Sensory Perception and Consumer Acceptance of Carrot Cultivars Are Influenced by Their Metabolic Profiles for Volatile and Non-Volatile Organic Compounds.

Sensory parameters as well as the volatile and non-volatile compound profiles of sixteen carrot cultivars were recorded to obtain insight into consumer preference decisions. The sensory test was carried out with a consumer panel of 88 untrained testers allowing a clear acceptance-based differentiation of the cultivars. Five individual sensory characters (sweetness, overall aroma, bitterness, astringency and off-flavor) supported this discrimination. Chemical analyses of volatile organic compounds, polyacetylenes, phenylpropanoids and sugars enabled us to correlate the influence of these ingredients on sensory perception. Higher concentrations of α-pinene, hexanal, styrene and acetophenone correlated with a better acceptance, as well as sweetness and overall aroma perception. In contrast, a low acceptance as well as a stronger perception of bitterness, astringency and off-flavor correlated with enhanced concentrations of camphene, bornylacetate, borneol, myristicine, falcarindiol, falcarindiol-3-acetate, laserin and epilaserin. The present study should support the development of new breeding strategies for carrot cultivars that better satisfy consumer demands.

Variation in Volatile Organic Compounds in native, synanthropic accessions and cultivars of the musk strawberry (Fragaria moschata Duchesne ex Weston).

Prior to the world-wide dominance of F. ×ananassa in strawberry production, native species had been cultivated in European gardens for centuries. Especially the musk strawberry (F. moschata) had been highly appreciated due to its fruit size and extraordinary aroma. Detailed studies on the diversity of the species' fruit aroma are lacking, although breeding aims to improve strawberry aroma by complex crossings during recent years. Today a few cultivars, abandoned synanthropic occurrences and native populations of this species exist in Germany. Here we characterised aroma profiles of F. moschata accessions by analysing Volatile Organic Compounds. In particular, differences between native and cultivated accessions as well as the diversity in aroma profiles of native populations were investigated. Profiles of Volatile Organic Compounds were analysed by immersion stir bar sorptive extraction-gas chromatography-quadrupol mass spectrometry (imm-SBSE-GC-qMS). These data were compared with a genetic characterisation of samples based on eight microsatellite loci using univariate and multivariate statistical analyses. High amounts of furanones and the key compound methyl anthranilate were characteristic for the aroma profile of F. moschata. We detected a considerable diversity of Volatile Organic Compounds among accessions of F. moschata, particularly among genetically distinct samples from the same population. Native accessions contained more terpenoids but less esters and were moderately differentiated from cultivated samples. The observed patterns of Volatile Organic Compounds indicate that cultivated accessions had been selected for favourable aroma profiles and thus showing traces of domestication. Moreover, native populations harbour a great diversity of Volatile Organic Compounds, which could be also considered for future breeding efforts.

Flavor and Other Quality Traits of Tomato Cultivars Bred for Diverse Production Systems as Revealed in Organic Low-Input Management.

This study was conducted to determine the volatile organic compounds (VOCs) associated with fruit flavor in diverse tomato cultivars (salad and cocktail cultivars) under organic low-input production. For this objective, 60 cultivars deriving from very diverse breeding programs 1880-2015 were evaluated in 2015, and a subset of 20 cultivars was selected for further evaluation in 2016. The diversity of instrumentally determined traits, especially for VOCs concentration and sensory properties (fruit firmness, juiciness, skin firmness, sweetness, sourness, aroma, and acceptability), was investigated at two harvest dates. The evaluation of the cultivars exhibited a wide range of variation for all studied traits, with the exception of a few VOCs. Cultivar had the most important effect on all instrumentally determined traits, while the influence of cultivar × harvest date × year interaction was significant for 17 VOCs, but not for total soluble solid (TSS) and titratable acidity (TA). The VOCs with the highest proportion (>8%) were hexanal, 6-methyl-5-heptene-2-one, 2-isobutylthiazole, and (E)-2-hexenal, which were identified in all cultivars. Twelve VOCs significantly correlated with one or more sensory attributes and these VOCs also allowed differentiation of the fruit type. Among these VOCs, phenylethyl alcohol and benzyl alcohol positively correlated with acceptability in the cocktail cultivars, whereas 2-isobuthylthiazole and 6-methyl-5-hepten-2-ol negatively correlated with acceptability in the salad cultivars. As a result of this study, organic breeders are recommended to use cultivars from a wide range of breeding programs to improve important quality and agronomic traits. As examples, salad tomatoes "Campari F1", "Green Zebra", and "Auriga", as well as cocktail tomatoes "Supersweet 100 F1", "Sakura F1", and "Black Cherry" showed higher scores for the sensory attributes aroma and acceptability under organic low-input growing conditions. It remains a challenge for breeders and growers to reduce the trade-off of yield and quality.

Influence of the Abiotic Stress Conditions, Waterlogging and Drought, on the Bitter Sensometabolome as Well as Agronomical Traits of Six Genotypes of Daucus carota.

Cultivated carrot is one of the most important vegetable plants in the world and favored by consumers for its typically sweet flavor. Unfortunately, the attractive sensory quality is hindered by a sporadic bitter off-taste. To evaluate the influence of the abiotic stress conditions, waterlogging and drought, on the bitter sensometabolome as well as agronomical traits of six genotypes of Daucus carota, a field trial was performed. Enabling the accurate tracing of carrots' bitter compounds and therefore their metabolic changes, a fast and robust high-throughput UHPLC-MS/MS was developed and validated. Remarkably, the genotypes are the driving source for the biological fate of the bitter metabolites that are reflected in concentrations, dose-over-threshold factors, and fold changes. A certain influence of the irrigation level is observable but is overruled by its cultivar. Therefore, metabolic stress response in carrots seems to be genotype dependent. Hence, this study might help to plant specific carrot genotypes that are adapted to stress conditions evoked by future climatic changes.

The carrot monoterpene synthase gene cluster on chromosome 4 harbours genes encoding flavour-associated sabinene synthases.

In plants, low molecular weight terpenes produced by terpene synthases (TPS) contribute to multiple ecologically and economically important traits. The present study investigates a carrot terpene synthase gene cluster on chromosome 4 associated with volatile monoterpene production. Two carrot mutants, yellow and cola, which are contrasting in the content of low molecular weight terpenes, were crossed to develop an F2 mapping population. The mapping analysis revealed overlapping QTLs on chromosome 4 for sabinene, α-thujene, α-terpinene, γ-terpinene, terpinen-4-ol and 4-carene. The genomic region of this locus includes a cluster of five terpene synthase genes (DcTPS04, DcTPS26, DcTPS27, DcTPS54 and DcTPS55). DcTPS04 and DcTPS54 displayed genotype- and tissue-specific variation in gene expression. Based on the QTL mapping results and the gene expression patterns, DcTPS04 and DcTPS54 were selected for functional characterization. In vitro enzyme assays showed that DcTPS54 is a single-product enzyme catalysing the formation of sabinene, whereas DcTPS04 is a multiple-product terpene synthase producing α-terpineol as a major product and four additional products including sabinene, ß-limonene, ß-pinene and myrcene. Furthermore, we developed a functional molecular marker that could discriminate carrot genotypes with different sabinene content in a set of 85 accessions.

A strawberry accession with elevated methyl anthranilate fruit concentration is naturally resistant to the pest fly Drosophila suzukii.

During the past decade, Drosophila suzukii has established itself as a global invasive fruit pest, enabled by its ability to lay eggs into fresh, ripening fruit. In a previous study, we investigated the impact of different strawberry accessions on the development of D. suzukii eggs, in the search of natural resistance. We identified several accessions that significantly reduced adult fly emergence from infested fruit. In the present study, we aimed at understanding the chemical basis of this effect. We first noted that one of the more resistant accessions showed an unusual enrichment of methyl anthranilate within its fruit, prompting us to investigate this fruit compound as a possible cause limiting fly development. We found that methyl anthranilate alone triggers embryo lethality in a concentration-dependent manner, unlike another comparable organic fruit compound. We also showed that a chemical fraction of the resistant strawberry accession that contains methyl anthranilate carries some activity toward the egg hatching rate. Surprisingly, in spite of the lethal effect of this compound to their eggs, adult females are not only attracted to methyl anthranilate at certain concentrations, but they also display a concentration-dependent preference to lay on substrates enriched in methyl anthranilate. This study demonstrates that methyl anthranilate is a potent agonist molecule against D. suzukii egg development. Its elevated concentration in a specific strawberry accession proven to reduce the fly development may explain, at least in part the fruit resistance. It further illustrates how a single, natural compound, non-toxic to humans could be exploited for biological control of a pest species.

What Do We Know about the Chemistry of Strawberry Aroma?

The strawberry, with its unique aroma, is one of the most popular fruits worldwide. The demand for specific knowledge of metabolism in strawberries is increasing. This knowledge is applicable for genetic studies, plant breeding, resistance research, nutritional science, and the processing industry. The molecular basis of strawberry aroma has been studied for more than 80 years. Thus far, hundreds of volatile organic compounds (VOC) have been identified. The qualitative composition of the strawberry volatilome remains controversial though considerable progress has been made during the past several decades. Between 1997 and 2016, 25 significant analytical studies were published. Qualitative VOC data were harmonized and digitized. In total, 979 VOC were identified, 590 of which were found since 1997. However, 659 VOC (67%) were only listed once (single entries). Interestingly, none of the identified compounds were consistently reported in all of the studies analyzed. The present need of data exchange between "omic" technologies requires high quality and robust metabolic data. Such data are unavailable for the strawberry volatilome thus far. This review discusses the divergence of published data regarding both the biological material and the analytical methods. The VOC extraction method is an essential step that restricts interlaboratory comparability. Finally, standardization of sample preparation and data documentation are suggested to improve consistency for VOC quantification and measurement.

The Terpene Synthase Gene Family of Carrot (Daucus carota L.): Identification of QTLs and Candidate Genes Associated with Terpenoid Volatile Compounds.

Terpenes are an important group of secondary metabolites in carrots influencing taste and flavor, and some of them might also play a role as bioactive substances with an impact on human physiology and health. Understanding the genetic and molecular basis of terpene synthases (TPS) involved in the biosynthesis of volatile terpenoids will provide insights for improving breeding strategies aimed at quality traits and for developing specific carrot chemotypes possibly useful for pharmaceutical applications. Hence, a combination of terpene metabolite profiling, genotyping-by-sequencing (GBS), and genome-wide association study (GWAS) was used in this work to get insights into the genetic control of terpene biosynthesis in carrots and to identify several TPS candidate genes that might be involved in the production of specific monoterpenes. In a panel of 85 carrot cultivars and accessions, metabolite profiling was used to identify 31 terpenoid volatile organic compounds (VOCs) in carrot leaves and roots, and a GBS approach was used to provide dense genome-wide marker coverage (>168,000 SNPs). Based on this data, a total of 30 quantitative trait loci (QTLs) was identified for 15 terpenoid volatiles. Most QTLs were detected for the monoterpene compounds ocimene, sabinene, ß-pinene, borneol and bornyl acetate. We identified four genomic regions on three different carrot chromosomes by GWAS which are both associated with high significance (LOD ≥ 5.91) to distinct monoterpenes and to TPS candidate genes, which have been identified by homology-based gene prediction utilizing RNA-seq data. In total, 65 TPS candidate gene models in carrot were identified and assigned to known plant TPS subfamilies with the exception of TPS-d and TPS-h. TPS-b was identified as largest subfamily with 32 TPS candidate genes.

Validation of a PCR test to predict the presence of flavor volatiles mesifurane and γ-decalactone in fruits of cultivated strawberry (Fragaria × ananassa).

Flavor improvement is currently one of the most important goals for strawberry breeders. At the same time, it is one of the most complex traits to improve, involving the balanced combination of several desired characteristics such as high sweetness, moderate acidity, and the appropriate combination of aroma compounds that are beginning to be delineated in consumer tests. DNA-informed breeding will expedite the selection of complex traits, such as flavor, over traditional phenotypic evaluation, particularly when markers linked to several traits of interests are combined during the breeding process. Natural variation in mesifurane and γ-decalactone, two key volatile compounds providing sweet Sherry and fresh peach-like notes to strawberry fruits, is controlled by the FaOMT and FaFAD1 genes, respectively. In this study, we have optimized a simple PCR test for combined analysis of these genes and determined a prediction accuracy above 91% using a set of 71 diverse strawberry accessions. This high accuracy in predicting the presence of these important volatiles combined with the simplicity of the analytical methodology makes this DNA test an efficient tool for its implementation in current strawberry-breeding programs for the selection of new strawberry cultivars with superior flavor.

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, ß-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 ß-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.

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.

Variation in the amounts of selected volatiles in a model population of fragaria × ananassa Duch. As influenced by harvest year.

Volatile metabolites are a basis for sensory and resistance traits of Fragaria × ananassa . Stability of expression is important for the selection of cultivars. For the first time, the stability of volatiles in a strawberry population after cross-combination of two distinct cultivars ('Mieze Schindler' × 'Elsanta') has been investigated. In this work, environmentally caused variations in the synthesis of 18 volatiles were studied over two years using a model population of 158 clones. The stability varied throughout the F1 seedling population between the two years, defining stable and unstable genotypes with respect to volatile synthesis. Most of the stable genotypes exhibited low values in relative volatile concentration. Merely 6 stable volatiles were detected in the parental cultivars, whereas about 40% of the F1 progeny had up to 11 stable volatiles. Consequently, a higher stability in volatile synthesis can be achieved by breeding.

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

One 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.

Sensory and quality analysis of different melon cultivars after prolonged storage.

The purpose of this work was to evaluate the sensory and general quality of four different melon cultivars (Cucumis melo L.) immediately after harvest and at the end of storage and marketing simulation. After 16 days of storage at 5 degrees C and additional 3 days at 20 degrees C, only cultivar 'C-8' had a poor general appearance due to significant low firmness and relatively high decay incidence compared to the cultivars '5080', 'Ideal' and '7302'. The cultivar '7302' was found to have the higher overall quality. The human-sensory and organoleptic analyses revealed that the cultivars can be differentiated on the basis of retronasal odour. The texture of the melons seems to be dependent on the genotype. All the complex perceptions analysed in this work contribute to the acceptability, which is in the fresh fruits of '7302' the best and in 'Ideal' the worst. After storage and marketing simulation 'Ideal' and 'C-8' are no longer favoured, but '5080' and '7302', despite different characters, were found to be similarly accepted. It can be concluded that with the aid of the human-sensory method developed to characterize the melon varieties it is possible to distinguish the different genotypes.

Rapid differentiation of new apple cultivars by headspace solid-phase microextraction in combination with chemometrical data processing.

The aim of this study was to test a combination of automated headspace solid phase-microextraction gas chromatography (GC) with chemometrical data treatment for the rapid differentiation of enzyme-inactivated homogenates of new apple cultivars. The four cultivars Pinova, Piflora, Renora and Florina are characterized by different volatile patterns. Differences in the contents of volatiles were especially found for butyl acetate, ethyl butanoate, 2-methyl butanol, ethyl acetate and 6-methyl-5-hepten-2-ol. The used sample preparation method for GC coupled with pattern recognition of chromatograms is a useful tool for rapid and reliable determination of large numbers of samples.