Examples from various harvest regimes, storage regimes, cultivars and different packaging methods are presented to characterize volatile ester differences after cutting and how changes occur in characteristic flavors throughout the postharvest life of certain cut fruit products. In many fresh-cut cantaloupe cultivars and in honeydew, there was a relative increase in nonacetates and coinciding relative decrease in acetates during storage. A similar and consistent nonacetate:acetate ester ratio was conserved in cantaloupe from eastern and western U.S. regions, as well as different cultivars from the same field. Furthermore, similar ratios were observed in many melon cultivars over multiple years from different seasons and growing regions. Since many cultivars exhibited similar trends in 2-year repeated studies, the trend is apparently independent of year and season. Fresh-cut `Gala' apples, on the other hand, displayed a slightly different trend whereby both acetates and nonacetate esters decreased appreciably during storage. The hypothesis is put forward that recycling of esters during storage in certain fresh-cut fruits disturbs the delicate fine balance of characteristic volatiles. Consistently decreasing acetates along with increasing nonacetates could alter the overall perceived desirable flavor attributes during fresh-cut melon storage, even though volatile esters are still abundant.
John C. Beaulieu
A likely reason why consumers are not repeat buyers of many fresh-cut fruit is inconsistent or unsatisfactory flavor and/or textural quality. Research toward understanding mechanisms responsible for generation, and/or loss of flavor compounds in fresh-cut fruit is limited. Solid phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) were utilized to study flavor volatile profiles in anthesis-tagged cantaloupe (Cucumis melo L. var. reticulatus Naud. cv. Sol Real) during growth, development, and for fresh-cuts prepared from fruit with five distinctly different harvest maturities. One-quarter-slip fruit had a clearly green, well-attached peduncle; 1/2-slip fruit had a distinct abscission detectable at the peduncle, 3/4-slip fruit were approaching commercial harvest, full-slip (FS) fruit are or will cleanly separate from the vine with light pressure; and over-ripeness (OR) was precisely categorized as 2 days past FS. Recovery of total volatiles displayed a linear response and most volatile classes (except aldehydes) generally followed a trend upon processing where FS > 3/4-slip > 1/2-slip > 1/4-slip. On day 0, only 70.0%, 37.7%, and 20.5% total volatiles were recovered in 3/4-slip, 1/2-slip, and 1/4-slip fruit, compared to FS fruit. During fresh-cut storage, percent total esters followed an increasing linear trend that was maturity-dependent. Percent total aromatics and percent aldehydes followed a linear trend that was maturity-dependent whereby 1/4-slip > 1/2-slip > 3/4-slip > FS. During storage, the relative percentage of acetates decreased, and displayed a maturity-dependent curvilinear trend. The magnitude of the slope decreased with maturity, indicating that the effect of storage time decreased as maturity increased. In FS, 3/4-slip, 1/2-slip, and 1/4-slip cubes, acetates comprised 66.9% of all compounds recovered on day 0 yet, only 26.1% to 44.2%, and 21.3% to 32.6% remained on days 9 and 14, respectively. For all maturities, a curvilinear increase in relative percentage of nonacetate esters was observed during storage. There was a uniform change in the ester balance (nonacetate ester:acetate ratio) during fresh-cut storage, which was independent of initial processing maturity. The overall ester ratio changed roughly 2-fold after just 2 days in optimum storage, and after 5 days it increased more than 3-fold. The shift in endogenous ester compounds could be partially responsible for the apparent loss of characteristic flavor in fresh-cut cantaloupe through long-term storage.
John C. Beaulieu and Mikal E. Saltveit Jr.
Tomato (Lycopersicon esculentum Mill., cv. BHN 91) fruit were hand harvested at the pink sage of maturity and stored at 12.5, 20, and 30C in air, 3% O2 + 5% CO2, or 0.5% O2 + 20% CO2 for up to six days. Half of the fruit were inoculated with Fusarium. Control fruit retained the best appearance in 3% O2 + 5% CO2 at both 20 and 30C. Inoculated fruit at 12.5, 20 and 30C in air or 3% O2 + 5% CO2 were acceptable for 12, 3 and 2 days, respectively, but they deteriorated more rapidly compared to fruit held in 0.5% O2 + 20% CO2 as temperature and time increased. Off-odors were present in all 0.5% O2 + 5% CO2 treatments by days 12, 9 and 5 at 12.5, 20 and 30C, respectively. A significant time- and temperature-dependent increase in pH of locular and pericarp tissue, and of supernatant pH occurred in inoculated regions of fruit held in air by days 12, 6 and 3 at 12.5, 20 and 30C, respectively. In contrast, reduced acidity occurred at 9 and 5 days in 3% O2 + 5% CO2 at 20 and 30C, respectively. Generally, increased pH followed a trend with air > 3% O2 + 5% CO2 > 0.5% O2 + 20% CO2.
John C. Beaulieu and Dyremple B. Marsh
Sweetpotato (Ipomoea batatas) cultivars, Carver, Potojam, Jewel and Centennial were evaluated for slip production, using topsoil, sawdust, sand and a general-purpose peat-based commercial growing media as bed covers. Temperature measured 2 inches (5.1 cm) below the surface of the hot bed varied with covers and date measured. Sand maintained the highest bed temperature, 77 °F (25.0 °C) at 0800 hr and 79 °F (26.1 °C) at 1400 hr, throughout the growing season. Peat-covered roots produced the maximum number of slips/plot (111), while roots covered with topsoil and sawdust produced comparable yields, 55 and 45 slips/plot, respectively. Slip production varied according to harvest date, with the third harvest producing the most slips/plot (83 and 153, in year 1 and year 2, respectively), which, was likely related to increased temperatures. Cultivar significantly influenced number of slips, length of slips, and number of roots per slip. `Potojam' was the most prolific slip producer for both early and mid season production under all bed covers.
John C. Beaulieu and Mikal E. Saltveit Jr.
The content of acetaldehyde (AA) and ethanol (EtOH) increases in ripening climacteric fruit. Application of EtOH inhibits tomato (Lycopersicon esculentum) fruit ripening without affecting subsequent quality, and AA enhances organoleptic quality. AA inhibited ripening of mature-green tomato discs (MGTD) at about 30% conc of EtOH. The relationship between EtOH and AA inhibition of tomato fruit ripening is unclear. The inter-conversion of AA and EtOH is catalyzed by alcohol dehydrogenase (ADH) which is inhibited by 4-methylpyrazole (4-MP). No adverse physiological effects upon ripening were observed in MGTD receiving 20 μL of 4.0 mM 4-MP. Treating MGTD with 0.5 to 4.0 mM 4-MP in concert with AA (≤2.0 μL/g FW) or EtOH (≤8 μL/g FW) was not deleterious to ripening. A rapid, efficient method for the analysis of tissue AA and EtOH was linear (r2 = 0.97) for discs spiked with 0 to 45 μL EtOH. No temporal (0 to 42 h) changes in tissue AA and EtOH were detected in MGTD receiving 2.0 mM 4-MP. MGTD treated with 2.0 mM 4-MP and 8 μL/g FW EtOH had a 360-fold increase in AA after 6 days of ripening, but had no differences on EtOH conc. These conditions maximally inhibited ripening as determined by lycopene content.
John C. Beaulieu and Dyremple B. Marsh
A greenhouse experiment was conducted to examine the relationship between tissue B concentration and dry matter accumulation in broccoli. `Pirate ' was grown in fine silica sand and supplied nutrient solutions containing 0.2, 0.8, 1.4, 2.0, 2.6, 3.2, 3.8, and 4.4 mg·liter-1 B. Plants were sampled for the 5th, 10th, and 15th fully expanded mature leaf, and plant material was collected' for dry matter measurement and boron analysis at each growth stage. The lowest specific leaf weights for the 5th, 10th, and 15th leaves were obtained with the 4.4 mg·liter-1 treatment. At maturity, leaf, petiole stalk, and shoot dry weights were lowest at 4.4 mg·liter-1 B. Treatments supplying less than 3.2 mg· liter-1 B, resulted in a notable decrease in tissue B concentrations from the 5th to the 15th leaf. There was a linear increase' in B concentration in all leaf tissue samples as B treatment increased. At maturity, optimum B concentrations of 531.5, 73.7, 29.8, and 64.6 mg·g-1 were found for the lamina, petiole, stalk, and head, respectively. These concentrations occurred in plants receiving treatment levels of 2.0-3.8 mg·liter-1 B.
John C. Beaulieu and Mikal E. Saltveit
`Castlemart' tomato (Lycopersicon esculentum Mill.) pericarp discs were used to study the physiological effects of acetaldehyde and ethanol on fruit ripening. Short-term exposure of discs from mature-green fruit to acetaldehyde vapors on a fresh mass basis (≤500 μg·g-1) or ethanol vapors (≤3 mg·g-1) promoted ripening, while higher concentrations inhibited ripening. Discs from mature-green fruit absorbed greater amounts of ethanol and produced significantly higher concentrations of acetaldehyde than discs from breaker fruit. Ripening was promoted by ethanol when the discs were unable to retain or produce a certain level of acetaldehyde. Inhibition of ripening by 4 hours of exposure to ethanol (6 mg·g-1) was almost completely abolished by hypobaric treatments (18 kPa for 24 hours). However, acetaldehyde-induced ripening inhibition (2 days exposure to 180 μg·g-1) was only slightly reduced by vacuum. Concentrations of acetaldehyde and ethanol that inhibited ripening reduced C2H4 production, whereas lower concentrations of acetaldehyde and ethanol that promoted ripening increased C2H4 production. Application of 4-methylpyrazole, an alcohol dehydrogenase inhibitor, enhanced acetaldehyde-induced ripening inhibition and reduced ethanol-induced ripening inhibition or promotion at all concentrations of acetaldehyde and ethanol tested. The inhibition or promotion of ripening of excised tomato pericarp discs by ethanol and acetaldehyde depended on initial fruit maturity, applied volatile concentration, and duration of exposure.
John C. Beaulieu and Jeanne M. Lea
Cantaloupe (Cucumis melo L. var. reticulatus Naudin) were evaluated during development and then fresh-cut cubes were stored after preparation from various maturities to track quality changes during storage. Flowers were anthesis tagged one morning in two seasons (years) and developing fruit were harvested weekly at 13, 20, 27 to 28, and 34 to 35 days after anthesis (DAA). Mature fruit were harvested at 37 to 38 DAA with five distinct maturities: 1/4-, 1/2-, 3/4-slip, full-slip (FS), and overripe (OR). Hunter L* and a* color values indicated a change from pale green to light orange that occurred 28 DAA. There were significant decreases in L*, a*, and b* by day 9 in storage (4 °C) as fresh-cut cubes. After 28 DAA, sucrose dramatically increased, and this was positively correlated with increases in both total sugars (r = 0.882, P = 0.084) and percent soluble solids concentration (r = 0.939, P = 0.041). Gradual deterioration occurred during storage, as determined by a uniform subjective quality criterion, which was independent of maturity. There was a negative linear trend in hand-held and instrumental firmness over the length of storage for each maturity level, and the slopes decreased significantly with increasing maturity, indicating the effect of storage duration decreased as harvest maturity increased. There was a significant increasing trend in vitamin C (P = 0.042) during development from 12 through 35 DAA, then losses were greater in fresh-cut cubes prepared from full-slip fruit (65%) than less-mature fruit: 3/4-slip, 50%; 1/2-slip, 48%; 1/4-slip, 40%. The pH of mesocarp tissue dropped to the lowest value (5.25) just before physiological maturity at 27 to 28 DAA, then peaked after harvest (6.51–6.79), and declined somewhat by the end of storage as fresh-cut cubes. In sum, muskmelon fruit used to produce fresh-cut cubes should be harvested ≥1/2-slip to attain optimum physiological quality and consumer acceptability.
John C. Beaulieu, Allison K. Rausch, and Elaine T. Champagne
Fresh-cut melons in many consumer-ready packages are notorious for “wetting” and accumulation of standing juices. These conditions likely create undesirable flavor and aroma changes. We initiated a study to investigate flavor changes in stored fresh-cut cantaloupe. One objective was to optimize solid phase microextraction (SPME) to evaluate organoleptic compounds. Static head-space SPME analyses were performed on fresh-cut cantaloupe cubes (≈2.5 mm, 5 mm, or 2.5 cm), expressed juice, and homogenized slurries. SPME fiber (100 μm PDMS vs. 75 μm Carboxen/PDMS) exposure time (5, 7.5, 10, 12.5, 15, 17.5, 20 min) was evaluated at 40 °C with various head-space: product ratios, plus or minus NaCl to produce typical chromatograms. Fibers were desorbed in an HP5890 GC with a DB-624 or DB-5 column for 45-min runs and an HP6890 GC (DB-5) equipped with a 5973 MS detector for 35-min runs. Albeit qualitative, the best chromatograms were obtained with 7-ml slurries, stirred with NaCl, exposed to a 10 0μm PDMS SPME fiber for 12.5 min. The 100 μm PDMS fiber produced better chromatograms considering the fact that many important flavor volatiles are low-molecular-weight polar esters and alcohols. These conditions were subsequently used to analyze numerous fresh-cut cantaloupe samples stored various times (0 to 9 days). Over 100 peaks were identified, many of which changed through storage and some are suspected as probable agents responsible for undesirable flavor changes. Our analyses are progressing in an attempt to authenticate compounds associated with flavor-related changes in numerous fresh-cut cantaloupe varieties from various growing regions.
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.