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- Author or Editor: Stanley J. Kays x
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.
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.
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.
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.
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.
Abstract
Sweet potato plants, Ipomoea batatas (L.) Lam. cv. Porto Rico Red with the storage root production zone subjected to 2.5% oxygen for 81 days, showed an almost complete repression in storage root number and weight, when compared to plants subjected to 21% oxygen. When plants were grown in 2.5% oxygen for 81 days followed by 21% oxygen for 28 days, there was no difference in storage root number when compared to plants grown in 21 % oxygen for the entire period. Alteration of the storage root zone oxygen concentration appears to provide an excellent method for studying the initial biochemical changes occurring during storage root induction and/or development.
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).
Flavor quality is one of the most difficult traits to select in plant breeding programs due to the large number of sensory panelists required, the small number of samples that can be evaluated per day, and the subjectivity of the results. Using sweetpotato [Ipomoea batatas (L.) Lam.] as a model, clones exhibiting distinctly different flavors were analyzed for sugars, nonvolatile acids, and aroma chemistry to identify the critical flavor components. Differences in sugars, sucrose equivalents, nonvolatile acids, and 19 odor-active compounds were identified that accounted for differences in flavor among the clones. Using the intensity of the aroma per microliter for each of the 17 most important aroma-active compounds (maltol, 5-methyl-2-furfural, 2-acetyl furan, 3-furaldehyde, 2-furmethanol, benzaldehyde, phenylacetaldehyde, β-ionone, 1,2,4-trimethyl benzene, 2-pentyl furan, 2,4-decadienal, 2,4-nonadienal, linalool, geraniol, cyperene, α-copane and a sesquiterpene) and the relative sweetness of individual sugars × their respective concentrations, multivariate (principal component and cluster) analysis allowed accurate classification of the clones according to flavor type without sensory analysis. The level of precision was such that sweetness, starch hydrolysis potential, and the concentration of β-carotene could be accurately predicted by quantifying specific volatiles. Analytical assessment of flavor would greatly facilitate the accurate evaluation of large numbers of progeny, the simultaneous selection of multiple flavor types, and the development of superior new cultivars for a wide cross-section of food crops.