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Fernando Maul, Steven A. Sargent, Elizabeth A. Baldwin and Charles Sims

`Agriset-761' and `CPT-5' tomato fruits were harvested at green stage and subsequently exposed to a postharvest exogenous ethylene-air mixture (100 ppm C2H4 at 20°C). Tomatoes with visual symptoms of ripening (breaker stage = <10% red coloration) were removed from ethylene treatment after 1, 3, and 5 days and were transferred to 20°C and 85% RH. At “table-ripe” stage (full red coloration and 4-mm fruit deformation after 5 sec@9.8N), whole fruit samples were analyzed for difference/discrimination sensory evaluations, aroma volatile profiles, and chemical composition. Flavor of fruits gassed for 1 day was rated significantly different than that of fruits gassed for 3 or 5 days (n = 25 panelists) for both cultivars. Several panelists noted the perception of “rancid” and “metallic” tastes, and “lingering” aftertaste in fruits gassed for 5 days. Chemical composition assays showed that flavor differences could be partially due to a significant increase in pH values between fruits gassed for 1 and 5 days (4.23 and 4.34, respectively for `Agriset-761') and a significant decrease in titratable acidity (0.91% and 0.73%, respectively, for `Agriset-761'; 1.04% and 0.86%, respectively, for `CPT-5'). No significant differences in soluble solids content or total sugars were found in any treatments for either cultivar. `Agriset-761' showed significant increases in the concentrations of acetone, hexanal, 2+3 methylbutanol, and a decrease in 2-isobutylthiazole, whereas, `CPT-5' fruits showed significant increases in hexanal, 2+3 methylbutanol, trans-2-heptenal, 6-methyl-5-hepten-2-one, 2-isobutylthiazole, β-ionone, geranylacetone, and a decrease is ethanol concentration. In both cultivars, these significant differences in important aroma volatile compounds could be of enormous relevance in the perception of off-flavor/off-odors.

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Marisa M. Wall and Joe N. Corgan

Individual onion (Allium cepa L.) bulbs were evaluated for pungency by measurement of enzymatically produced pyruvate and by flavor perception. In four separate experiments, pyruvate values were highly and significantly correlated to mean sensory ratings. Correlation coefficients (r) were 0.92, 0.84, 0.95, and 0.79, and regression coefficients (R2) were 0.84, 0.71, 0.91, and 0.62. The high correlations indicate that pyruvate analysis can be used as a reliable selection technique for pungency in onion breeding programs.

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John A. Juvik

Investigating the chemical constituents that determine human preferences for cooked vegetable flavor and aroma is complicated by experimental limitations. Several to many biochemicals interact with each other and with textural properties to influence perception of eating quality. This is particularly true for volatile compounds associated with aroma, where differences in concentration, volatility, reactivity, chemical stability, thresholds of perception, and duration of receptor bonding generate transient stimuli that are integrated into the sensory evaluation of quality. This paper describes methodology that can isolate, identify, and quantify the effect of chemical constituents that influence flavor and aroma using populations segregating for genes controlling eating quality. A F2:3 population derived from a cross between two sweet corn inbreds that differed in kernel characteristics associated with eating quality were assayed for variation in chemical, physical, and sensory characteristics. Because most aromatic constituents of sweet corn are generated during cooking, kernel tissue samples were autoclaved and analyzed by gas chromatography. Panel variation in sample preference were found to be controlled by three overlying factors—taste, texture, and aroma—the relative importance of each being 45.1%, 30.5%, and 24.4%, respectively. DNA marker technology was employed to generate a linkage map of this population that was sufficiently saturated with probes to allow for the identification and mapping of genes controlling each characteristic. This information improves selection methodology in a breeding program aimed to develop germplasm with superior eating quality.

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Elhadi M. Yahia

The effectiveness of some poststorage treatments in enhancing the flavor components of low-ethylene controlled-atmosphere (LCA) stored `McIntosh' apples (Malus domestica Borkh.) was investigated. Fruits were stored for 9 months in LCA at 3.3C and then exposed to air at 20C and to air, simulated LCA, 100% O2, or light at 3.3C for up to 4 weeks. Respiration and ethylene production indicated that apples were still in the early stage of ripening after 9 months of storage in LCA. Gas chromatographic analysis for 13 odor-active volatiles revealed the presence of eight. Air at 20C after LCA significantly increased the production of some odor volatiles, while light for up to 3 weeks only slightly increased their concentration. Poststorage exposure to air or 100% O2 at 3.3C for up to 4 weeks was not effective in enhancing volatile formation.

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W.M. Randle, D.A. Kopsell, D.E. Kopsell, R.L. Snyder and R. Torrance

The marketing of onions (Allium cepa L.) based on bulb pungency as a measure of overall flavor intensity is being considered by the onion industry. Pungency is highly variable within and among fields due to genetic and environmental factors. Therefore, a study was undertaken to develop a sampling procedure to estimate onion pungency means and variances from field-grown onions with predetermined degrees of accuracy and confidence. Two shortday onion cultivars, commonly grown in the Vidalia, Ga., area, were each randomly sampled from four different fields. The sampled bulbs were analyzed for enzymatically formed pyruvic acid (EPY) and soluble solids content (SSC) to assess pungency and sugars, respectively. EPY concentration and SSC varied between the two cultivars, among the four fields within cultivars, and among the fifty samples within each field. In a combined analysis of all eight fields, at least 1.3 ten-bulb samples would be needed per acre to come within ±0.5 μmol EPY of a field's true EPY mean with 95% confidence. If the accuracy of the estimation was lowered to ±1.0 μmol EPY of a field's true mean, then at least 0.4 ten-bulb samples would be needed per acre. Because SSC was less variable than EPY, the number of ten-bulb samples needed per acre to estimate a field's true mean was lower than the number required to estimate EPY. Establishing a sampling method to estimate an onion field's EPY and SSC will provide the mechanism to standardize onion flavor in the market place and instill greater consumer confidence in purchasing onions.

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John K. Fellman

Volatile ester molecules are important contributors to the perception of fruit taste. Biosynthesis of volatile compounds occurs via several biochemical pathways. Ongoing studies have concentrated on alcohol acetyl transferase, the terminal step in the acetate ester synthesis pathway. Our studies on volatile biosynthesis in apples have revealed several interesting phenomena. First, the nature and amount of volatile compounds are cultivarand strain-dependent. Studies with `Delicious' show a relationship between amount of peel coloration and flavor volatile content of tissue. Second, it is possible to manipulate the preharvest growing environment to influence the content of some volatiles in the fruit. Third, generation of volatiles is closely linked to the onset of climacteric ripening. Other experiments show the response of apples to different storage conditions with regard to volatile ester synthesis. In some cultivars softening apparently provides ester precursor molecules, leading us to speculate that there are glycosidically bound intermediates that are liberated by the action of cell-wall degradation.

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James Mattheis and John K. Fellman

The commercial use of modified atmosphere packaging (MAP) technology provides a means to slow the processes of ripening and senescence during storage, transport, and marketing of many fresh fruit and vegetables. The benefits of MAP and controlled atmosphere (CA) technologies for extending postharvest life of many fruit and vegetables have been recognized for many years. Although both technologies have been and continue to be extensively researched, more examples of the impacts of CA on produce quality are available in the literature and many of these reports were used in development of this review. Storage using MAP, similar to the use of CA storage, impacts most aspects of produce quality although the extent to which each quality attribute responds to CA or modified atmosphere (MA) conditions varies among commodities. Impacts of MAP and CA on flavor and aroma are dependent on the composition of the storage atmosphere, avoidance of anaerobic conditions, storage duration, and the use of fresh-cut technologies before storage.

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D.A. Smith, M.L. Metz and S.L. Cuppett

Dry edible beans (Phaseolis vulgaris) represent an inexpensive way to incorporate protein into the diet as a food ingredient, but beans contain unpleasant flavors and several anti-nutritional factors that limit their use without first processing with long heat treatments. `Great Northern' bean flour was processed using either static or specially designed dynamic (continuous) processing methods. The dynamic process treated flour slurries at temperatures up to 124°for 20 sec. The slurries were quick-frozen and freeze-dried after frozen storage periods of 0, 8, 24, 120, or 504 hr. The flours were analyzed for sensory properties, emulsifying activity, foaming properties, and trypsin inhibition. The heat treatments improved sensory attributes of the flour. The foam capacity and foam stability decreased in heat-treated flours. Trypsin inhibitor activity was at a minimum level immediately following thermal processing, but increased with time in frozen storage prior to drying. Minimal thermal processes cannot be relied upon to inactivate trypsin inhibitors.

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A. Plotto, M.R. McDaniel and J.P. Mattheis

`Gala' is an early season apple variety that has a distinctive aroma and flavor. Studies were conducted to identify volatile compounds that contribute to `Gala' aroma. `Gala' apples were harvested at optimum maturity in a commercial orchard. Volatile compounds were trapped on activated charcoal using dynamic headspace sampling and eluted with carbon disulfide. Odor profiles of the samples were determined using OSME, a method developed at Oregon State Univ. that combines gas chromatography and olfactometry with a time-intensity scale. Three trained panelists described odor characteristics of compounds eluted through a sniff port of a gas chromatograph. Compounds were identified by matching Kovats indices with those of standards and also by mass spectrometry. Butyl acetate, 2-methyl butyl acetate, and pentyl acetate were characteristic of `Gala' apple. Methyl-2-methyl butyrate, ethyl-2-methyl butyrate, pentyl acetate, and butyl-2-methyl butyrate carried apple-like descriptors.

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Chuck A. Ingels, Gale H. McGranahan and Ann C. Noble

To determine if flavor differences could be detected among several Persian walnut (Juglans regia L.) cultivars, difference tests with eight cultivars were conducted using the duo-trio method. No differences were found when `Hartley' was compared to `Vina', `Scharsch Franquette', and `Mayette'. However, `Chandler', `Chico', `Howard', and `Sunland' were significantly different, and paired comparisons were then used to test these cultivars against `Hartley' in terms of several flavor characteristics. No differences in astringency and “walnut flavor” were detected; however, `Chandler' was judged to be sweeter than `Hartley', which was sweeter than `Howard'. `Chico' was found to be the firmest cultivar.