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- Author or Editor: Jeffrey K. Brecht x
Ethylene production by developing tomato fruit (Lycopersicon esculentum Mill., cv. Sunny) increased 3- to 5-fold at the time of gel formation in the locules, followed by a larger (20-fold) increase at the breaker stage. When the levels of ACC and the activities of ACC synthase and ethylene-forming enzyme (EFE) were measured in different portions of the fruit during maturation, the first increases were observed in the locular tissue coincident with gel formation, followed by changes in the placental and columella tissue. Later changes in ACC, ACC synthase, and EFE in the radial and outer pericarp corresponded to the marked increased in ethylene production that occurred at the breaker stage. Treatment of immature fruit with 50 μl·liter−1 ethylene enhanced the rate of gel formation markedly with no apparent lag time, but the stimulation was dependent on continuous presence of ethylene. These results indicate that the onset of ethylene production occurs in the locule tissue of green tomato fruit prior to its initiation in the pericarp and that the locule cells may develop greater sensitivity to ethylene at an earlier stage than pericarp cells. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).
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.
Abscission of cluster tomatoes commonly limits product marketability in the retail environment. Ripening and exogenous ethylene exposure are assumed to play important roles in cluster tomato fruit abscission. `Clarance' and `DRW7229' fruit harvested at either mature green or partially ripened stages did not abscise during storage for 2 weeks at 20 °C and 95% to 100% relative humidity (RH), although respiration and ethylene production indicated that all fruit reached the postclimacteric stage. Exogenous ethylene (1 or 10 ppm) exposure for 8 days at 20 °C and 95% to 100% RH also did not induce fruit abscission for either cultivar, although pedicel and sepal yellowing were observed. Fruit from clusters stored at 20 °C and 20% or 50% RH abscised if sepal shrivel became noticeable before the fruit reached the full red ripeness stage, while no abscission occurred in fruit that reached the full red stage prior to the appearance of sepal shrivel; no fruit stored in 95% to 100% RH abscised. Fruit that ripened prior to the appearance of sepal shrivel were “plugged” (i.e., tissue underlying the stem scar was pulled out) if manual fruit detachment from the pedicel was attempted. These results indicate that there is an interaction of water loss and fruit ripening in promoting abscission zone development in cluster tomatoes.
Bruising of strawberry (Fragaria ×ananassa Duch.) fruit is a common mechanical injury that reduces product value. Wound-induced ethylene may accelerate deterioration or decay, affecting strawberry quality and shelf life. However, bruising susceptibility varies among strawberry cultivars. In this study, cultivars Monterey, Sweet Sensation, Radiance, and two proprietary cultivars (Cultivar A and Cultivar B) from a private breeding program were investigated to evaluate their bruising susceptibility and wound response. Bruising consisted of dropping a 28-g steel ball from 27 cm onto individual fruit; unbruised fruit were the primary control, while fruit exposed to 1 μL·L−1 ethylene were used as a check for ethylene response. All fruit were stored at 20 °C, 90% relative humidity (RH), with respiration and ethylene production measured at 2-hour intervals for 24 hours. Appearance observations were recorded daily until decay onset. Peak respiration rates of 30–40 mL CO2·kg−1·h−1 mostly occurred within 4 hours (‘Cultivar B’) to 6 hours (‘Cultivar A’ and ‘Sweet Sensation’) after bruising, except ‘Monterey’, which peaked at 60 mL CO2·kg−1·h−1 in 2 hours, and ‘Radiance’, which reached 70 mL CO2·kg−1·h−1 in 6 hours. Maximum ethylene production rates after bruising were 0.05 to 0.06 μL·kg−1·h−1 for ‘Monterey’, ‘Cultivar A’, and ‘Cultivar B’, 0.10 μL·kg−1·h−1 for ‘Sweet Sensation’, and 0.20 to 0.37 μL·kg−1·h−1 for ‘Radiance’. ‘Cultivar B’, with the lowest ethylene production, exhibited the lowest overall bruising severity, whereas ‘Radiance’, with the highest ethylene production, exhibited the most severe bruising-induced water soaking, and the other cultivars were intermediate, although ‘Monterey’ bruises were more discolored than those of the other cultivars. ‘Monterey’, ‘Radiance’, and ‘Sweet Sensation’ showed more yellowing and browning of the calyx in response to both bruising and ethylene exposure than ‘Cultivar A’ and ‘Cultivar B’. Except for ‘Cultivar B’, bruising and ethylene exposure increased decay severity.
Enzymatic browning is a serious quality limitation for fresh-cut potato (Solanum tuberosum L.) that has been successfully controlled by heat treatment in other commodities. The use of brief heat treatments with 55 °C water (HW) applied to ‘Russet Burbank’ tubers for 10, 20, 30, or 40 min before cutting was evaluated for potential implementation to control tissue browning. After heat treatment, tubers were held at 20 °C for 0 or 1 day before peeling and slicing. Control tubers were not previously immersed in hot water. All slices were placed in perforated plastic bags and stored at 5 °C for 6 days. Exposure to HW for 30 or 40 min caused severe heat injury. Browning developed in all treatments as indicated by color measurements and discoloration scores (index of extent of discolored area on the slice surface) during storage. Hot water treatment for 10 min best reduced browning, but only when treated tubers were stored intact for 1 day at 20 °C before cutting, as indicated by discoloration scores and changes in L*, a*, and Ho values, which were significantly different from either the control or the other HW treatments. Generally, the severe browning that developed in control slices during storage was associated with significant increases of 25% and 71% in phenolic content and antioxidant capacity, respectively. On the other hand, phenolic synthesis increased by only 6.25% to 13.2% in HW-treated slices during storage and polyphenoloxidase (PPO) activity was 24% to 31% lower compared with the activity before storage. Immersing potato tubers in 55 °C water for 10 to 20 min followed by storage at 20 °C for 1 day before processing reduced but did not prevent browning of peeled slices in terms of color changes and discoloration score. There was no significant correlation between browning and phenolic content or PPO activity.
Sweet potatoes (Ipomoea batatas L.) were exposed to low O2 and high CO2 for 1 week during curing or subsequent storage to evaluate the use of controlled atmospheres (CA) as insecticidal treatments for sweet potatoes infested with sweet potato weevil (Cylas formicarius elegantulus). Sweet potato roots tolerated 8% O2 during curing, but, when exposed to 2% or 4% O2 or to 60% CO2 plus 21% or 8% O2, they were unsalable within 1 week after curing, mainly due to decay. Exposure of cured sweet potatoes to 2% or 4% O2 plus 40% CO2 or 4% O2 plus 60% CO2 for 1 week at 25C had little effect on postharvest quality. However, exposure to 2% O2 plus 60% CO2 resulted in increased decay, less sweet potato flavor, and more off-flavor. These results indicate that exposure of sweet potatoes to O2 and CO2 levels required for insect control is not feasible during curing, but that cured sweet potatoes are capable of tolerating CA treatments that have potential as quarantine procedures.
Treatment of ‘Fairlane’ nectarines [Prunus persica (L). Batsch] with as high as 500 ppm C2H4 during 1 week of storage at 0 or 10°C, or treatment of ‘Flamekist’ nectarines with up to 100 ppm C2H4 for as long as 4 weeks at 0 or 10°, had no effect on the rate of color change or softening during storage or subsequent ripening periods at 20° in air relative to air storage. Treatment of ‘Flamekist’ nectarines with 100 ppm C2H4 for 1 week at 0 or 10°, however, resulted in maximal C2H4 production rates upon transfer to 20° in air that were approximately 60 and 40% less, respectively, than fruits stored in air or treated with 1 or 10 ppm C2H4 during storage.
The rise in C2H4 production during nectarine [Prunus persica (L.) Batsch] fruit ripening at 20°C was accompanied by an increase in the level of 1-aminocyclo-propane-1-carboxylic acid (ACC) and ACC synthase activity. Activity of the C2H4-forming enzyme (EFE) also increased during ripening, but the level was at least 2-times greater than the C2H4 production rate at all stages. C2H4 treatment significantly increased C2H4 production rate, ACC accumulation, and ACC synthase activity. Ability to convert ACC to C2H4, however, was reduced following C2H4 treatment. An increase in total C2H4 production at 20° following storage of nectarines at 0° for up to 4 days was attributable to enhanced ACC synthase activity. Exposure to C2H4 at 0° for more than 4 days reduced C2H4 production and EFE activity during ripening. Increased accumulation of ACC and lowered EFE activity following prolonged C2H4 treatments at 0° suggests that C2H4 production during ripening of fruit held under these conditions is limited by slowed conversion of ACC to C2H4.
The relationship between the ripening behavior and C2H4 production of 4 slow-ripening nectarine [Prunus persica (L.) Batsch] genotypes was investigated. While there was no change in C2H4 production and little ripening in fruit kept for one month in air at 20°C, continuous exposure to 1300 μl·liter−1 propylene (C3H6) stimulated ripening and C2H4 production in these genotypes. The concentration of 1-aminocyclopropane-1-carboxylic acid (ACC) in freshly harvested fruit was less than 0.05 nmol·g−1 and rose 6- to 8-times during the rise in C2H4 production. ACC levels remained low in preclimacteric fruit of all genotypes except P19-70, in which ACC concentration increased without an accompanying increase in C2H4 production. Wounding had little effect on C2H4 production by these 4 genotypes, but addition of one mm ACC stimulated C2H4 production by tissue plugs 35 to 70 fold. Delaying the harvest by up to 6 weeks had no effect on fruit weight or firmness, but flesh color and pH increased while titratable acidity and soluble solids content decreased; the onset of C2H4 production during storage at 20° was advanced, while the ability to convert ACC to C2H4 declined. In no case did C2H4 production rates by these fruit reach the levels of normal nectarine genotypes. We conclude that these slow-ripening genotypes lack the capacity to produce normal C2H4 levels for nectarines.