Graduate Thesis Or Dissertation
 

Sensory Analysis and Genetic Mapping of Green Bean Flavor

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  • Green bean flavor has been studied since the 1960’s to better understand Blue Lake flavor in processed green beans in Oregon. Research by Stevens and colleagues showed that Blue Lake flavor could be reconstituted in a bland bean by adding 0.4ppm of 1-octen-3-ol and 1.6ppm of 3-hexen-1-ol. These two volatile compounds are derived from fatty acid metabolism with the key enzymes being a lipoxygenase, a hydroperoxide lyase, and an alcohol dehydrogenase. They also showed that another important class of green beans, the Tendercrop green beans, could be reconstituted with the addition of 0.2ppm of linalool. This volatile compound is derived from the terpenoid pathway, and the key enzymes are geranyl pyrophosphate synthase and linalool synthase. Early work into the genetics of flavor in green beans seemed to show that a relatively small number of genes were involved in the production of linalool and 1-octen-3-ol, but no attempt was made to map these genes. With the advent of the common bean genome (Phaseolus vulgaris L.) and associated molecular tools, such as the microarray single nucleotide polymorphism (SNP) chip, it has become possible to map the genes involved in flavor production in green beans. To better understand the relationship of these compounds to sensory descriptors, a sensory analysis of 205 green bean varieties by eleven panelists was conducted in which the measured levels of linalool and 1-octen-3-ol were correlated to eight sensory descriptors. Measurements of volatile levels were taken using head space analysis on a gas chromatography – mass spectrometry (GC-MS) instrument. The results showed a correlation between linalool and the floral descriptor and 1-octen-3-ol and the nutty descriptor. The results also showed a negative correlation between linalool and 1-octen-3-ol. Linkage mapping with QTL analysis was then conducted. Linkage mapping utilized a biparental cross between a bland bean, ‘Serin’, and a more flavorful bean, ‘OR5630’. One hundred forty progeny were maintained through single seed descent to the F7 generation. The progeny were genotyped with an Illumina Infinium Genechip BARCBEAN6K_3 SNP microarray. A linkage map was generated and Multiple QTL Models (MQM) analysis was conducted to identify Quantitative Trait Loci (QTL). Six QTL were identified for linalool, three for 1-octen-3-ol, and three for 3-hexen-1-ol. In addition to linkage mapping and QTL analysis, a Genome Wide Association Study (GWAS) was conducted utilizing the Fixed and random model Circulating Probability Unification (FarmCPU) method. GWAS provides higher resolution than linkage mapping but cannot map rare alleles. GWAS analysis was conducted on a diverse panel of 201 green bean varieties, including numerous landraces, commercial pure lines, and heirloom beans. A correction for population structure was made by the addition of one principal component to the model. This principal component reflected the divide in all common bean lines between the Mesoamerican and Andean lineages. GWAS analysis identified 27 significant associations above a Bonferroni threshold for eight volatile compounds, including linalool, 1-octen-3-ol, 3-hexen-1-ol, hexanal, 1-hexanol, 1-penten-3-ol, 1-penten-3-one, and β-ionone. A cluster of alcohol dehydrogenase genes is located within 0.58Mb to significantly associated SNPs for hexanal and 1-hexanol and is located within 1.75Mb to a significantly associated SNP for 3-hexen-1-ol. This cluster of genes may be candidate genes for these SNPs because alcohol dehydrogenase genes are involved in the biosynthetic production of these compounds.
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  • 2018-03-22 to 2019-04-22

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