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Roisin McGarry, Jocelyn A. Ozga, and Dennis M. Reinecke

Field experiments were conducted on two cultivars of saskatoon to test the effectiveness of ethephon in stimulating uniform fruit ripening without compromising fruit quality. Shrubs of cultivars Northline and Smoky were sprayed to runoff with ethephon (0, 250, 500, and 1000 mg·L-1 for `Northline'; 0, 500, and 1000 mg·L-1 for `Smoky') prior to fruit maturity. Fruit were harvested 4 to 8 days after treatment and sorted into ripeness categories by size, and the fully ripe fruit were evaluated for quality (surface color, firmness, mean fruit weight, soluble solids, and titratable acids). Ethephon significantly increased the percent ripe fruit per shrub (by up to 9.7%) in both cultivars, without a significant effect on fruit quality. At concentrations up to 1000 mg·L-1, ethephon may be an effective ripening agent for saskatoon fruit without reducing fruit quality. Although there were significant differences in yield from year to year for both cultivars because of their biennial-bearing habit, ethephon treatments did not significantly affect total yields.

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Nazir A. Mir, Najma Khan, and Randolf M. Beaudry

The effects of 1-MCP on ripening and shelf life in fruit of five classes of maturity (1, mature green; 2, turning; 3, half-ripe; 4, ripe; and 5, over-ripe) of `Plum' tomato (Lycopersicon × esculentum, Mill) at 22 °C were evaluated. 1-Methylcylopropene (1-MCP) reduced the rate of red color development in fruit of all maturity classes. However, the effect was more discernable in fruit with higher hue angle value. Single application of 1-MCP delayed the color development by 10 days. While a second application of 1-MCP at day 10 delayed color development by another 10 days for mature green tomatoes, it did not influence the color change in all other classes of maturity. The effects of 1-MCP on firmness loss were similar to color development. Compared to the control, 1-MCP reduced the ripening-related rate of respiration by approximately 40%. Contrary to this, ethylene production was not affected by 1-MCP application. Potential exists to use 1-MCP in tomato to reduce ethylene-associated changes in texture and color.

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Charles F. Forney and Michael A. Jordan

`Annapolis', `Cavendish', `Honeoye', `Kent', and `Micmac' strawberry fruit (Fragaria ×ananassa Duch.) were harvested underripe (75% to 90% red) or fully ripe. Fruit were stored at 0C for 5 days followed by 2 days at 15C. Volatiles were trapped onto Tenax-GR from the headspace over fruit before and after storage and analyzed using GC-MS. Volatile esters identified in headspace included methyl and ethyl butanoate, methyl and ethyl hexanoate, methyl and ethyl 3-methylbutanoate, 3-methylbutyl acetate, hexyl acetate, and methyl 2-methylbutanoate. Headspace concentrations of volatile esters over freshly harvested strawberries averaged 1.3 and 6.8 μmol·m–3 for underripe and ripe fruit, respectively. After 7 days of storage, volatile concentrations increased in both underripe and ripe fruit to 6.3 and 12.2 μmol·m–3, respectively. There were quantitative and qualitative differences between cultivars. Total volatile concentrations were 16.0, 8.1, 5.7, 2.4, and 0.9 μmol·m–3 in the headspace over `Annapolis', `Kent', `Micmac', `Cavendish', and `Honeoye', respectively. `Annapolis' had the highest concentrations of methyl and ethyl butanoate, while `Micmac' had the highest concentrations of methyl and ethyl hexanoate. Volatile concentrations at harvest increased 5.7, 1.9, 1.7, 1.4, and 1.3 times during storage in `Kent', `Annapolis', `Micmac', `Cavendish', and `Honeoye', respectively. Results indicate that strawberry fruit continue to produce aroma volatiles after harvest.

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P. Perkins-Veazie, J. K. Collins, and B Cartwright

To determine whether ethylene production was related to locular tissue breakdown in watermelon, plugs from ripe `Jubilee', `Black Diamond', `Tiger Baby', `Mirage', and `King of Hearts' were taken from the skin (epidermis and hypoderm), rind (hypoderm and mesocarp), and placenta (locular and heart) tissues. ACC oxidase activity was <0.05 nmol·g–1·h–1 in locule and heart locations for all cultivars. Skin tissue had the highest activity, ranging from 0. 1 8 for `Jubilee' to 0.5 to 0.62 nmol·g–1·h–1 for the other four cultivars. ACC (1-aminocyclopropane-1-carboxylic acid) and ACC oxidase activity were measured in unripe, ripe, and overripe `Jubilee' melons. ACC oxidase activity from skin tissue was lowest in unripe (0.05 nmol·g–1·h–1) and highest in overripe (0.13 nmol·g–1·h–1) melons, and was 0.05 nmol·g–1·h–1 or less in all other tissues. Free ACC was highest in the skin tissue (1.3 nmol·g–1·h–1), but there was no difference in ACC content with stage of ripeness for any tissue. Results indicate that ethylene may be transported from the outer skin and rind tissues to locular areas and that wounding of the skin tissue could lead to deleterious ethylene production.

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R.E. McDonald, T.G. McCollum, and E.A. Baldwin

Mature green `Sunbeam' tomato fruit (Lycopersicon esculentum Mill.), were treated in varying order with C2H4, 42°C water for 60 minutes, 38°C air for 48 hours, partial ripening for 48 hours at 20°C, or not treated, and then stored at 2°C for 14 days before ripening at 20°C. Heat treated fruit stored at 2°C and transferred to 20°C ripened normally while 63% of nonheated fruit decayed before reaching red ripe. More chilling injury (CI) developed when C2H4 was applied following heat treatment rather than before. There was more CI in fruit that were 42°C water treated compared with the 38°C air treatment. Less CI developed on fruit that were partially ripened for 2 days at 20°C before a 42°C water treatment rather than following it. At red ripe, nonchilled fruit were firmer than chilled heat treated fruit. Fruit treated in 42°C water were firmer when the heat treatment was applied before the C2H4 treatment rather than following it. Chlorophyll and lycopene content and internal quality characteristics of fruit were similar at the red ripe stage irrespective of C2H4 or heat treatment. Chilling and heat treatments reduced some of the 15 flavor volatiles analyzed. Volatile levels were lower in fruit treated with C2H4 before heat treatment compared with fruit treated with C2H4 following heat treatment. Prestorage heat treatments could allow for storage of mature green tomatoes at low temperatures with little loss in their ability to ripen normally.

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Mustafa Ozgen, Artemio Z. Tulio Jr., Ann M. Chanon, Nithya Janakiraman, R. Neil Reese, A. Raymond Miller, and Joseph C. Scheerens

To investigate phytonutrient accumulation in black raspberries, fruits of `Jewel' and `MacBlack' were harvested at stages from the onset of color development (S1) to ripe fruit (S7). S1–S7 samples were characterized for color reflectance and then frozen at –28 °C within an hour of harvest. Additional ripe fruit were maintained at 20 °C for 3 days to overripen (S8) before freezing. After storage, samples were analyzed for dry weight (DW), total soluble solids (TSS), fructose (FRU), glucose (GLU), and organic acid (ORG) contents; total phenolic (PHE) and anthocyanin (ACY) contents; individual cyanidin glycoside levels (ICG); and antioxidant capacity (FRAP and ABTS) by standard methodology. `Jewel' and `MacBlack' ripened similarly. Chroma values and DW percentage decreased while TSS levels, sugar contents (FRU+GLU), PHE, ACY, the ACY: PHE ratio, and ICG increased with progressive ripening stages (S1–S7). Values of PHE, ACY, and ICG were highly correlated (r < +0.95) with FRAP and ABTS values. ACY levels in S6 fruit were 18% to 23% less than those of S7; lower S6 ACY levels were associated with reduced antioxidant capacity in `MacBlack', but not `Jewel'. Overripened fruit (S8) exhibited increased DW (11% to 25%) and decreased sugar contents (16% to 17%), consistent with moisture and respiratory losses after harvest. After correction for these losses, S7 and S8 levels of PHE, ACY, FRAP, and ABTS were similar in `MacBlack'. However, as `Jewel' overripened, ACY levels and antioxidant activity increased 44% and 22% to 26%, respectively. Our data suggests that significant changes in the antioxidant behavior of black raspberries can occur during the periods surrounding peak ripeness.

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Susan B. Templeton, Martha Marlette, Kirk W. Pomper, and Snake C. Jones

Marketed as a fresh fruit, the pawpaw (Asimina triloba) has a short shelf life, only 2-3 days at room temperature and up to 3 weeks with refrigeration. There is commercial processing potential for pawpaw pulp in juices, ice cream, yogurt, baked goods, and other products. Consumer acceptability of such products needs to be investigated. One hundred and five attendees of the 2nd Annual Pawpaw Field Day at Kentucky State University (KSU), Frankfort, Ky., participated in a tasting of pawpaw products; 56% of tasters were male; 76% were over 40 years of age; 72% of tasters had eaten pawpaw previously. Each item was rated on a scale from 1 = liked it extremely to 7 = disliked it extremely. Pawpaw ice cream was the best-received item (55% of tasters liked it extremely), followed by pawpaw cake with lemon icing, liked extremely by 45%. The pawpaw/grape juice drink was liked extremely by 31% of participants. Three alternative recipes for pawpaw butter were presented; the plain pawpaw butter was liked extremely by 26% of tasters; pawpaw butter prepared with lemon and grape juice was liked extremely by 11%, while the version prepared with orange and lemon was liked extremely by only 8%. Two versions of pawpaw custard were presented. The custard prepared from ripe, mild-fl avored fruit was liked extremely by 42% of tasters, while the custard prepared from mixed under-ripe, over-ripe and bruised fruit was liked extremely by only 16%. Ratings by persons unfamiliar with pawpaw fl avor were significantly lower (P < 0.05) only for the two pawpaw custards; tasters age 40 years or younger gave significantly higher ratings for pawpaw ice cream (P < 0.05) and significantly lower ratings for both pawpaw custards (select, P < 0.05 and mix, P < 0.01) and the pawpaw/grape juice drink (P < 0.05).

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Maria Eloisa G. Quintana and Robert E. Paull

`Solo' papaya (Carica papaya L.) fruit removed at different points from a commercial packing house showed that skin injury due to mechanical damage increased as fruit moved through the handling system. The occurrence of “green islands” -areas of skin that remain green and sunken when the fruit was fully ripe-apparently were induced by mechanical injury. Skin injury was seen in fruit samples in contact with the sides of field bins, but not in fruit taken from the center of the bins. Bruise-free fruit at different stages of ripeness (5% to 50% yellow) were dropped from heights of 0 to 100 cm onto a smooth steel plate to simulate drops and injury incurred during commercial handling. No skin injury occurred, although riper fruit showed internal injury when dropped from higher than 75 cm. Fruit (10% to 15% yellow) dropped onto sandpaper from a height of 10 cm had skin injury symptoms similar to those seen on fruit from the commercial handling system. These results suggest that abrasion and puncture injury were more important than impact injury for papaya fruit. Heating fruit at 48C for ≈6 hours or until fruit core temperature (FCT) reached 47.5C aggravated the severity of skin injury. Delays in the application of heat treatment from dropping did not reduce the severity of skin injury significantly, except for fruit heated 24 hours after dropping. Waxing fruit alleviated the severity of skin injury, whether applied before or after the heat treatment. Skin injury to papaya was caused by abrasion and puncture damage-not impact-and increased during postharvest handling of the fruit. The injury was associated mainly with fruit hitting the walls of wooden bins-bin liners may reduce this injury.

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R.E. McDonald, T.G. McCollum, and E.A. Baldwin

Mature-green `Sunbeam' tomatoes (Lycopersicon esculentum Mill.) were treated in varying order with C2H4, 42 °C water for 1 hour, 38 °C air for 2days, held 2 days at 20 °C (partial ripening), or not treated and then stored at 2 °C (chilled) for 14 days before ripening at 20 °C. Heat-treated fruit stored at 2 °C and transferred to 20 °C ripened normally, while 63% of nonheated fruit decayed before reaching the red-ripe stage. Partially ripened fruit developed more chilling injury, were firmer, were lighter, and were less red in color than fruit not partially ripened. Lycopene content and internal quality characteristics of fruit were similar at the red-ripe stage irrespective of sequence of C2H4 exposure, heat treatment, or a partial ripening period. Of the 15 flavor volatiles analyzed, 10 were reduced by storage at 2 °C, Exposure to C2H4 before the air heat treatment reduced the levels of four volatiles, while C2H4 application either before or after the water heat treatment had no effect on flavor volatiles. Two volatiles were decreased and two were increased by partial vipening, Storage at 2 °C decreased the level of cholesterol and increased levels of campesterol and isofucosterol in the free sterol pool. Exposure to C2H4 before or following heat treatments, the method of heat treatment, and partial ripening had little effect on free sterols, steryl esters, steryl glycosides, or acylated steryl glycosides in the pericarp of red-ripe fruit. A shortor long-term heat treatment of mature-green tomatoes could permit storage at low temperatures with little loss in their ability to ripen normally, whereas partial ripening did not reduce chilling injury.

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Lili Zhou, David A. Christopher, and Robert E. Paull

Papaya (Carica papaya L.) source size and sink strength were modified by a single defoliation or continual defoliation and fruit thinning. Fruit set, development, weight, total sugar (sum of sucrose, fructose, and glucose), sucrose phosphate synthase (SPS), sucrose synthase (SS), and acid invertase (AI) enzyme activities in response to defoliation and fruit thinning were determined. The effects of defoliation and fruit thinning varied with weather conditions, plant growth conditions, and cultivar. Removal of 75% of the leaves significantly reduced new flower production and fruit set, and decreased ripe fruit total soluble solids (TSS), while 50% defoliation did not reduce new fruit set or ripe fruit TSS. When every third leaf from the oldest leaf was not removed, the number of new flowers was reduced by 47% more than when the same number of leaves was removed from the oldest to younger leaves. Continual removal of old leaves reduced new fruit set, fruit weight, and TSS in the 168 day experimental period. Fruit thinning increased new fruit set and ripe fruit TSS. Larger fruit size, faster fruit development, lower respiration rate, and higher sugar contents and AI activity were observed in immature (young) fruit when old fruit were removed. AI activity was reduced during early fruit development and increased again in mature fruit in plants subjected to defoliation, and suggested a role for AI in mature fruit sugar accumulation, while SS activity declined significantly in fruit 154 and 175 days after anthesis and in mature fruit when plants were subjected to continual defoliation. SPS activity was not affected significantly by defoliation or fruit thinning. Source-sink balance was critical for papaya fruit set, development, and sugar accumulation and each mature leaf was able to provide photoassimilate for about three fruit.