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John N. Sacalis

It has previously been demonstrated that exceedingly high concentrations of 2,4-D, when taken up by cut carnations, inhibit petal senescence, while application of low concentrations of this synthetic auxin promote petal senescence. The mode of action of such high concentrations of 2,4-D has not been elucidated.

In previous work, it was observed that significant amounts of volatiles always emanated from those flowers treated with high 2,4-D, and which displayed inhibition of ethylene synthesis as well as petal senescence. In the present work, the headspace of treated flowers was therefore tested by gas chromatography after enclosure for a short period of time. Two of the major constituents of the volatiles produced by the treated flowers were found to be ethanol and acetaldehyde.

Since ethanol has formerly been shown to delay senescence in carnation flowers, and since 2,4-D has been shown to induce alcohol dehydrogenase, it is suggested that the mode of action of 2,4-D in this case is by means of the ethanol produced as a result of the 2,4-D treatment.

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Dangyang Ke and Adel A. Kader

Fruits of peach (Prunus persica L., cv. `Fairtime') and plum (Prunus domestica L., cv. `Angeleno') were kept in air and in 0.25% or 0.02% O2 at 0, 5, or 10°C for 3 to 40 days to study the effects of temperatures and insecticidal low O2 atmospheres on their physiological responses and quality attributes. Exposure to low O2 atmospheres reduced respiration and ethylene production rates of the stone fruits. The low O2 treatments retarded color change and flesh softening of plums and maintained acidity of peaches. Exposure to the low O2 atmospheres also delayed incidence and reduced severity of internal breakdown (chilling injury) and decay of the peaches at 5°C and, therefore, maintained both external and internal appearance qualities of the fruits longer than those kept in air. The most important limiting factor for fruit tolerance to insecticidal low O2 atmospheres was development of alcoholic off-flavor which was associated with accumulation of ethanol and acetaldehyde in the fruits. The peaches and plums could tolerate exposures to the low O2 atmospheres for 9 to 40 days, depending on the temperature and O2 level used. These results suggest that stone fruits are quite tolerant to insecticidal low O2 atmospheres.

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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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A.A. Kader, D. Ke, M. Mateos, and E. Yahia

Fruits of `Bartlett' pear (Pyrus communis L.) at green (preclimacteric) and yellow (postclimacteric) stages were kept in 0.25% O2 (balance N2), 80% CO2 (balance O2), or 0.25% O2 + 80% CO2 (balance N2) for 1, 2, or 3 days followed by transfer to air at 20C for 3 days to study the effects of these controlled atmosphere (CA) treatments on anaerobic products and enzymes. All the three CA treatments caused greater accumulation of ethanol, acetaldehyde, and ethyl acetate than the air control. The postclimacteric pears were more sensitive to CA treatments as indicated by occurrence of skin browning, enhanced activity of pyruvate decarboxylase, and higher concentrations of the anaerobic volatiles. For the preclimacteric pears, the 0.25% O2 treatment dramatically increased alcohol dehydrogenase (ADH) activity, which was associated with the induction of one ADH isozyme. Exposure of preclimacteric pears to 80% CO2 slightly increased ADH activity while treatment with 0.25% O2 + 80% CO2 resulted in lower AD11 activity than 0.25% O2 alone.

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Yiping Gong, Peter M.A. Toivonen, O.L. Lau, and Paul A. Wiersma

Apple fruits (Malus domestica Borkh. cv. Braeburn) harvested from two orchards (A and B) on the same day were stored in air or pretreated in air for 0, 2 (2dCA) or 4 weeks (4dCA) before moving into controlled atmosphere (CA) storage with 1.5% O2 + 5% CO2. During storage at 1 °C for 9 weeks in air and/or CA, changes of pyruvate decarboxylase (PDC) activity, alcohol dehydrogenase (ADH) activity, acetaldehyde (AA) and ethanol (EtOH) concentrations in flesh tissue were assayed in addition to the incidence of Braeburn browning disorder (BBD). Immediate introduction to CA conditions induced the development of BBD with the highest incidence 62.2%, however delaying application of CA for 2 and 4 weeks reduced the incidence of BBD to 38.5% and 27.0%. The development of disorder in grower B was less than in grower A. 2dCA and 4dCA treatments did not influence PDC activity compared with treatment of CA. However, ADH activity and the accumulation of AA and EtOH in treatments of 2dCA and 4dCA were markedly lower than those in CA. The accumulation of AA in grower B was lower than grower A. The results of this study suggest that the delayed application of CA reduced BBD and this may be due to reduced anaerobic metabolism of fruits in the delayed CA.

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S.M. Silva and R.M. Beaudry

The generation of dilute vapor phase standards using the static headspace method can be challenging, requiring the construction of specialized chambers or use special methods for adding minute amounts of the compound of interest. The vapor concentration above a dilute water solution can be effective and accurate and has been used to create standards to measure the concentration for a wide range of volatile and semivolatile organic compounds. Such systems are highly temperature-sensitive, however. The goal of this work is to mathematically describe the relationship between vapor concentration above a dilute water mixture for compounds important to postharvest physiology, such as ethanol, acetaldehyde, ethyl acetate, and hexanol. The experiments were carried out in the range of 0 to 40°C and concentration of 0 to 1000 ppm for each compound. Three replications were used for each data point. The concentration was measured after thermal and chemical equilibration by gas chromatography containing a HAYESSEP-N column, by injecting 1 cc of the vapor headspace, using a 8-cm-long needle Hamilton syringe. Relationships for each of the compounds noted were successfully described employing multiple-order equations. For example, the relationship for ethanol vapor concentration was: Y = 12.12356 + 0.9461594*X + 0.5761110e-01*X2 + 0.6565694E-03*X3 + 0.23499598E-04*X4 (R 2 = 1.000), with X being the temperature in °C. The relationships described for those compounds provides an useful tool that allows us to dilute liquid standards across a range of temperatures.

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Yong Seo Park, Clara Pelayo, Betty Hess-Pierce, and Adel A. Kader

`Shinko' and `Shinsui' Asian pears were kept in air, 2 kPa O2, 2 kPa O2 + 2.5 kPa CO2, and 2 kPa O2 + 5 kPa CO2 (balance N2 in each treatment) at 0 °C or 5 °C for up to 24 weeks. The three CA treatments reduced respiration (O2 consumption) and ethylene production rates relative to air control pears; these rates were higher at 5 °C than at 0 °C and higher for `Shinsui' than for `Shinko' pears. While `Shinsui' pears had a climacteric pattern of respiration and ethylene production rates, `Shinko' pears produced very small quantities of ethylene and exhibited a non-climacteric respiratory pattern. `Shinko' pears had a much longer postharvest life than `Shinsui' pears (24 weeks vs. 12 weeks at 0 °C). CA treatments had a greater effect on delaying deterioration of `Shinsui' than `Shinko' pears, which were more sensitive to CO2 injury and associated accumulation of fermentative metabolites (acetaldehyde, ethanol, ethyl acetate). `Shinko' pears did not benefit from CA storage and were best kept in air at 0 °C. An atmosphere of 2 kPa O2 with or without up to 5 kPa CO2 delayed flesh breakdown of `Shinsui' pears during storage 0 °C.

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E.A. Baldwin, T.M.M. Malundo, R. Bender, and J.K. Brecht

Mango fruit, cv. Tommy Atkins, were harvested from two grove sites in south Florida at mature green (MG) and tree ripe (TR) maturities. The fruit were either coated with one of two coatings (NS = Nature Seal® 4000, a polysaccharide coating, or CW = carnauba wax) or left uncoated (control) and stored in humidified air or held in a controlled atmosphere (CA = 5% O2 plus 25% CO2) at 12 °C for 21 days followed by 2 days in air at 20 °C. There were 12 fruit for each treatment/maturity stage combination replicated by grove site. After storage, the pulp was homogenized for later consumer or descriptive panel analysis. Measurements for total soluble solids (SS), pH, titratable acidity (TA), and flavor volatile compounds were also made. TR-harvested fruit were sweeter and generally more aromatic than MG-fruit as determined by sensory and/or chemical analysis. NS-coated fruit were more sour, bitter, and astringent compared to controls and CA-treated fruit. NS-coated fruit received lower overall consumer scores than CW-coated fruit, but were not different from controls or CA-treated fruit. This was reflected also in descriptive panel ratings. There were no differences based on storage treatment for SS, pH, or TA; however, NS-coated fruit were higher in acetaldehyde, methanol and ethanol compared to control or CA-treated fruit. Correlation and regression analysis showed significant relationships between sensory and chemical data.

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Andrés R. Schwember and Kent J. Bradford

Seed priming (controlled hydration followed by drying) is used to alleviate high temperature inhibition of germination and improve seedling emergence of lettuce (Lactuca sativa L.) and other species. However, seed priming can also reduce the longevity of seeds during dry storage. Alternative drying methods [i.e., slow drying or moisture content reduction (MCR) before drying] can extend seed longevity compared to conventional rapid drying procedures after priming. Three postpriming drying treatments were tested on `Conquistador' and `Genecorp Green' lettuce seeds: rapid drying, slow drying and MCR (10% fresh weight loss, then held at 100% relative humidity (RH) for 6 hours, followed by rapid drying). The effects of the postpriming treatments on seed quality and longevity were compared based upon standard germination tests, germination rates, thermogradient table tests, controlled deterioration (CD) tests, and headspace volatiles analysis. The latter may be correlated with seed longevity as release of volatiles (e.g., acetaldehyde, ethanol) is associated with lipid peroxidation. While neither slow drying nor MCR before drying restored lettuce seed longevity to that of the control (not primed) seeds, the MCR method generally gave better results in both cultivars compared to rapid drying. Among the CD test conditions used, 50 °C and 75% RH gave the most consistent results for estimating potential longevity. Headspace volatile emissions from both control and primed lettuce seeds were very low and were not well correlated with seed longevity. Alternative postpriming drying regimes can extend seed longevity while retaining the beneficial effects of priming.

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John C. Beaulieu, Edna Pesis, and Mikal E. Saltveit

An in vitro assay was used to determine the effect of AA and pH on the enzymatic and nonenzymatic production of ethylene (C2H4) from ACC. We were interested in the effect of AA on C2H4 production from ACC because aldehydes, primarily AA, can accumulate in tissue as the result of ripening, storage under modified atmospheres, packaging, and stress. Using crude extracts of ACC oxidase from tomato (Lycopersicon esculentum Mill. `Castlemart') and apple (Malus ×domestica Borkh. `Golden delicious'), C2H4 production from ACC was shown to increase in response to an increase in pH above 7.2 and inclusion of 0.2 to 2 mm AA. Nonenzymatic C2H4 production from ACC also increased linearly with increasing AA concentrations in all the buffers tested. Removal of ascorbate or O2 suppressed AA-induced nonenzymatic C2H4 production. Nonenzymatic AA-induced production of C2H4 from ACC appeared to be an ascorbate dependent oxidation, which was augmented by O2 and was sensitive to minor pH fluctuation. The nonenzymatic AA-stimulated conversion of AEC to 1-butene lacked stereospecificity. Formaldehyde and propionaldehyde also stimulated C2H4 production from ACC. These data indicate that ACC oxidase assays or C2H4 measurements assessing physiological status can be seriously affected by the presence of aldehydes, such as AA. Chemical names used: AA, acetaldehyde; ACC, 1-aminocyclopropane-1-carboxylic acid; AEC, 1-amino-2-ethylcyclopropanecarboxylic acid; ADH, alcohol dehydrogenase; EtOH, ethanol.