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Artur Miszczak, Charles F. Forney and Robert K. Prange

`Kent' strawberries were harvested at red, pink, and white stages of development, and stored at 15C in the light. Fruit were sampled over a 10-day period and evaluated for volatile production and surface color. Volatile production by red and pink fruit peaked after 4 days of storage. Maximum volatile production by red fruit was 8- and 25-fold greater than maximum production by pink and white fruit, respectively. Aroma volatiles were not detected in the headspace over white berries until 4 days following harvest after which volatile production increased through the tenth day of storage. Changes in the surface color of white berries during postharvest ripening coincided with the production of volatiles. In another experiment, red, pink, and white `Kent' strawberries were stored for 3 days at 10 or 20C in the dark or light. Fruit were then evaluated for volatile production, weight loss, anthocyanin content, and surface color changes. White berries produced volatile esters after 3 days of storage at 20C in the light. Both light and temperature influenced the relative production of the volatiles produced by pink fruit. Fresh weight loss, color change, and anthocyanin content were temperature and light dependent.

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Alejandra Ferenczi, Jun Song, Meisheng Tian, Konstantinos Vlachonasios, David Dilley and Randolph Beaudry

The effect of 1-methylcyclopropene (1-MCP) on biosynthesis of volatiles and fruit ripening in apple (Malus ×domestica Borkh.) was investigated using `Golden Delicious', `Jonagold', and `Redchief Delicious' fruit. Application of 1-MCP to `Golden Delicious' at the preclimacteric stage effectively inhibited ripening as determined by decreased expression of genes for 1-amino-1-cyclopropane carboxylic acid (ACC) oxidase (ACO), and ACC synthase, ACO protein content, climacteric ethylene production, respiration, and volatile ester biosynthesis. Exogenous ethylene applied after 1-MCP treatment did not induce ethylene production, respiration, or volatile production. Activity for alcohol acyltransferase, which catalyzes the final step in ester formation, was demonstrable for 1-MCP-treated fruit, indicating no strict limitation on ester formation is imposed by this enzyme and that ester formation in 1-MCP-treated apple fruit is at least partially limited by reduced substrate synthesis. Once volatile ester formation had been suppressed by 1-MCP, the recovery of volatile synthesis required ≈3 weeks for `Jonagold' and 4 weeks for `Delicious' when held in air at 22 °C. For the first 2 months of storage at 0 °C in air, `Jonagold' and `Delicious' required ≈3 weeks holding at 22 °C for volatile biosynthesis to initiate; after 5 months in refrigerated storage, volatile formation was evident at the time of removal from cold storage. For `Jonagold' fruit held in controlled atmosphere (CA) storage for 2, 5, and 7 months at 0 °C, at least 3 weeks holding at 22 °C were required for volatile formation to begin to recover. The maximal amount of volatile formation was reduced 50% by 1-MCP relative to nontreated control fruit. CA storage had a similar impact on maximal volatile formation. The marketing of 1-MCP-treated fruit soon after treatment might result in the delivery of fruit to the consumer with little likelihood of recovery of volatile ester formation prior to consumption.

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John K. Fellman and James P. Mattheis

Developments in analytical technology, most notably high resolution fused silica open tubular (FSOT) gas chromatography-mass spectromety (GC-MS), make it possible to investigate physiological roles of volatile molecules occurring at low (ppb-ppm) concentrations. Use of headspace and purge-and-trap sampling coupled with cryofocusing injection techniques minimizes artifacts often created when more traditional methods of volatile molecule extraction are used. A challenging aspect of the work is development of appropriate delivery methods for internal standard quantitation of the molecules of interest. Apparently, biosynthesis of certain volatile substances is O2 dependent and others are manufactured in response to a changing environment. FSOT GC-MS investigation revealed dramatic changes in content and quantity of `Bisbee' apple headspace and purgable flesh volatiles during a 5-week harvest maturity period and 4 months of subsequent refrigerated storage. Other studies with apple mesocarp cultures and other fruits show interesting volatile molecule profiles in response to different treatments.

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Rufino Perez, John Linz, Matt Rasick and Randolph M. Beaudry

Minimally processed fruits and vegetables, by virtue of cell disruption resulting from processing and handling, can encourage the growth of microorganisms. There is potential for identification of microorganisms and characterization of microbial products and constituents in food, based on volatile profile analysis. We have prepared a flow-through system to grow several bacteria including E. coli 25922-ATCC and E. coli 0157:H7 and monitored the volatile profiles under conditions similar to those experienced by minimally processed fruits and vegetables during marketing conditions. Specific volatiles have been identified that may have potential to serve as signature-type volatiles in accurate automated quality control systems. For example, indole and a number of short-chain fatty acids are produced in copious amount by E. coli 25922-ATCC, but are not constituent of broccoli or carrot aroma profiles. The data suggest that specific volatiles may serve as “markers” for bacterial presence.

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Zimian Niu*, Dapeng Zhang, Hongyu Zhao and Curt Rom

The volatile aromas from the fruits of `Naganofuji No.2' apple (Malus domestica Mill.) were determined by gas chromatography (GC) and combined GC-mass spectrometry (GC-MS) after different temperature conditions. The fruits from CA storage were sealed in glass and the volatiles in the headspace were determined. Eleven compounds of four chemical classes from active carbon absorbed samples were measured and three of them—tormic acid pentyl ester, butanoic acid-1-methyl ethylester and 4-hydroxy-3-methyl-2-butanone, were identified at 20 °C, but not at °C. Under 20 °C condition, the contents of three volatiles increased from 1 hour and reached to their peaks at the 4th to 7th hour. The content of ethylene reached its peak at 4 hours and changed synchronically with the other volatiles during the experiment. The content of ethylene was significantly positively correlated with the contents of volatile aromas (r = 0.96-0.98, P ≤ 0.01). Under °C condition, the content of ethylene was significant lower than that of at 20°C and there was no ethylene peak produced during experiment. When the fruits were treated with ethephon (0.1 mg·L-1) at 5°C, the content of ethylene increased greatly. The highest level of ethylene was found at 4 to 7 hours and the peaks of volatiles also appeared at 7 hours or 10 hours after the treatment. It was suggested that the production of ethylene in fruits could be thought as an indicator of some volatile aromas.

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Ming Zhang and Eric E. Roos

All kinds of plant seeds evolve volatile compounds during storage. However, a reliable deterioration forecast method is still not established using volatile evolution, even though some preliminary work indicated a relationship between volatile evolution and seed deterioration (Fielding and Goldsworthy, 1982; Hailstones and Smith, 1989; Zhang et al., 1993). Here we review some of the previous work concerning seed volatiles and present some more recent research on the effects of seed moisture content on deterioration. We found that volatile evolution from seeds was controlled by seed moisture level. Generally, seeds tended to evolve more hexanal and pentanal under extremely dry conditions (below 25% equilibrium RH). The production of hexanal and pentanal decreased with increasing seed moisture level. On the other hand, methanol and ethanol increased with increasing seed moisture. All of the volatile compounds accumulated in the headspace of the seed storage container during storage. Therefore, it should be possible to use different volatiles to indicate the deterioration of seeds stored under different moisture levels. We suggest that hexanal may be used for seed assessing deterioration under dry storage conditions (below 25% equilibrium RH), while ethanol may be used for seeds stored under higher moisture conditions (above 25% equilibrium RH). [References: Fielding, J.L. and Goldsworthy, A. (1982) Seed Sci. Technol. 10: 277–282. Hailstones, M.D. and Smith, M.T. (1989) Seed Sci. Technol. 17: 649–658. Zhang et al. (1993) Seed Sci. Technol. 21:359–373.]

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Charles F. Forney and Michael A. Jordan

`Annapolis', `Cavendish', `Honeoye', `Kent', and `Micmac' strawberry fruit (Fragaria ×ananassa Duch.) were harvested underripe (75% to 90% red) or fully ripe. Fruit were stored at 0C for 5 days followed by 2 days at 15C. Volatiles were trapped onto Tenax-GR from the headspace over fruit before and after storage and analyzed using GC-MS. Volatile esters identified in headspace included methyl and ethyl butanoate, methyl and ethyl hexanoate, methyl and ethyl 3-methylbutanoate, 3-methylbutyl acetate, hexyl acetate, and methyl 2-methylbutanoate. Headspace concentrations of volatile esters over freshly harvested strawberries averaged 1.3 and 6.8 μmol·m–3 for underripe and ripe fruit, respectively. After 7 days of storage, volatile concentrations increased in both underripe and ripe fruit to 6.3 and 12.2 μmol·m–3, respectively. There were quantitative and qualitative differences between cultivars. Total volatile concentrations were 16.0, 8.1, 5.7, 2.4, and 0.9 μmol·m–3 in the headspace over `Annapolis', `Kent', `Micmac', `Cavendish', and `Honeoye', respectively. `Annapolis' had the highest concentrations of methyl and ethyl butanoate, while `Micmac' had the highest concentrations of methyl and ethyl hexanoate. Volatile concentrations at harvest increased 5.7, 1.9, 1.7, 1.4, and 1.3 times during storage in `Kent', `Annapolis', `Micmac', `Cavendish', and `Honeoye', respectively. Results indicate that strawberry fruit continue to produce aroma volatiles after harvest.

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Harmander Pal Singh*, Dennis P. Murr, Gopi Paliyath and Jennifer R. DeEll

`Gala' apples (Malus × domestica Borkh) were harvested at optimum maturity for long-term storage, precooled overnight at 0 °C, treated with 1 μL·L-1; 1-methylcyclopropene (1-MCP) for 24 hours at 0 °C, and then placed in controlled atmosphere (CA) to determine the storage regime that would have the least negative impact on post-storage aroma volatile production. Fruit were stored at 0° and 2.5° C in ultra low oxygen (0.6% O2 -0.6% CO2; ULOCA), low oxygen (1.2% O2 -1.2% CO2; LOCA) and standard (2.5% O2 -2.5% CO2; SCA) CA for 120 and 240 days, and in ambient air for 60, 90, 120 and 150 days. Post-storage fruit volatiles were quantified by headspace analysis using a solid-phase micro-extraction (SPME) probe and FID-GC, and key volatiles were identified by GC-MS. Fruit volatile production was greatest at harvest, and decreased thereafter for fruit held in air and CA for up to 150 or 240 days, respectively. 1-MCP treatment resulted in reduced rates of respiration, ethylene and volatile production, regardless of storage regime, and resulted in a reduced production rate of all the major volatile compounds, including esters, alcohols, acids, aldehydes and ketones. Post-storage volatile production was the least in fruits removed from 0 °C in ULO, followed by LO, SCA, and then air. 1-MCP treatment inhibited post-storage volatile production in CA- and air-stored fruit by as much as 95 percent. However, recovery of aroma was delayed significantly in fruit which had been held at 0 °C vs. 2.5 ° C, suggesting aroma volatile synthesis in `Gala' is chilling sensitive.

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Elizabeth A. Baldwin and Myrna O. Nisperos-Carriedo

Edible lipid and composite films were tested for their ability to retain flavor volatiles in `Pineapple' orange fruits stored at 21° using a headspace analysis technique. Volatiles, considered to be important to fresh orange flavor, were quantified and acetaldehyde, ethyl acetate, ethyl butyrate and methyl butyrate increased progressively during storage in coated fruits. Acetaldehyde increased by the second day of storage in uncoated fruits but declined thereafter, `Sunny' tomato fruits were harvested at the green or breaker stage of maturity and ripened at 32.5, 21.0 and 12.9°C. Some fruit from the higher and lower storage temperatures were moved to 21° after one week. In most cases major or important flavor volatiles were highest in fruit transferred to or continuously stored at 21.0°C followed by 12.9 and 32.5°C. Fruit harvested at the breaker stage generally had higher volatile levels compared to those harvested green.

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Elizabeth A. Baldwin and Myrna O. Nisperos-Carriedo

Edible lipid and composite films were tested for their ability to retain flavor volatiles in `Pineapple' orange fruits stored at 21° using a headspace analysis technique. Volatiles, considered to be important to fresh orange flavor, were quantified and acetaldehyde, ethyl acetate, ethyl butyrate and methyl butyrate increased progressively during storage in coated fruits. Acetaldehyde increased by the second day of storage in uncoated fruits but declined thereafter, `Sunny' tomato fruits were harvested at the green or breaker stage of maturity and ripened at 32.5, 21.0 and 12.9°C. Some fruit from the higher and lower storage temperatures were moved to 21° after one week. In most cases major or important flavor volatiles were highest in fruit transferred to or continuously stored at 21.0°C followed by 12.9 and 32.5°C. Fruit harvested at the breaker stage generally had higher volatile levels compared to those harvested green.