Detlef Ulrich

QTL mapping of aroma compounds analysed by headspace solid-phase microextraction gas chromatography in the apple progeny ‘Discovery’ × ‘Prima’

Improving fruit quality of apple varieties is an important but complex breeding goal. Flavour is among the key factors of apple fruit quality but in spite of the analytical and biochemical knowledge about volatiles little is known about the genetic and molecular bases of apple aroma. The aim of this study was to use a saturated molecular linkage map of apple to identify QTLs for aroma compounds such as alcohols, esters and terpenes, but also for a number of unidentified volatile compounds (non-targeted analysis approach). Two parental genetic maps were constructed for the apple cultivars ‘Discovery’ and ‘Prima’ by using mainly AFLP and SSR markers. ‘Discovery’ and ‘Prima’ showed very different volatile patterns, and ‘Discovery’ mostly had the higher volatile concentrations in comparison with the Vf-scab resistant ‘Prima’ which has its origin in the small-fruited apple species Malus floribunda. About 50 putative QTLs for a total of 27 different apple fruit volatiles were detected through interval mapping by using genotypic data of 150 F1 individuals of the mapping population ‘C3’ together with phenotypic data obtained by head-space solid phase microextraction gas chromatography. QTLs for volatile compounds putatively involved in apple aroma were found on 12 out of the 17 apple chromosomes, but they were not evenly dispersed. QTLs were mainly clustered on linkage groups LG 2, 3 and 9. In a first attempt, a LOX (lipoxygenase) candidate gene, putatively involved in volatile metabolism, was mapped on LG 9, genetically associated with a cluster of QTLs for ester-type volatiles. Implications for aroma breeding in apple are discussed.

Diversity of aroma patterns in wild and cultivated Fragaria accessions

Plant breeders are interested in strawberry species as donors of volatile compounds in breeding programmes because of the diversity and intensity of wild strawberry aroma. Therefore, the topic of this paper is the prospective analysis of four accessions of four wild strawberry accessions in comparison to a standard cultivar of Fragaria × ananassa Duch. by using human sensory, gas chromatography mass spectrometry (GCMS) and gas chromatography–olfactometry (GCO). The wild species have higher aroma intensities compared with the cultivated one. The flavour quality differs significantly. Semiquantitative GC analysis revealed that F. × ananassa cv. ‘Elsanta’ has the lowest content of volatile compounds whereas Fragaria moschata L. ‘Cotta’ has the highest. The aroma impressions, measured by GCO, support the findings of GCMS analyses. The nasal impact frequency (NIF)-profiles of the wild types are more manifold and of higher intensities than those of the cultivated F. × ananassa cv. ‘Elsanta’ which corresponds with the overall flavour impression when tasting the fresh fruits.

Characterisation of ‘Galia’ melon aroma by GC and mass spectrometric sensor measurements after prolonged storage

Abstract The aroma development in two Israeli ‘Galia’ melon cultivars ( Cucumis melo var .reticulans , cv. C8 and cv. 5080), was monitored. Sensory assessment was also performed, along with measurements of firmness, colour, total soluble solids, and decay incidence. A new kind of mass spectrometric sensor measurement for aroma analysis was coupled with the headspace SPME-GC method. Generally, cv. C8 fruit had higher levels of aroma volatiles than cv. 5080 fruit, but a shorter shelf life. However, cv. 5080 fruit was firmer and had higher sugar contents and therefore, was more acceptable to consumers. In order to get the best quality, fruit should be harvested when light yellow with some green areas (colour 3). During maturity, 2-methylbutyl acetate, hexyl acetate, butyl acetate, 3-hexenyl acetate, and isobutyl acetate levels increased when the peel colour turned from green to light yellow. After applying multivariate statistics to the mass spectrometric sensor data obtained from the individual melon samples, separated factor groups were obtained from different postharvest examinations. A rapid and reliable prediction of the optimal harvest date is possible for both melon cultivars, based on the measured aroma profiles.

Identification of lipoxygenase (LOX) genes putatively involved in fruit flavour formation in apple (Malus × domestica)

Lipoxygenases (LOXs) are non-heme iron-containing enzymes that catalyse the dioxygenation of polyunsaturated fatty acids. The resulting hydroperoxides are further metabolized into biologically active oxylipins including jasmonic acid and green leaf volatiles (GLV) such as C6-aldehydes and C6-alcohols. LOXs are also known to play a decisive role in the production of volatiles that influence the flavour and aroma of fruits and vegetables. To obtain an overview of the inventory of the apple LOX gene family, the published Golden Delicious genome was mined for LOX coding sequences. In total, 23 putative functional LOX genes were identified and used for the construction of a phylogenetic tree. Two sub-trees were found which differentiate the LOX sequences into type 1- and type 2-LOXs. Their chromosomal locations were assigned to the predicted chromosomes of the assembled Golden Delicious genome sequence. Single LOX genes as well as clusters consisting of up to four genes were detected on apple chromosomes 2, 4, 5, 6, 7, 9, 11, 12, 13 and 16. LOX gene clusters on chromosomes 2 and 7, and on 4 and 12, respectively, indicated duplicated genome regions with high homology, which supports previous hypotheses of an ancient genome-wide duplication event in Malus. By using a PCR-based strategy, eight genes belonging to both type 1- and type 2-LOXs with altogether 30 full-length sequences were cloned. Several putative LOX alleles were detected within the same and among different apple cultivars. Two parental genetic maps available for ‘Discovery’ and ‘Prima’ were used for a quantitative trait locus (QTL) mapping experiment of apple volatile compounds known to be produced by the LOX biosynthetic pathway. The QTL detection resulted in a total number of 15 QTLs for eight volatiles (esters and the aldehyde hexanal) which were located on chromosomes 2, 7, 9 and 12 determined in silico as carriers of at least one LOX gene. To examine the putative roles of apple LOX genes in fruit volatile production, the spatial and temporal expression patterns were analysed by RT-PCR-based transcription analyses of apple leaf and fruit tissues. Two genes, MdLOX1a and MdLOX5e, were identified as candidate genes to be involved in fruit aroma volatile production in apple. The genetic association of QTLs found for the GLV hexanal at the top of chromosome 7, three clustered MdLOX5 genes with a putative 13-LOX function and published apple aphid resistance factors located all in the same region of chromosome 7 indicate that a lipoxygenase action might be involved in Malus aphid resistance reactions.

Diversity of volatile patterns in sixteen Fragaria vesca L. accessions in comparison to cultivars of Fragaria ×ananassa

Fragaria vesca is the most distributed wild species in the genus Fragaria . Due to this biogeography a high diversity is to expect. During two harvest seasons sixteen accessions from different locations from the most eastern habitat at Lake Baikal in Siberia, from Middle and Southern Europe and Northern Europe with Scandinavia and Iceland were investigated as well as two of the three described North American subspecies and three F. vesca cultivars. Five very distinct European F . ×ananassa cultivars were chosen to serve as a comparison. Beside brix value and acid contents the aroma patterns including 67 volatile compounds were quantified by stir bar sorptive extraction followed by gas chromatography with mass spectrometric detection. The diversity of important volatiles of Fragaria vesca and F . ×ananassa is discussed regarding biogeography, domestication, breeding and the so-called funnel effect.

Diversity of metabolite patterns and sensory characters in wild and cultivated strawberries 1

In breeding programs wild strawberry species are used increasingly to enhance the genetic diversity and to implement higher sensory quality. Next to Fragaria moschata L. and F. viridis Weston wild collections cultivars of Fragaria vesca L. were the standards for strawberry taste in Europe before the development of Fragaria × ananassa Duch. around 250 years ago. Therefore, the objective of this research was the evaluation of patterns of volatile organic compounds including around twenty strawberry character impact compounds evaluated for Fragaria vesca and in comparison for standard cultivars of Fragaria × ananassa. The metabolic patterns were measured using immersion-SBSE-GC-MS. Sixteen accessions of Fragaria vesca exhibit a high diversity in qualities and quantities of volatile organic compounds (VOCs). A specific fruit sampling strategy equalizes environmental caused variation and avoids misleading interpretations. The shown results are valuable for further breeding activities regarding flavor, transcriptomic analyses, studies of biochemical pathways and signaling compounds as well as marker development.

Chemometric tools for identification of volatile aroma-active compounds in oregano.

AbstractOne of the purposes of chemical analysis is to find quick and efficient methods to answer complex analytical questions in the life sciences. New analytical methods, in particular, produce a flood of data which are often very badly arranged. An effective way to overcome this problem is to apply chemometric methods. As part of the following investigations, three brands of oregano were analysed to identify their volatile aroma-active compounds. Two techniques were applied—gas chromatograpy–olfactometry (GC–O) and human sensory evaluation. Aroma-impact compounds could be identified in the main brands of oregano with the aid of chemometric methods (principal-components analysis, hierarchical cluster analysis, linear discriminant analysis, partial least-squares regression). Therefore, it is possible to reduce the analysis of sensory and olfactometry to relevant attributes. This makes classifying new species easier, much faster, and less expensive and is the premise for quick and more economic identification of new potential genotypes for oregano plant breeding. A comprehensive list of oregano key odourants, determined by GC–O and human sensory evaluation using different methods of supervised and unsupervised pattern cognition, has not previously been published. FigureOregano - a multi-faceted herb

A search for the ideal flavor of strawberry - Comparison of consumer acceptance and metabolite patterns in Fragaria × ananassa Duch.

in strawberry. Despite numerous investigations of the metabolic composition of strawberries, the description of the relationship between flavor pattern and consumer acceptance is inconsistent. The aim of the present study was to correlate overall liking (acceptance), the intensity of important sensory parameters, which were evaluated by a consumer panel, and data of instrumental analyses like soluble solids content, titratable acidity and volatile organic compound patterning. The data were collected over a period of three harvest years. They are suitable to reveal the relationships and interactions between the metabolite patterns of strawberry and the sensory properties due to the use of a high diversity of the gene pool and due to a special sample preparation with representative sample sizes for both human sensory and instrumental analysis. A high genetic diversity was considered including genotypes from cultivar crossing and from wild species introgression. It was found that the volatile compounds methyl 2-methylbutanoate, (Z)-3-hexenyl acetate, linalool and decanoic acid correlate positively with the attribute ‘sweet’ and, therefore, can act as sweetness enhancers. Furthermore, compounds were identified with positive (linalool, lactones) and negative impact (some esters, furanones) on the sensory quality. From these findings, strategies towards improved, sensorially valuable strawberry cultivars with a high consumer acceptance can be deduced. The online version of this article (doi: 10.5073/JABFQ.2016.089.029) contains supplementary files .

Sensory characteristics and volatile profiles of parsley ( Petroselinum crispum [Mill.] Nym.) in correlation to resistance properties against Septoria Blight ( Septoria petroselini ).

Sixteen different genotypes of parsley, including two cultivars, six populations, and eight inbred lines, were investigated regarding their sensory characteristics in relation to the volatile patterns and resistance to Septoria petroselini . The sensory quality was determined by a combination of profile analysis and preference test, whereas the volatile patterns were analyzed by headspace-SPME-GC of leaf homogenates with subsequent nontargeted data processing to prevent a possible overlooking of volatile compounds. The more resistant genotypes are characterized by several negative sensory characteristics such as bitter, grassy, herbaceous, pungent, chemical, and harsh. In contrast, the contents of some volatile compounds correlate highly and significantly either with resistance (e.g., hexanal and α-copaene) or with susceptibility (e.g., p-menthenol). Some of these compounds with very strong correlation to resistance are still unidentified and are presumed to act as resistance markers.

Influence of cultivar and harvest year on the volatile profiles of leaves and roots of carrots (Daucus carota spp. sativus Hoffm.).

The focus of the present work centers on the diversity of volatile patterns of carrots. In total 15 main volatiles were semiquantified in leaves and roots using isolation by headspace solid phase microextraction followed by gas chromatography with FID and MS detection. Significant differences in the main number of compounds were detected between the cultivars as well as the years. Genotype-environment interactions (G × E) are discussed. The most abundant metabolites, β-myrcene (leaves) and terpinolene (roots), differ in the sum of all interactions (cultivar × harvest year) by a factor of 22 and 62, respectively. A statistical test indicates significant metabolic differences between cultivars for nine volatiles in leaves and 10 in roots. In contrast to others the volatiles α-pinene, γ-terpinene, limonene, and myristicine in leaves as well as β-pinene, humulene, and bornyl acetate in roots are relatively stable over years. A correlation analysis shows no strict clustering regarding root color. While the biosynthesis in leaves and roots is independent between these two organs for nine of the 15 volatiles, a significant correlation of the myristicine content between leaves and roots was determined, which suggests the use of this compound as a bitter marker in carrot breeding.