and Methyl Jasmonate

Elicitation studies with salicylic acid (SA) and methyl jasmonate (MJ) inducing a targeted rhizosecretion of high levels of anticarcinogenic glucosinolates in Brassica rapa ssp. rapa plants were conducted. Elicitor applications not only led to an accumulation of individual indole glucosinolates and the aromatic 2-phenylethyl glucosinolate in the turnip organs but also in turnip root exudates. This indicates an extended systemic response, which comprises the phyllosphere with all aboveground plant organs and the rhizosphere including the belowground root system and also root exudates. Both elicitor applications induced a doubling in 2-phenylethyl glucosinolate in root exudates, whereas application of MJ enhanced rhizosecreted indole glucosinolates up to 4-fold. In addition, the time course study revealed that maximal elicitation was observed on the 10th day of SA and MJ treatment. This study may provide an essential contribution using these glucosinolates as bioactive additives in functional foods and nutraceuticals.

Structurally different flavonol glycosides and hydroxycinnamic acid derivatives respond differently to moderate UV-B radiation exposure

The aim of this study was to investigate the modifying influence of moderate ultraviolet-B (UV-B) radiation exposure on structurally different flavonol glycosides and hydroxycinnamic acid derivatives during pre-harvest using kale, a leafy Brassica species with a wide spectrum of different non-acylated and acylated flavonol glycosides. Juvenile kale plants were treated with short-term (1 day), moderate UV-B radiation [0.22-0.88 kJ m⁻² day⁻¹ biologically effective UV-B (UV-B(BE))]. Twenty compounds were quantified, revealing a structure-specific response of flavonol glycosides and hydroxycinnamic acid derivatives to UV-B radiation. A dose- and structure-dependent response of the investigated phenolic compounds to additional UV-B radiation was found. The investigated quercetin glycosides decreased under UV-B; for kaempferol glycosides, however, the amount of sugar moieties and the flavonol glycoside hydoxycinnamic acid residue influenced the response to UV-B. Monoacylated kaempferol tetraglucosides decreased in the investigated UV-B range, whereas the monoacylated kaempferol diglucosides increased strongly with doses of 0.88 kJ m⁻² day⁻¹ UV-B(BE) . The UV-B-induced increase in monoacylated kaempferol triglucosides was dependent on the acylation pattern. Furthermore, the hydroxycinnamic acid glycosides disinapoyl-gentiobiose and sinapoyl-feruloyl-gentiobiose were enhanced in a dose-dependent manner under UV-B. While UV-B radiation treatments often focus on flavonol aglycones or total flavonols, our investigations were extended to structurally different non-acylated and acylated glycosides of quercetin and kaempferol.