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Steven A. Sargent and Jeffrey K. Brecht

Carambolas (Averrhoa carambola L., cv. Arkin) ware harvested at colorbreak (CB) and light green (LG) ripeness stages, commercially packed and cooled. The next day the fruit were treated as: Control (ungassed): CB, LG; Ethylene pretreatment (ETH) @100ppm: LC for 1, 2 or 3 days at 20°C or 25°. After pretreatment the fruit were stored at 5°. After 1, 2, 3, 4 weeks, 10 fruit from each treatment ware removed from storage and placed at 20°. Fruit color and decay were rated daily until 80% of the fruit in each treatment reached the yellow ripeness stage, at which time external color, total soluble solids (TSS), pH and total titratable acidity (TTA) were determined. Carambolas harvested at the LG stage can be ripened to good quality with ETH pretreatment. For two weeks storage at 5°, 2 days ETH are necessary at 20° or 25° to initiate ripening. For three weeks storage, 3 days ETH are required at 20°, and 2 or 3 days ETH are required at 25°. Fruit stored four weeks were of fair quality. LG with slower ripening initiation developed chilling injury during storage; the fastest initiation had the best color but the shortest marketing life. Fruit harvested CB had slightly higher TSS than ETH-treated LG but pH and TTA were similar.

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Marius Huysamer, L. Carl Greve, and John M. Labavitch

Discs from outer pericarp of mature green (MG) and light red (LR) tomatoes were incubated with 13C6-glucose as precursor to cell wall constituents, to determine biosynthetic capacity of the outer 2mm (including cuticle) and adjacent inner 2mm of tissue. Cell wall material was fractionated into pectic and hemicellulosic classes by sequential extraction, and alditol acetates and partially-methylated alditol acetates were prepared. Neutral sugars (NS), glycosidic linkage compositions and incorporation of label were determined by GC-FID and GC-MS. Rhamnose, arabinose and galactose accounted for ca. 90% of both labeled and total NS in the pectic fractions (sugar ratios within ripeness stage were the same for labeled and total NS). Xylose and glucose accounted for ca. 70% of both labeled and total NS in the hemicellulosic fraction (sugar ratios within ripeness stage were different between labeled and total NS). In the crude cell wall, galactose and glucose contents were significantly higher in the inner than in outer tissues for both MG and LR tomatoes. Loss of galactose during ripening was higher from outer tissues. These results show compositional differences between inner and outer tissues, and suggest that ripening-related wall synthesis may give rise to pectic polymers similar in NS composition to existing polysaccharides, and hemicellulosic polymers which may differ in composition.

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Maria Eloisa G. Quintana and Robert E. Paull

Ripe yellow papaya fruit in the markets frequently show green sunken areas called “green islands” (GI). This disorder seems to be caused by mechanical injury in a commercial postharvest handling system. Fruit at different stages of ripeness (5 to 50% yellow) were dropped from different heights (0 to 100 cm) onto a smooth steel plate to try to create GI. The injury sustained was not the same as GI seen in fruit from the handling system. Fruit (10 to 15% yellow) dropped on different grades of sandpaper (220 mesh to 36 mesh) from a height of 10 cm had injury symptoms similar to those seen on fruit from the handling system. These results suggest that abrasion damage was more important than impact damage in papaya fruit. Heating fruit at 48°C for -6 hours or until fruit core temperature (FCT) reached 47.5°C aggravated the severity of GI. Delaying the time of heating from the time of dropping did not significantly lower the severity of GI, except for fruit heated 24 hours after dropping. Waxing fruit alleviated the severity of GI. The results indicate that avoidance of abrasive surfaces such as the plywood walls of field bins is the best approach to avoiding the unsightly GI blemishes on papaya peel.

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Beth Ann A. Workmaster, Jiwan P. Palta, and Michael Wisniewski

Infrared video thermography was used to study formation of ice in leaves, stems, and fruit of cranberry (Vaccinium macrocarpon Ait. `Stevens'). Ice formed on the plant surface at -1 or -2 °C by freezing of a droplet of water containing ice nucleation-active bacteria (Pseudomonas syringae van Hall). Samples were then cooled to a minimum of -8 °C. Observations on the initiation and propagation of ice were recorded. Leaves froze only when ice was present on the abaxial surface. Once initiated, ice propagated to the stem and then readily to other leaves. In both unripe and ripe fruit, ice propagation from the stem to the fruit via the pedicel was not observed. Fruit remained supercooled for up to 1 hour after ice was present in the stem. Fruit could only be nucleated when ice was present at the calyx (distal) end. Red (ripe) berries supercooled to colder temperatures and for longer durations than blush (unripe) berries before an apparent intrinsic nucleation event occurred. These observations provide evidence that leaves are nucleated by ice penetration via stomata. The ability of fruit to supercool appears to be related to the presence of barriers to extrinsic ice propagation at both the pedicel and fruit surface. Stomata at the calyx end of the fruit in the remnant nectary area may provide avenues for extrinsic ice nucleation.

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B. D. Horton

Peach (Prunus persica, L. Batsch) cultivars vary in the percent of marketable stage fruit from a once-over harvest. Maturity stages are difficult to separate. The difficulty might be related to non-uniform ripening characteristics of the fruit. A method was developed to estimate the variability in maturity at 16 coordinates around the peach. Peaches were sampled at 5 maturity stages: 1) about 1/2 final-swell size; 2) 90% final-swell size; 3) and 4) marketable, and 5) soft ripe. Stages were separated by color chips #1 and #2, #3 and #5 (marketable), or #6. Pared flesh firmness was measured with a modified penetrometer plunger (4.47mm diameter tip 11mm long). Force (F) ranged from about 3 to 45 N. Soluble solids (SS) ranged from 10 to 13% from a 1cm3 cylinder adjacent to the puncture made by the penetrometer. Force and SS from five replications of 2 cultivars indicate that the apex and cheeks are the firmest and highest in SS for most stages tested. Reported correlations of F on the cheek with the yellow ground color or sweetness within marketable fruits are negative. However, correlations in this experiment ranged from R2 = 0 to 0.18 for the green to ripe stages.

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P. Perkins-Veazie, J.K. Collins, and J.R. Clark

Blackberry fruit often exhibit an unattractive discoloration following harvest and storage. This redness appears at random on the berry and has been associated with sunburn or high temperature damage, or with fruit harvested less than fully ripe. We began a study to separate and identify causes of red drupe. Black (fully ripe) berries, free of sunburn, of six blackberry cultivars were harvested in the morning and subjected to conditioning treatments of 20 hours at 2 or at 20°C, followed by 7 days storage at 2°C. Strong cultivar differences and effects of conditioning treatment were found. `Navaho', `Arapaho' and `Chester' had little or no red drupe, regardless of conditioning treatment. As much as 50% of `Shawnee' and `Choctaw' berries exhibited red drupe, with more appearing in fruit conditioned at 2°C. Development of red drupe in berries conditioned at 2°C was quadratically related to total anthocyanin and juice pH, while that of fruit conditioned at 20°C was quadratically related to percent titratable acidity. The red drupe disorder in blackberries is exacerbated by low temperature storage and may be due to decreased cellular pH and subsequent anthocyanin glycosylation in individual drupelets.

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Juan C. Diaz-Perez, S. Bautista, M. Arenas, S. Evangelista, and R. Arce

There are very few postharvest studies about the mamey sapote fruits. The lack of appropriate harvest indexes for this crop result in fruits having a wide variability in maturity after harvest. Fruit skin shows no apparent changes in color as maturity progresses. Another complication results from harvesting the fruit with long poles, which restricts the harvester from touching the fruit to evaluate fruit softening. The objective of this study was to evaluate the effect of exogenous ethylene applications to fruits on increasing the uniformity of fruit maturity. Fruits were harvested every 2 weeks over a 4-month period. Fruit harvest was initiated 8 weeks before the estimated ripening day. Fruits were treated by immersion for 1 min in an ethephon solution at 0, 500, or 1000 mg·liter–1 and stored at 20°C (65% RH) for 4 or 8 days. After the storage period, fruits were analyzed for fruit firmness, color (external and internal), pH, titratable acidity, soluble solids content, ascorbic acid, and starch. Postharvest exogenous applications of ethylene stimulated postharvest ripening of the mamey sapote fruits. Ripening was associated to fruit softening, a change in pulp color from a pale pink to an intense pink color, and an increase in SSC. Fruit response to exogenous ethylene applications was small in immature fruits and increased as fruits approached the ripe stage, and decreased again in over-ripe fruits. In conclusion, postharvest applications of ethylene increased both fruit earliness and maturity uniformity in fruits.

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Dangyang Ke and Adel A. Kader

Selected cultivars of several fruit species were exposed to 0.25% or 0.02% O2 at 0, 5, or 10C for short durations to investigate the potential of these treatments as quarantine procedures for postharvest insect control. Beneficial effects of such low O2 treatments included inhibition or delay of ripening processes as indicated by reduction in respiration and ethylene production rates, retardation of skin color changes and flesh softening, and maintenance of titratable acidity. While appearance was not adversely influenced by the short-term low O2 treatments, the development of alcoholic off-flavor was the most important detrimental effect, which limited the tolerance of fresh fruits to low-O2 atmospheres. Ethanol content and flavor score of the fruits had a logarithmic relationship. The threshold ethanol concentration associated with off-flavor detection (EO) increased with SSC of the commodity at the ripe stage, and it could be estimated using the following formula (Log EO)/SSC = 0.228. Using SSC of ripe fruits and average ethanol accumulation rate per day (V) from each low O2 treatment, the tolerance limit (Tl) of fruits to low O atmospheres could be predicted as follows: Tl = EO/E = 1 00.228 SSC2/V.E

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Marisa M. Wall, Cynthia A. Waddell, and Paul W. Bosland

The β-carotene and total carotenoid content of either fresh or dried tissue of fruits of a total of 57 cultivars of six Capsicum species were analyzed using high performance liquid chromatography (HPLC). β-Carotene levels in ripe fruit varied from 0 to 166 μg·g-1 fresh weight, and carotenoid levels were from 1 to 896 μg·g-1 in ripe fruit in 1996. The range of values for β-carotene was similar in 1997, but that for total carotenoids was wider (4 to 1173 μg·g-1 fresh weight). Fresh fruit of the cultivars Greenleaf Tabasco, Pulla, Guajillo, NuMex Conquistador, Ring-O-Fire, and Thai Dragon contained greater amounts of β-carotene per 100 g fresh weight than the recommended dietary allowance (RDA) for vitamin A for the average adult. For dried Capsicum entries, New Mexican, aji, pasilla, and ancho types had the highest levels of β-carotene. In 1996, β-carotene levels among the dried Capsicum germplasm ranged from 2 to 739 μg·g-1 dry weight, and carotenoid levels from 111 to 6226 μg·g-1. Values were higher in 1997, ranging from 24 to 1198 μg·g-1 dry weight for β-carotene and from 187 to 10,121 μg·g-1 for total carotenoids. A pasilla type (C. annuum L.) had the highest total carotenoid content among the dried entries in both years.

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D.I. Leskovar, P. Perkins-Veazie, and A. Meiri

Water conservation strategies are being investigated for watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] production in the Winter Garden region of southwest Texas. Our objective was to determine how yield and fruit quality of a triploid (cv. Summer Sweet 5244) and hybrid (cv. Summer Flavor 710) watermelon were affected by irrigation based on evapotranspiration (ET) rates and timing of application during spring. Irrigation treatments included constant 1.0 and 0.5 ET, three with varying ET before or after fruit set, and one with cycles of 1.0 and 0.5 ET. Fruit quality characteristics were measured at the unripe, ripe, and overripe maturity stages. Water deficit before or after fruit set decreased yield and fruit number. Flesh color was not affected by irrigation at any maturity stage. Soluble solid content at the ripe stage increased only in triploids irrigated with constant 0.5 ET or with 0.5 ET applied after fruit set. Triploid plants exposed to frequent cycles of water deficit set more and smaller fruit than hybrids. These data suggest that triploid watermelon types may have a different acclimation response to drought stress than diploid hybrids.