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  • Author or Editor: Elizabeth J. Mitcham x
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The produce industry faces a future with reduced access to postharvest fungicides. It has become increasingly important to reduce commodity susceptibility to decay and to develop non chemical methods for decay control. Heat therapy has been demonstrated to be effective for control of numerous decays and is currently practiced for control of anthracnose in mangoes and papayas and for decay control in oranges. The limitations to heat therapy include the often tine line between effectiveness and commodity injury and the lack of residual protection. Modified atmosphere has been used effectively for many years by the California strawberry and raspberry industry to allow cross-country shipment of a commodity on which no postharvest fungicides are used. It has been shown that CO2 concentrations of 15% and higher inhibit the growth of many fungi, including Botrytis cinerea, the main cause of strawberry decay. Many commodities cannot tolerate 15% CO2 for an extended period of time. However, the short term (1 to 3 weeks) tolerance has not been determined. With the loss of postharvest fungicides, we may find that many commodities could benefit from shipment under high CO2, as have strawberries. The combination of heat therapy and MA will also be discussed.

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Controlled atmospheres have been proven an effective postharvest disease deterrent for strawberries both in transport and storage. However, these treatments do not provide residual protection once the commodity is removed from the atmosphere, and the atmospheres can cause off-flavors in the fruit. Elevated oxygen atmospheres are a novel addition to this technology and could potentially provide better decay control without the harmful effects on fruit flavor aspects. Elevated oxygen will potentially discourage microbial growth, as anaerobes grow best under very low oxygen levels and aerobes grow best under atmospheric oxygen. Threshold elevated oxygen levels to prevent Botrytis cinerea growth in vitro and in vivo on strawberry were assessed. Botrytis cultures (mycelial plugs and spores) and fresh strawberry fruit were exposed to 21%, 40%, 60%, and 80% oxygen atmospheres at 5 °C for 5, 7, and 14 d. Growth of cultures from mycelial plugs was evaluated after treatment and during post-treatment incubation by measuring the diameter of the fungus. Spore germination and germ tube elongation were evaluated every 24 h for 3 days after treatment by counting the number of germinated spores and measuring elongation, respectively. Strawberry quality including firmness, color, soluble solids, titratable acidity, ethylene production and respiration rates, and presence of defects were evaluated upon removal from the elevated oxygen atmospheres as well as after 1, 3, and 5 d storage in air at 20 °C simulating market conditions.

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Mature green mango (Mangifera indica L.) fruit were heated (100% RH) at 50C for 120, 180 or 240 min or 46C for 160, 220 or 280 min. The rate of mesocarp color (CIE a*) development was reduced in treated fruit, particularly in inner tissue. Rate of softening of mesocarp tissue was reduced after heat treatment; inner more than outer. Fruit treated at 50C remained more firm than control fruit 9 days after treatment, whereas fruit treated at 46C were more firm than controls 3 days after treatment, but were similar by 9 days. Electrolyte leakage from inner mesocarp tissue disks increased with increasing time at 50C, but was unchanged in fruit treated at 46C. However, after 3 days, electrolyte leakage returned to control levels. Ethylene-forming enzyme (EFE) activity of inner meso-carp tissue was greatly reduced in fruit treated at 50C (all times), and at 46C (220 and 280 min). After 3 days, EFE activity of fruit from most treatments had recovered to levels higher than controls. These data indicate that fruit may be able to recover from heat stress. Mild heat stress may increase postharvest shelf life by reducing the rate of softening.

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Peaches and apricots were obtained at harvest. One-half were inoculated with the brown rot organism (Monilinia fructicola) and incubated overnight before immersion in 52C water for 2.5 and 2 minutes, respectively. Fruit were placed in storage at SC in air, 2% O2 and 15% CO2, or 17% O2 and 15% CO2 for 5 or 15 days before ripening at 20C. For peach, controlled atmosphere (CA) had no influence on decay while hot water significantly reduced decay incidence and severity. For apricot, after 15 days cold storage, both hot water and controlled atmosphere storage reduced decay incidence and severity. CA with 2% O2 and 15% CO2 controlled decay better than 17% O2 and 15% CO2. Growth and sporulation of Monilinia fructicola in air and CA was also evaluated in vitro. The combination of heat and CA controlled decay better than either treatment alone. The hot water treatment resulted in minor surface injury on peaches while apricots were not injured. Fruit were evaluated after storage for firmness, soluble solids, and titratable acidity. Accumulation of ethanol and acetaldehyde as a result of CA storage was monitored.

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`Keitt' and `Tommy Atkins' mango (Mangifera indica L.) fruit were evaluated for selected ripening criteria at six ripening stages, from mature green to overripe. `Tommy Atkins' mangos developed more red and yellow pigmentation (CIE a* and b*) in peel and mesocarp tissues than `Keitt'. The outer mesocarp of `Keitt' remained firm longer than `Tommy Atkins', and the inner mesocarp was softer than the outer at each stage in both cultivars. Cell wall neutral sugars, particularly arabinosyl, rhamnosyl, and galactosyl residues, decreased with ripening in both cultivars. `Keitt' had more loosely associated, chelator-soluble pectin, accumulated more soluble polyuronides, and retained more total pectin at the ripe stage than `Tommy Atkins'. Both cultivars had similar polygalacturonase (EC 3.2.1.15) activity which increased with ripening. The amount and molecular weight of cell wall hemicellulose decreased with ripening in both cultivars. These data indicate that enzymatic and/or nonenzymatic processes, in addition to polygalacturonase activity, are involved in the extensive softening of mango fruit.

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Cell wall synthesis during development and ripening of `Rutgers', rin and nor tomato (Lycopersicon esculentum Mill.) fruit was quantified by monitoring incorporation of 14C into outer pericarp cell walls after pedicel injection of (U-14C) - sucrose. Fruit color (Hunter “a” and “b” values) and firmness (Instron) were also monitored. 14C-Incorporation continued throughout development and ripening in `Rutgers' cell walls and exhibited a transient increase from late maturegreen to the turning stage. Incorporation of 14C into cell walls of rin pericarp tissue was similar to `Rutgers' at 20 days pest-anthesls (DPA) (immature-green) but decreased to a level similar to red `Rutgers' fruit by 35 DPA. Incorporation of 14C into nor pericarp cell walls was low throughout the experimental period (20 to 75 DPA). In contrast to previous reports, rin and nor pericarp tissue exhibitad a decrease in firmness of the outer pericarp. However, the rate of softening was slower than in `Rutgers'. Pericarp tissue from rin and nor fruit at 70 and 75 DPA, respectively, resisted compression as much as pink `Rutgers' pericarp tissue.

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Ripening behavior of `Bartlett' pears (Pyrus communis L.), with or without ethylene (C2H4) treatment, was assessed at harvest, and after 2, 4, 6 and 12 weeks of cold storage at –1 °C. Fruit exhibited increasing rates of C2H4 production and consequently faster ripening rates with increased length of cold storage. Ripening characteristics were influenced by storage duration, but to different degrees. The data indicate that the threshold C2H4 concentration for softening may be lower than that for color change from green to yellow. Ethylene treatment for 24 h at harvest resulted in a rate of ripening equivalent to that following cold storage for 2 to 4 weeks, depending on the orchard location. Storage for 12 weeks significantly increased C2H4 production upon transfer to ambient temperature, indicating that fruit were reaching the end of their storage life. `Bartlett' pears may ripen to a firmness of 14 N (ready to eat) at 20 °C within 2.5 to 7 days depending upon the duration of prior cold storage.

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Non-SO2-fumigated `Thompson Seedless' table grapes (Vitis vinifera L.) were stored at 5 or 20 °C for 6 and 4.5 days, respectively, in air or one of four insecticidal controlled atmospheres (ICA); 0.5% O2 + 35% CO2; 0.5% O2 + 45% CO2; 0.5% O2 + 55% CO2; or 100% CO2. The fruit were evaluated for weight loss, berry firmness, soluble solids concentration (SSC), titratable acidity, berry shattering, rachis browning, berry browning, and volatiles (acetaldehyde and ethanol). Fruit quality was not affected at 5 °C with the exception of greater rachis browning in fruit treated with 0.5% O2 + 45% CO2. At 20 °C, ICA treatments maintained greener rachis compared to the air control; however, SSC was reduced in the fruit treated with 55% and 100% CO2. At both temperatures, ICA induced the production of high levels of acetaldehyde and ethanol. Ethanol concentrations were two-thirds lower at 5 °C than at 20 °C. Consumer preference was negatively affected by some ICA treatments for grapes kept at 20 °C, but not by any of the treatments at 5 °C. Preliminary data for mortality of omnivorous leafroller pupae (Platynota stultana Walshingham), western flower thrips (Frankliniella occidentalis Pergande) adults and larvae, and pacific spider mite (Tetranychus pacificus McGregor) adults and larvae indicate that many of the ICA treatments would provide significant insect control.

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Apple (Malux ×domestica Borkh., cv. Fuji) fruit were harvested from two California orchards 190 and 210 days after full bloom and from an additional three orchards at 190 days after full bloom. Fruit were immediately exposed to 20 or 50 kPa CO2 in air at 20 °C. Area of flesh browning and tissue ethanol, acetaldehyde, and ethyl acetate concentrations for individual fruit were determined immediately before exposure and after 3 and 7 days (20 kPa) or 1 and 3 days (50 kPa) exposure to CO2. Area of flesh browning and concentrations of all compounds increased with increasing duration of exposure to high CO2, were greater in response to 50 kPa than to 20 kPa CO2, and were greater for fruit harvested later in the season. For individual orchards and for individual fruit within most orchards, greater flesh browning was associated with higher acetaldehyde concentrations after 7 days exposure to 20 kPa CO2 or 3 days exposure to 50 kPa CO2. Similarly, flesh browning was positively correlated with ethanol concentrations after 7 days at 20 kPa CO2, but was not related to tissue ethyl acetate concentrations at either CO2 partial pressure. However, higher production of ethanol, acetaldehyde, or ethyl acetate relative to flesh browning occurred during exposure to 50 kPa than to 20 kPa CO2. This suggests that the relationship between accumulation of these compounds and CO2-induced flesh browning in `Fuji' is not simply causal.

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