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Peter H. Dernoeden, John E. Kaminski and Jinmin Fu

single application, and large areas would require overseeding ( Branham et al., 2005 ). In an unpublished Maryland study, however, four summer applications of the ester formulation of triclopyr applied at 1.12 kg·ha −1 a.i. were shown to safely control

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Nobuko Sugimoto, A. Daniel Jones and Randolph Beaudry

Esters are the primary aroma impact compounds produced in ripening apple fruit and normally account for 80% to 95% of the total volatiles emitted ( Paillard, 1990 ). Fresh apples autonomously produce an abundance of hexyl acetate, butyl acetate, and

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David Obenland, Sue Collin, James Sievert and Mary Lu Arpaia

, which identified four esters that were considerably enhanced in amount by this treatment. Of these two, ethyl hexanoate and ethyl butanoate were both present in concentrations well exceeding published aroma thresholds for standards of these compounds in

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Sastry Jayanty, Jun Song, Nicole M. Rubinstein, Andrés Chong and Randolph M. Beaudry

The temporal relationship between changes in ethylene production, respiration, skin color, chlorophyll fluorescence, volatile ester biosynthesis, and expression of ACC oxidase (ACO) and alcohol acyl-CoA transferase (AAT) in ripening banana (Musa L. spp., AAA group, Cavendish subgroup. `Valery') fruit was investigated at 22 °C. Ethylene production rose to a peak a few hours after the onset of its logarithmic phase; the peak in production coincided with maximal ACO expression. The respiratory rise began as ethylene production increased, reaching its maximum ≈30 to 40 hours after ethylene production had peaked. Green skin coloration and photochemical efficiency, as measured by chlorophyll fluorescence, declined simultaneously after the peak in ethylene biosynthesis. Natural ester biosynthesis began 40 to 50 hours after the peak in ethylene biosynthesis, reaching maximal levels 3 to 4 days later. While AAT expression was detected throughout, the maximum level of expression was detected at the onset of natural ester biosynthesis. The synthesis of unsaturated esters began 100 hours after the peak in ethylene and increased with time, suggesting the lipoxygenase pathway be a source of ester substrates late in ripening. Incorporation of exogenously supplied ester precursors (1-butanol, butyric acid, and 3-methyl-1-butanol) in the vapor phase into esters was maturity-dependent. The pattern of induced esters and expression data for AAT suggested that banana fruit have the capacity to synthesize esters over 100 hours before the onset of natural ester biosynthesis. We hypothesize the primary limiting factor in ester biosynthesis before natural production is precursor availability, but, as ester biosynthesis is engaged, the activity of alcohol acyl-CoA transferase the enzyme responsible for ester biosynthesis, exerts a major influence.

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Nihad Alsmairat, Philip Engelgau and Randolph Beaudry

The synthetic and/or catabolic pathways of the amino acids valine, leucine, isoleucine, methionine, phenylalanine, and alanine contribute to the formation of odor-active alcohols, aldehydes, carbonyls, and esters in edible plant parts ( Azevedo et

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J.P. Mattheis, D.A. Buchanan and J.K. Fellman

Quantitative and qualitative changes in net production of volatile compounds by apples occurs during fruit development with a major transition to ester production occurring as fruit ripening begins. Ester production during fruit ripening is an ethylene-mediated response; however, differences in maturation patterns among apple cultivars led us to examine the relationship between ester production and onset of the ethylene climacteric in several commercial apple cultivars. Emission of volatile esters as a function of apple fruit development was evaluated for `Royal Gala', `Bisbee Delicious', `Granny Smith', and `Fuji' apple fruit during two harvest seasons. Apples were harvested weekly and analyses of harvest maturity were performed the day after harvest. Non-ethylene volatiles were collected from intact fruit using dynamic headspace sampling onto Tenax traps. Fruit from each harvest was stored at 1°C in air for 5 months (3 months for `Royal Gala') plus 7 days ripening at 20°C, then apples were evaluated for the development of disorders. The transition to ester production occurred after internal ethylene exceeded 0.1 μL for `Royal Gala', `Bisbee Delicious', and `Fuji'. Ester emission by `Granny Smith' apples remained low throughout the harvest period. Increased ester emission occurred after the optimum harvest date (as determined by the starch index and internal ethylene concentration) for controlled-atmosphere storage of `Bisbee Delicious' and prior to optimum maturity for `Royal Gala' and `Fuji'. A relationship between the potential for development of superficial scald and ester production at harvest was evident only for `Bisbee Delicious' apples.

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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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J. K. Fellman, D. S. Mattinson, James P. Mattheis and D.A. Buchanan

Volatile esters from acids and alcohols are important components of flavor and odor perception in apples (Malus domestica Borkh.). We are interested in understanding the biochemical basis for ester synthesis/flavor retention in `Gala' apples held in controlled atmosphere storage. The relationship between acetyl CoA alcohol transferase (AAT) acetate ester-formin activity, non-ethylene volatile emission, and flesh volatile content of `Gala' apples during the maturation period and after removal from CA storage was investigated. At the appropriate times, apples were sampled for volatile compounds in the headspace and flesh using solid sorbent along with purge-and-trap capillary gas chromatography. Subsequently, acetate ester forming activity was assayed on partially-purified extracts of cortical tissue. During storage, the accumulation of the major flavor notes butyl acetate and 2-methyl butyl acetate in the flesh was decreased as oxygen levels in storage atmospheres were lowered. AAT activity is closely linked to the onset of climacteric ripening and is sensitive to atmospheres having low oxygen contents.

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J.P. Mattheis, D.A. Buchanan and J.K. Fellman

Fruit quality and volatile compounds produced by apple fruit (Malus ×domestica Borkh. `Gala') were characterized following regular atmosphere (RA) or controlled atmosphere (CA) storage at 1°C. Static CA conditions were 1, 1.9, 2.8, or 3.7 kPa O2. Fruit stored under dynamic CA conditions were exposed to ambient air 1, 2, or 3 days per week for 8 hours then returned to 1 kPa O2. All CA treatments included 2 kPa CO2. Ethylene production was reduced following CA storage plus 1 day at 20°C compared with apples stored in RA. Apples stored in static 1 kPa O2 and the dynamic treatments had lower ethylene production compared with apples stored in 1.9 to 3.7 kPa O2 after 90 and 120 days. Ethylene production by apples from all CA treatments recovered during a 7-day poststorage ripening period at 20°C. Ester production was reduced following CA at 1 kPa O2 after 60 days compared with RA-stored fruit. Production of butyl acetate by apples stored in 1 kPa O2 static CA was 29%, 30%, and 7% of that produced by RA-stored fruit after 60, 90, and 120 days storage plus 7 days at 20°C. Amounts of 2-methylbutyl acetate were not affected by CA storage, however, production of other 2-methylbutyrate esters was reduced following 1 kPa O2 storage. Ester production increased with O2 concentration after 90 days in storage. The dynamic treatments resulted in greater ester emission after 120 days storage plus 7 days at 20°C compared with apples stored in static 1 kPa O2. Production of 1-methoxy-(2-propenyl) benzene by apples subjected to dynamic treatments was also higher after 120 days storage plus 7 days at 20°C compared with apples stored in RA or static CA. No differences in firmness, titratable acidity or soluble solids content were observed between apples stored in 1 kPa O2 and the dynamic treatments. Firmness and titratable acidity were maintained better by dynamic treatments compared with static atmospheres containing > 1 kPa O2.

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Dangyang Ke, Lili Zhou and Adel A. Kader

`Chandler' strawberries (Fragaria ananassa Duck.) were kept in air, 0.25% O2, 21% O2 + 50% CO2, or 0.25 O2 + 50% CO2 (balance N2) at 5C for 1 to 7 days to study the effects of controlled atmospheres (CAs) on volatiles and fermentation enzymes. Concentrations of acetaldehyde, ethanol, ethyl acetate, and ethyl butyrate were greatly increased, while concentrations of isopropyl acetate, propyl acetate, and butyl acetate were reduced by the three CA treatments compared to those of air-control fruit. The CA treatments enhanced activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) but slightly decreased activity of alcohol acetyltransferase (AAT). The results indicate that the enhanced PDC and ADH activities by CA treatments cause ethanol accumulation, which in turn drives the biosynthesis of ethyl esters. The increased ethanol concentration also competes with other alcohols for carboxyl groups for esterification reactions. The reduced AAT activity and limited availability of carboxyl groups due to ethanol competition decrease production of other acetate esters.