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  • Author or Editor: Stanley J. Kays x
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While we tend to think of postharvest volatiles as nitrogen, oxygen, carbon dioxide and ethylene, harvested products are actually exposed to thousands of volatile compounds. These volatiles are derived from both organic and inorganic sources, evolving from storage room walls, insulation, wrapping materials, combusted products, plants, animals, and a myriad of other sources. Plants alone manufacture a diverse array of secondary metabolizes (estimated to be as many as 400,000) of which many display some degree of volatility. We tend to be cognizant of volatiles when they represent distinct odors. A number of volatiles, however, have significant biological activity, and under appropriate conditions may effect postharvest quality. An overview of biologically active volatile compounds and their relation to postharvest quality will be presented.

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Jerusalem artichokes are one of a small number of crops that store carbon predominately in the form of inulin, a straight chain fructosan. There has been a tremendous increase in interest in inulin due to its dietary health benefits for humans and calorie replacement potential in processed foods. We measured the allocation of dry matter within the crop (cv. Sunckoke) during an entire growth cycle by harvesting plants over a 40-week period (2-week intervals) from initial planting through field storage. Plant characters assessed were: no. of basal stems, leaves, branches, flowers, and tubers; the dry weight of leaves, branches, flowers, tubers, and fibrous roots; and date of flowering. Total dry weight of above-ground plant parts increased until 18 weeks after planting (22 Aug.) and then progressively decreased thereafter. Tuber dry weight began to increase rapidly ≈4 weeks (19 Sept.) after the peak in above-ground dry weight, suggesting that dry matter within the aerial portion of the plant was being recycled into the storage organs. Tuber dry weight continued to increase during the latter part of the growing season, even after the first frost. Final tuber yield was 13.6 MT of dry matter/ha.

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The sweetpotato, unlike most vegetable crops, exhibits a vining growth habit where vertical development is sacrificed for rapid radial expansion. Considerable genetic diversity is present in vine length within the sweetpotato genepool. To test the relationship between the degree of vining (land area covered during the growing season) and yield, 5 vine length types (dwarf, bunch, normal, long and very long) were grafted on the same root stock (`Jewel'). At harvest, canopy diameter and area, root fwt and number, total vine length, and number of vines, leaves, missing leaves, nodes and flowers were determined as well as root, vine, leaf, petiole and flower dwt. Individual parameters were related to storage root development and harvest index. Total vine length ranged from 5.0m to 73.8m/plant, while vine number varied from 12.6 to 117.8 vines/plant. The total number of leaves/plant varied from 595 to 2680 while the percent leaf loss ranged from 17 to 38%. Root yield (fwt) was lowest for the dwarf vine type (593 g/plant) alnd highest for the longest vine type (2716 g/plant).

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Abstract

Ethylene-induced abscission of pepper (Capsicum frutescens L. cv. Hungarian Hot Yellow Wax) flower buds, leaves, and fruit depended on ethylene source (i.e. ethylene gas from a compressed gas source vs. ethylene released from Silaid) and concentration. In response to ethylene from either source, flower buds and small fruit (< 10 mm long) abscised most readily and fully expanded leaves least readily. Concentrations of Silaid that induced fruit abscission comparable to a given concentration of ethylene gas induced significantly greater leaf abscission than ethylene gas. Application of Silaid at dusk resulted in a small, but significant, increase in abscission relative to early morning application. Progressive increases in temperature between 18° and 32°C enhanced fruit and leaf abscission in response to ethylene gas. Abscission mediated by ethylene gas was not affected by light intensities between 120 and 300 µmol·m–2·s–1 PAR. Chemical name used: (2-chloroethyl)methylbis(phenyImethoxy)silane (Silaid, CGA-15281).

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The sweetpotato weevil is the single most critical insect pest of the sweetpotato worldwide. While male weevils can be lured to traps using a synthetic female pheromone, crop losses are not adequately reduced since damage is caused by the larvae arrising from eggs laid by female weevils in the storage roots. Identification of a female attractant could greatly enhance the control of the insect. The leaves and storage roots are known to emit volatiles that attract the female and in the following tests, we demonstrate that feeding by female weevils stimulates the synthesis of a volatile attractant which attracts additional females to the root. Undamaged, artificially damaged, and female weevil feeding damaged periderm were tested in dual-choice and no-choice olfactometers. Volatiles from feeding damaged roots were significantly more attractive than undamaged and artificially damaged roots. To test whether the volatile attractant was of weevil or root origin, volatiles were collected in MeCl2 after removal of the weevils and fractionated on a megabore DB-1 capillary column using a GC fitted with a TC detector. Fractions were collected from the exit port and their activity index (AI) determined using dual choice and no choice olfactometry. The active fraction was ascertained and active components identified via GC-MS.

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Using the sweetpotato as a model, we identified precursors of critical flavor volatiles by fractionating, based upon solubility, raw roots into major groups of constituents. Volatile thermophyllic products from the individual fractions were analyized and compared to those from non-extracted root material. Volatile components were seperated and identified using GC-MS and quantified using internal standard methodology. Mechanisms of synthesis of flavor volatiles via thermophyllic reactions will be discussed, as will postharvest treatments that can modulate eventual aromatic properties of cooked plant products.

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Increased interest in the Jerusalem artichoke (Helianthus tuberosus L.) stems from the high level of inulin, a straight chain fructan, found in the tubers that has a number of current and potential industrial applications. Deficiencies in existing cultivars have underscored the need for a pragmatic breeding program. Since synchronization of flowering has a pronounced influence on genetic crosses that can be made, we assessed the flowering date and duration of 190 clones with selected clones similarly monitored for two additional growing seasons. Substantial genetic variation in the date and the duration of flowering were found with the onset of flowering ranging from 69 to 174 days after planting (DAP). Flowering duration ranged from 21 to 126 days. The onset of flowering was substantially affected by planting date and to a lesser extent by location. The results suggest that at lower latitudes flowering date for some clones can be manipulated by planting date; at higher latitudes, growth under controlled conditions may be required to synchronize flowering of some clones.

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Abstract

Ethylene was produced by the Chinese chestnut fruit (Castanea moltissima Blume), its rate increasing substantially prior to dehiscence. The primary site of synthesis was the involucre, rather than the seeds. Elevated levels (2 to 4 μl/kg-hr) of ethylene production by the involucre corresponded with increased respiratory activity; however, the rate of ethylene synthesis declined earlier in the senescence of the involucre than did the CO2 production. Exogenous application of ethylene either as a gas or as (2-chloroethyl)phosphonic acid (ethephon) accelerated the rate at which dehiscence occurred and improved the uniformity of dehiscence among seedling fruits.

Open Access