Volatile compounds are responsible for the aroma and contribute to the flavor of fresh strawberries (Fragari×anannassa), red raspberries (Rubus idaeus), and blueberries (Vaccinium sp.). Strawberry aroma is composed predominately of esters, although alcohols, ketones, and aldehydes are also present in smaller quantities. The aroma of raspberries is composed of a mixture of ketones and terpenes. In highbush blueberry (Vaccinium corymbosum), aroma is dominated by aromatic hydrocarbons, esters, terpenes and long chain alcohols, while in lowbush blueberries (Vaccinium angustifolium), aroma is predominated by esters and alcohols. The composition and concentration of these aroma compounds are affected by cultivar, fruit maturity, and storage conditions. Volatile composition varies significantly both quantitatively and qualitatively among different cultivars of small fruit. As fruit ripen, the concentration of aroma volatiles rapidly increases closely following pigment formation. In storage, volatile concentrations continue to increase but composition depends on temperature and atmosphere composition. Many opportunities exist to improve the aroma volatile composition and the resulting flavor of small fruit reaching the consumer.
Stanley J. Kays, Yan Wang and Wayne J. McLaurin
Sweetness, which is known to vary significantly among clones, is the dominant sensory attribute characterizing the flavor of sweetpotatoes [Ipomoea batatas (L.) Lam.]. The relative sweetness of baked roots, expressed as sucrose equivalents, was determined for 272 clones from the U.S. Department of Agriculture National Plant Germplasm System collection. The clones were from 34 countries that collectively produced 93% of the world's sweetpotato production in 2002. Individual clones were separated into five categories based upon the concentration and relative sweetness of individual sugars, expressed numerically as sucrose equivalents per 100 g dry mass: very high ≥38; high 29-37; moderate 21-28; low 12-20; and nonsweet ≤12. Based upon the mean sucrose equivalents of the clones for each country, only 9% of the countries, which accounted for only 2.1% of the total annual production of the countries surveyed, had sweetpotatoes that were classified as very high. While the majority (62%) of the countries surveyed had clones that were categorized as high, they represented only 4.4% of the total production of sweetpotatoes. None of the countries had mean sucrose equivalent values that were categorized as low or nonsweet, although a few individual clones were ranked as low and one as nonsweet. Countries that account for the majority (87%) of the sweetpotatoes grown worldwide had a mean sucrose equivalent ranking of moderate. Sweetness is derived from the composite of endogenous sugars (sucrose, glucose, fructose) and maltose formed via starch hydrolysis during baking. Maltose accounted for only 42% of the average contribution to the total sucrose equivalents. The range in the concentration of individual sugars among clones was substantial as was their contribution to sucrose equivalents. Sucrose equivalents due to maltose in individual clones ranged from 0.6 to 21.9 while endogenous sugars ranged from 6.4 to 46.9. The results indicate that essentially all of the sweetpotato clones tested from around the world were classified as equal to or greater than moderate in sucrose equivalents, and that there is substantial genetic diversity within the genepool such that the potential exists for tailoring the flavor of new cultivars, via significantly increasing or decreasing sugar content, to meet specific consumer preferences and/or product uses.
Dangyang Ke and Adel A. Kader
`Valencia' oranges [Citrus sinensis (L.) Osbeck] tolerated up to 20 days of exposure to 0.5%, 0.25%, or 0.02% O2, at 5 or 10C followed by holding in air at 5C for 7 days without any detrimental effects on external and internal appearance. Oranges stored in 0.5%, 0.25%, or 0.02% O2 had lower respiration rates, but higher resistance to CO, diffusion and higher ethanol evolution rates than those stored in air at 10C. Similar, but less pronounced, effects of the low O2 atmospheres were observed at O and SC. Respiration rates, internal CO2 concentrations, and ethanol evolution rates were generally higher at 10C than at 0C, while resistance to CO2 diffusion was lower at the higher temperature. `Valencia' oranges kept in 60% CO2 at 5C for 5 to 14 days followed by holding in air at 5C for 7 days developed slight to severe injury that was characterized by skin browning and lowered external appearance scores. Juice color, soluble solids content, pH, titratable acidity, and ascorbic acid content were not significantly influenced by either the low O2 or the high CO2 treatments. However, these treatments increased ethanol and acetaldehyde contents, which correlated with the decrease in flavor score of the fruits. Ethanol content of the oranges transferred to air following low 02 treatment correlated with CO2 production rate of the fruits at the transfer temperature and was related to ethanol evolution and probably production rates after the transfer.
David E. Kopsell, William M. Randle and Mark A. Eiteman
Onion (Allium cepa L.) pungency changes during storage. To better understand these flavor changes, seven onion cultivars representing different storage duration, photoperiodic requirement, and flavor intensity were greenhouse grown and the bulbs stored for 3 or 6 months at 5±3 °C, 0.8 to 1.1 kPa vapor pressure deficit. Bulbs were evaluated using high-pressure liquid chromatography quantification for changes in S-alk(en)yl cysteine sulfoxide (ACSO) flavor precursors and γ-glutamyl peptide (γ-GP) biosynthetic intermediates before storage and monthly thereafter. Before and during storage, cultivars differed in total ACSO, (+) S-methyl-L-cysteine sulfoxide (MCSO), trans-(+)-S-(1-propenyl)-L-cysteine sulfoxide (PRENCSO), (+) propyl-L-cysteine sulfoxide (PCSO), S-2 carboxypropyl glutathione (2-CARB), and γ-L-glutamyl-S-(1-propenyl)-L-cysteine sulfoxide (γGPECSO) concentration. During storage MCSO generally decreased while PRENCSO increased in concentration for most cultivars. The linear increase in PRENCSO concentration during storage was accompanied by a linear decrease in γGPECSO concentration. While not measured in this study, these trends indicate γ-glutamyl transpeptidase activity throughout bulb storage. γ-Glutamyl transpeptidase was previously reported to be active only in the later stages of bulb storage or during bulb sprouting. Changes in ACSO and γ-GP compounds during storage did not follow previously reported changes during storage for enzymatically formed pyruvic acid (EPY) for these cultivars. To better understand what causes flavor changes in onions during storage, future investigations should include analysis of the enzymes involved in flavor development and ACSO hydrolysis products.
P. Perkins-Veazie and J.K. Collins
Small fruit are rich in several types of phytochemicals, vitamins, and minerals. These compounds have health functional properties that may protect humans from cardiovascular disease and certain cancers. Several of these phytochemicals, such as dietary fiber, anthocyanins, and polyphenolics, also contribute to small fruit quality. Other components contribute to appearance and taste. Nonvolatile organic acids contribute to the perceived sourness of small fruit and changes in levels can alter visual color by affecting cellular pH and anthocyanin structure. The soluble sugars glucose, fructose, and sucrose contribute directly to the perceived sweetness of the fruit and provide carbohydrates for other metabolic functions such as phenolic and ascorbic acid synthesis.
John C. Beaulieu
Examples from various harvest regimes, storage regimes, cultivars and different packaging methods are presented to characterize volatile ester differences after cutting and how changes occur in characteristic flavors throughout the postharvest life of certain cut fruit products. In many fresh-cut cantaloupe cultivars and in honeydew, there was a relative increase in nonacetates and coinciding relative decrease in acetates during storage. A similar and consistent nonacetate:acetate ester ratio was conserved in cantaloupe from eastern and western U.S. regions, as well as different cultivars from the same field. Furthermore, similar ratios were observed in many melon cultivars over multiple years from different seasons and growing regions. Since many cultivars exhibited similar trends in 2-year repeated studies, the trend is apparently independent of year and season. Fresh-cut `Gala' apples, on the other hand, displayed a slightly different trend whereby both acetates and nonacetate esters decreased appreciably during storage. The hypothesis is put forward that recycling of esters during storage in certain fresh-cut fruits disturbs the delicate fine balance of characteristic volatiles. Consistently decreasing acetates along with increasing nonacetates could alter the overall perceived desirable flavor attributes during fresh-cut melon storage, even though volatile esters are still abundant.
Jyh-Bin Sun, Ray F. Severson and Stanley J. Kays
We describe a relatively simple collection procedure for quantifying volatiles in baked sweetpotato [Ipomoea batatas (L.) Lam.]. Volatiles formed during baking `Jewel' and `Centennial' sweetpotatoes at 204C were purged from a baking vessel with He or a HeO2 mixture, collected in cold methylene chloride, and reduced in volume using a Kuderna-Danish concentrator. Volatile components were quantified by capillary gas chromatography and characterized using gas chromatographic-mass spectrometer analysis. Quantitatively, the major components were identified as 2-furaldehyde; 2-furanmethanol; benzaldehyde; 5-methyl-2-furfural; phenylacetaldehyde; 3-hydroxy-2-methyl-4 H -pyran-4-one; 2,3-dihydro-3,5-dihydroxy-6-methyl-4 H- pyran-4-one; and 5-hydroxy-methyl-2-furancarboxaldehyde. Some quantitatively minor compounds were also identified. The volatile collection system is reproducible for quantitative comparisons among breeding lines.