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United States Department of Agriculture

Agricultural Research Service

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Research Project: CHEMICAL, GENETIC AND CONSUMER PROFILING OF HEIRLOOM TOMATOES - THE UNDERLYING CHEMISTRY OF A GREAT TASTING TOMATO

Location: Plant Genetic Resources

2013 Annual Report


1a.Objectives (from AD-416):
We will screen flavor chemical composition and conduct consumer evaluation (taste tests) for 27 heirloom varieties of tomato. Fruits will be brought to the laboratory for physicochemical, sensory, and consumer preference measurements. Flavor is one of the most highly demanded consumer traits of tomato at present, and the lack of flavor is one of the most commonly heard complaints associated with modern varieties of tomato.


1b.Approach (from AD-416):
Previously 27 heirloom varieties of tomato were evaluated and this project will complete the evaluation of another 27 heirloom varieties to give a dataset for 74 heirloom tomatoes. Since flavor is the major concern of fresh market tomato, germplasm used is primarily from fresh market tomatoes.

Tomato seeds were obtained from Seeds of Change (Santa Fe, NM), Totally Tomatoes (Randolph, WI) or Victory Seed Co. (Molalla, OR). Most varieties selected are described as heirloom, open-pollinated. A few modern hybrid varieties Tasti-Lee, Florida 47) were also selected for comparison. Plants will be grown in the field at the University of Florida North Florida Research and Education Center-Suwannee Valley in the spring or fall seasons. Plants will be grown using commercial Florida protocols, i.e., raised beds with plastic mulch, drip irrigation and staking. Depending on the variety, a minimum of 50 plants separated into six plant randomized blocks will be grown.

Volatile compound identification is determined by GC-MS and coelution with known standards (Sigma-Aldrich, St. Louis, MO). We routinely quantify ~60 volatiles (Table 1), including all of the compounds believed to significantly contribute to tomato flavor. Sugars, acids, glutamic acid and Brix are determined as described in Vogel et al. (2010). Samples are analyzed using citric acid, malic acid, glutamic acid and glucose/fructose analysis kits (R-Biopharm, Marshall, MI, USA) according to the manufacturer’s instructions. Average values are calculated from five biological replicates. Soluble solids ('Brix) are measured using a handheld refractometer.

Fully ripe fruit are harvested for taste panels. Any fruits with defects are culled out. A random subset of the fruit is selected for biochemical analysis. A group of 100 tomato consumers are recruited for each season to evaluate all the varieties. All panelists go through a training session to familiarize them with the scaling and procedures. Tomatoes are sliced into wedges (or in halves for grape/cherry types) and each panelist is given two pieces for evaluation. Where appropriate, color differences can be masked with artificial lighting. Panelists rate their overall liking as well as their liking for the texture on a hedonic scale. This scale assesses the liking for tomatoes in the context of all pleasure/displeasure experiences: 0=neutral, -100=strongest disliking of any kind experienced, and +100=strongest liking of any kind experienced. Panelists then rate their perceived intensities of overall tomato flavor, sweetness, sourness, saltiness and umami. This scale assesses taste and flavor sensations in the context of all sensory experience: 0=no sensation, 100=strongest sensation of any kind experienced. The scales were devised to provide valid comparisons across subjects and sessions and the method has proven to be highly reproducible in comparing many varieties over multiple seasons.


3.Progress Report:

We proposed to conduct full flavor chemical analysis on a set of 27 varieties of tomatoes. As many as possible would be also profiled in consumer preference panels. Of the 27, the only variety that we have failed to complete a consumer panel on is German Queen. We simply could not get enough ripe fruit for a 100 person panel on a single day due to the low yields and extremely short shelf life of the fruits. Other than German Queen we have completed the stated objectives. We must note that three of the varieties are being retested in our spring plantings for reasons described below.

Some of the results were incorporated into a paper that was published in 2012 (Tieman et al., Current Biology 22:1-5). Most of these data were collected after the acceptance of that paper and remain unpublished. In order to get the results disseminated rapidly to the public, we have summarized the consumer liking scores of many of the results at our web site (http://www.hos.ufl.edu/kleeweb/varietytrials.html). This resource has been widely viewed by the public and is an impartial source of information on heirloom flavor. We intend to publish all of the chemical and consumer data in a refereed journal after we have analyzed it. We expect to be able to submit a paper by the end of 2013 with a complete summary.

During the review process, it was noted that even though we purchased seeds of many of these varieties from commercial seed companies, the identities of the materials might not match the identities of previously deposited lines. The names of approximately a dozen lines that we were testing matched with lines already deposited at Geneva or the TGRC. For these varieties, we obtained seeds from the stock centers, grew them side by side with our materials, and subjected them to analysis with 34 CAPS markers. All but three of the lines were perfectly matched. Our analyses revealed differences in Stone, Early Red Chief and Gulf State Market. We are now growing out the stock center materials to repeat chemical and consumer tests. These experiments will be completed by the end of summer 2013. Finally, we provided a seed of every variety that we tested that was not already deposited to the USDA seed repository in Geneva NY.


Last Modified: 9/21/2014
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