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Jyh-Bin Sun, Ray F. Severson, William S. Schlotzhauer and Stanley J. Kays

Thermal degradation of fractions from sweetpotato roots (`Jewel') was conducted with gas chromatographymass spectrometry to identify precursors of critical flavor volatiles. Upon heating (200 C), sweetpotato root material that was insoluble in methanol and methylene chloride produced similar volatile profiles to those from sweetpotatoes baked conventionally. Volatiles derived via thermal degradation of the nonpolar methylene chloride fraction and the polar methanol fraction did not display chromatographic profiles similar to those from conventionally baked sweetpotatoes. Initial reactions in the formation of critical volatiles appear to occur in the methanol and methylene chloride insoluble components. Maltol (3-hydroxy-2-methyl-4-pyrone) was found to be one of the critical components making up the characteristic aroma of baked sweetpotatoes. Integration of an analytical technique for the measurement of flavor into sweetpotato breeding programs could potentially facilitate the selection of improved and/or unique flavor types.

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Weimin Deng and Randolph M. Beaudry

Sampling factors that could affect gas chromatograph (GC) response for volatile analysis such as syringe pumping time, injection volume, needle length, temperature, and the type of volatile were investigated. Capillary GC column segments (steel and glass) were installed in gas-tight syringes and used as needles for volatile analysis. Standard stainless-steel needles were also used. Hexylacetate, ethyl-2-methylbutyrate, 6-methyl-5-hepten-2-one, and butanol standard were measured. The number of pumps required to maximize GC response for each needle–volatile combination was determined. Maximal GC response for hexylacetate using standard stainless steel, capillary glass, and capillary steel needles required 10, 20 and 30 pumps, respectively. However, for butanol measurement, the optimal syringe pump number was 5 to 10 for all needle types. The use of a capillary needle resulted in an increase in GC response in the range of 3- to 15-fold relative to a standard stainless steel needle. Injection volume affected GC response in a needle-and volatile-dependent manner. In no case did injection volume vs. GC response extrapolate through origin. The GC response for capillary column needles increased as temperature decreased. Capillary column needles may be useful tools for analysis of volatiles that readily partition into the column coating.

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Charles F. Forney

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.

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Ezzedine Derbali, Louis-Philippe Vezina and Joseph Makhlouf

Objectionable off-odors are produced by broccoli (Brassica oleracea, L.) when it is held under anaerobic conditions. These off-odors were attributed to sulfur volatile compounds mainly methanethiol (MT) and hydrogen sulfide. The present study was undertaken to investigate the effects of anaerobic conditions on the metabolism and emission of sulfur volatiles by broccoli. Inhibition assays using aminooxyacetic acid (AOA)—a potential inhibitor of pyridoxal-phosphate-dependent enzymes-confirmed the enzymatic origin of these volatiles. However, anaerobic atmosphere had no inducible effect on the enzymes cystine lyase, cysteine desulfhydrases and S-alkylcysteine lyase. These pyridoxal-phosphate-dependent enzymes thought to catalyze the respective degradation of cystine, cysteine and S-methyl-L-cysteine to sulfur volatiles showed no significant activity increase. Storage of sterile broccoli seedlings under anaerobic atmosphere resulted in an important increase of the content of sulfur amino acids that corresponded to an increased emission of sulfur volatiles. Cysteine and methionine content increased particularly at 24 hours and decreased later. Whereas, S-methyl-L-cysteine content increase was more obvious after 48 hours. The results suggest a possible involvement of the pathways for synthesis and breakdown of sulfur amino acids via methionine.

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Huating Dou

Postharvest pitting, which has severely affected citrus quality, can be caused by wax application and high temperature storage. Internal volatile composition of waxed and non-waxed fruit could be an indicator of fruit susceptibility to postharvest pitting. In this study, volatile composition was compared between pitted and non-pitted `Fallglo' tangerines [Bower citrus hybrid (citrus reticulata Blanco × C. reticulata Blanco × C. paradisi Macf.) × Temple (C. reticulata Blanco × C. sinensis L.)], as well as in white `Marsh' grapefruit (C. paradisi Macf.). Pitted fruit had a higher volatile concentration than non-pitted `Fallglo' tangerines or white `Marsh' grapefruit. Concentrations of camphene, ethyl hexanoate, alpha-phellandrene, 3-carene, alpha-terpinene, p-cymene, and limonene were higher in pitted white `Marsh' grapefruit than in those of non-pitted fruit. In `Fallglo' tangerines, higher concentrations of limonene and citronellal were found in pitted fruits than in non-pitted fruit. In peel samples of grapefruit, seven different volatiles (methanol, ocimene, citronellyl acetate, alpha-copaene, trans-caryophyllene, alpha-humulene and valencene) were significantly higher in pitted peel than in non-pitted grapefruit peel. Volatiles, such as limonene could be used to predict peel disorders of white `Marsh' grapefruit and `Fallglo' tangerines during storage.

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Jacob B. Bade, Frederick G. Gmitter Jr. and Kim D. Bowman

Volatile oils were extracted from aqueous leaf suspensions of sweet orange [Citrus sinensis (L.) Osb.] cultivars Hamlin, Navel, and Valencia and grapefruit (Citrus paradisi Macf.) cultivars Marsh and Ray Ruby. Pressurized air was used as the sparging gas, and volatile oils were collected in a C-18 cartridge. Gas-liquid chromatography was used to separate and quantify 17 volatile components. Significant quantitative differences for individual components made it possible to distinguish sweet orange from grapefruit (four components), `Marsh' from `Ray Ruby' grapefruit (two components), `Hamlin' from `Valencia' or `Navel' orange (six components), and `Valencia' from `Navel' (three components). The simplicity and sensitivity of the procedure suggest potential use for Citrus taxonomic, genetic, and breeding research.

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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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Yan Wang and Stanley J. Kays

The sweetpotato weevil (SPW) [Cylas formicarius elegantulus (Summers) (Coleoptera: Curculionidae)] is the single most devastating pest of the sweetpotato [Ipomoea batatas (L.) Lam.] worldwide. Attempts to develop host-plant resistance have been only moderately successful due in part to deficiencies in parent and progeny selection methods. Host-plant phytochemicals play critical roles in insect behavior, modulating a cross-section of key behavioral decisions. Thus, identification of the phytochemicals the female weevil uses in decision making could greatly facilitate development of host-plant resistance. The volatile chemistry of the sweetpotato was studied in relation to the host-finding behavior of the female weevil. Critical biologically active volatiles were determined via isolation (Tenax trapping), fractionation (gas chromatography-thermal conductivity detector), identification (gas chromatography and gas chromatography-mass spectroscopy), and bioassay (olfactometry). Differences in volatile chemistry among sweetpotato clones that may relate to differences in resistance or susceptibility to the female SPW were assessed. Volatile extracts from storage roots (site of oviposition) and aerial plant parts were attractive to female SPW, the former being substantially greater. In total, 33 compounds were identified from storage roots and aerial plant parts, including 23 terpenes. Three oxygenated monoterpenes (nerol, Z-citral, and methyl geranate), found in storage roots but not aerial plant parts, were identified as attractants. The sesquiterpene volatile fraction was repellent to female SPW with α-gurjunene, α-humulene, and ylangene active in the concentration range emanating from storage roots. The aerial plant parts emanated a higher composite concentration of sesquiterpenes than storage roots. Differences in the relative attraction among four sweetpotato cultivars to female SPW was inversely correlated with the composite concentration of headspace sesquiterpenes. Selection of clones with decreased volatile attractants and/or increased deterrents using an analytical means of quantification may significantly facilitate developing resistance to the SPW.

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Elizabeth A. Baldwin, Myrna O. Nisperos-Carriedo and Manuel G. Moshonas

Whole tomato fruit (Lycopersicon esculentum Mill.), cvs. Sunny and Solarset, were analyzed at 5 different ripening stages for ethylene and CO2 production. Homogenates from the same fruit were prepared for determination of color, flavor volatiles, sugars and organic acids. Of the flavor volatiles measured, only eugenol decreased during ripening in both varieties and 1-penten-3-one in `Sunny' tomatoes. Ethanol, and trans-2-trans-4-decadienal levels showed no change or fluctuated as the fruit matured while all other volatiles measured (cis-3-hexenol, 2-methyl-3-butanol, vinyl guiacol, acetaldehyde, cis-3-hexenal, trans-2-hexenal, hexanal, acetone, 6-methyl-5-hepten-2-one, geranylacetone and 2-isobutylthiazole) increased in concentration, peaking in the later stages of maturity. Synthesis of some volatile compounds occurred simultaneously with that of climacteric ethylene and color. `Solarset' fruit exhibited higher levels of sugars and all flavor components except ethanol, vinyl guiacol, hexanal and 2-methyl-3-butanol in the red stage. There were no differences between these varieties for acids

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J.P. Mattheis and D.A. Buchanan

Apple fruit storage lie is prolonged by low-oxygen cold storage, however, ethanol accumulates when oxygen concentration is reduced below the Pasteur point, Upon return to aerobic conditions, dissipation of ethanol occurs due to physical (evaporation) and biochemical processes. Oxidation of ethanol by apple fruit occurs at a slow rate, but ethanol also serves es a substrate for fruit volatile synthesis. This study was conducted to determine changes in concentrations of ethanol and other non-ethylene apple fruit volatiles following periods of anaerobiosis. `Delicious' apples were obtained from a commercial warehouse and stored at 0.05% O2, 0.2% CO2 and 1 C. One day following return to ambient oxygen conditions, several volatiles were identified from anaerobic fruit that were nor produced by the control fruit. All were eaters that contained an ethyl group as the alcohol-derived portion, These included ethyl acetate, ethyl butyrate, ethyl 2-methyl butyrate, ethyl hexanoate and ethyl octanoate. Several esters produced by the controls were not detectable from anaerobic fruit including butyl butyrate, butyl 2-methyl butyrate, propyl hexanoate and 3-methyl butyl hexanoate. After 7 days ripening at 20 C, the amount of ethanol and the additional ethylesters was reduced in anaerobic fruit. Synthesis of esters produced by control fruit but nor by anaerobic fruit during the initial volatile sampling had resumed after 7 days.