Insights into the chemosensory basis of flavor in table grapes.

BACKGROUND: The full flavor of grape berries is determined by the interaction of sugars, acids, volatile compounds, and other berry properties, such as astringency. Sugars and acids are important for berry taste, whereas volatile compounds are important for the unique berry flavors, e.g., monoterpenes for the Muscat varieties. RESULTS: We explored the basis for 'fruity' flavor perception in table grapes. Samples were collected from 134 new table grape lines and commercial varieties and tested chemically for their volatile profiles and organoleptically by tasting panels. At the sensory level, flavor impression was strongly correlated with berry preference, whereas among 'fruity', 'neutral', 'herbaceous,' and 'Muscat', only the 'fruity' flavor was correlated with berry preference. At the chemical level, 114 volatile compounds were detected in the 81 breeding lines and cultivars examined, and grouped into 'core' and 'unique' categories. The typical berry flavor seemed to depend on the major volatile aldehydes - 1-hexanal and (E)-2-hexenal - accounting for up to an average 85% of the berry's core volatile concentration. We found four volatile compounds - α-bergamotene, geranyl formate, aristolene and α-penansinene - previously undetected, to our knowledge, in fresh grape berries. CONCLUSIONS: High 'fruity' flavor scores were related to three independent factors: (i) presence of unique volatile compounds, such as the sesquiterpene α-copaene, (ii) higher total concentration of volatile compounds, (iii) optimal maturity associated to high total soluble solids (TSS) levels, interacting with berry volatile composition. These combined sensory and analytical data on the flavor of table grapes improve our understanding of the complex interface between chemical and sensory perception in fruit. © 2019 Society of Chemical Industry.

The ubiquitin extension protein S27a is differentially expressed in developing flower organs of Thompson seedless versus Thompson seeded grape isogenic clones.

In Vitis vinifera L. cv. Thompson Seedless, fertilization occurs but seeds abort, a type of stenospermocarpy. To clone transcripts with differential expression during flower development, suppressive subtractive hybridization was carried out using two isogenic clones 'Thompson seedless' and 'Thompson seeded', at three stages of inflorescence development (from bud break to ~20 days prior to anthesis). Differential screening and sequencing of a forward and reverse subtractive cDNA library yielded several singleton ESTs. One differentially expressed clone in 'Thompson' seeded versus seedless isogenic clones was the ubiquitin extension protein S27a. In situ hybridization demonstrated its significantly higher expression in the carpel and ovaries of 'Thompson' seedless versus seeded isogenic clones during flower development. Overexpression of this gene resulted in abnormal plant regeneration and inhibited shoot development compared to controls; its silencing in embryogenic callus induced cell necrosis and callus death, evidencing tight regulation of this gene in developing organs of grape. S27a overexpression in carpels and integuments of the seedless flower may interfere with normal development of these organs, leading to embryo abortion and seedlessness.