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Jiwon Jeong, Jeffrey K. Brecht, Donald J. Huber, and Steven A. Sargent

storage life because of excessive tissue softening, which is coordinated by ethylene and has been demonstrated to be a consequence of alteration in cell wall metabolism ( Huber et al., 2001 ; Karakurt and Huber, 2003 ). There are numerous chemical and

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Jiwon Jeong and Donald J. Huber

Pre-ripe `Booth 7' avocado (Persea americana Mill.) fruit, a cross of West Indian and Guatemalan strains, were treated with 0.9 μL·L-1 1-methylcyclopropene (1-MCP) for 12 hours at 20 °C. After storage for 18 days in air at 13 °C, at which time whole fruit firmness values averaged about 83 N, half of the 1-MCP-treated fruit were treated with 100 μL·L-1 ethylene for 12 hours and then transferred to 20 °C. 1-MCP delayed softening, and fruit treated with 1-MCP retained more green color than air-treated fruit when full ripe (firmness 10 to 15 N). 1-MCP affected the activities of pectinmethylesterase (EC 3.2.1.11), α-(EC 3.2.1.22) and β-galactosidases (EC 3.2.1.23), and endo-β-1,4-glucanase (EC 3.2.1.4). The appearance of polygalacturonase (EC 3.2.1.15) activity was completely suppressed in 1-MCP-treated fruit for up to 24 days, at which time the firmness of 1-MCP-treated fruit had declined nearly 80% compared with initial values. The effect of exogenous ethylene applied to partially ripened 1-MCP-treated fruit differed for different ripening parameters. Ethylene applied to mid-ripe avocado exerted no effect on the on-going rate or final extent of softening of 1-MCP-treated fruit, even though polygalacturonase and endo-1,4-β-glucanase activities increased in response to ethylene. β-galactosidase decreased in 1-MCP-treated fruit in response to ethylene treatment. 1-MCP delayed the increase in solubility and depolymerization of water- and CDTA (1,2-cyclohexylenedinitrilotetraacetic acid)-soluble polyuronides, likely due to reduced polygalacturonase activity. At the full-ripe stage, the levels of arabinose, galactose, glucose, mannose, rhamnose, and xylose associated with the CDTA-soluble polyuronide fraction were similar among all treatments. In contrast, the galactose levels of water-soluble polyuronides declined 40% and 17% in control and 1-MCP treated fruit, respectively. Hemicellulose neutral sugar composition was unaffected by 1-MCP or ethylene treatment. The data indicate that the capacity of avocado fruit to recover from 1-MCP-mediated suppression of ripening can be only partially amended through short-term ethylene application and differs significantly for different ripening parameters.

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D. Gerasopoulos and D.G. Richardson

Mature `Anjou' pears (Pyrus communis L.) continuously stored at 20 °C or -1 °C before transfer to 20 °C exhibited differences in the sequence of ripening events up to 100 days. Pears continuously held at 20 °C showed little change in ripening characteristics (chlorophyll, firmness, titratable acidity) for 14 to 28 days, then these characteristics decreased at a daily rate of 1.4% thereafter. A 40% increase in soluble polyuronides paralleled the firmness loss, while ACC did not exceed 0.5 nmol·g-1 until the 84th day, and internal ethylene did not exceed 0.2 μL·L-1 until after 90 days, whereas ACC oxidase activity (and total protein) peaked after 63 days. `Anjou' pears stored at -1 °C showed no changes in chlorophyll, firmness, protein, or total polyuronides for at least 84 d. Despite essentially no change in firmness during -1 °C storage, there was a slow but steady increase (≈15 %) in soluble polyuronides. ACC oxidase activity, expressed as ethylene production, rose to 71 nL·g-1·h-1 and the ACC content increased to almost 1.0 nmol·g-1 by the 84th day. Internal ethylene slowly increased and levelled to 1 μL·L-1 by the 56th day. Satisfaction of a chilling requirement thus appears to favor the development of ethylene synthesis capacity, which on transfer from cold storage to higher temperatures results in enough internal ethylene to rapidly drive the associated ripening mechanisms. Fruit for which the chilling requirement (≥70 days at -1 °C) was met softened in response to accelerated internal ethylene production on transfer to 20 °C for 7 days. However, pears that were not chilled or partially chilled did not sustain the increased ACC levels or ACC oxidase activity. Chemical name used: 1-aminocyclopropane-1-carboxylate (ACC).

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Gustavo H.A. Teixeira and José F. Durigan

they had a reduced effect on the key regulatory enzymes (e.g., polygalacturonase, pectinmethylesterase, and cellulase) that are responsible for the softening process of many fruits ( Chitarra and Chitarra, 2005 ; Kader, 1995 ; Tucker, 1993 ). On the

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Carlos H. Crisosto, David Garner, Harry L. Andris, and Kevin R. Day

A commercial controlled delayed cooling or preconditioning treatment was developed to extend peach (Prunus persica) market life of the most popular California peach cultivars. A 24 to 48 h cooling delay at 68 °F (20.0 °C) was the most effective treatment for extending market life of internal breakdown susceptible peaches without causing fruit deterioration. This treatment increased minimum market life by up to 2 weeks in the cultivars tested. Weight loss and softening occurred during the controlled delayed cooling treatments, but did not reduce fruit quality. Detailed monitoring of these fruit quality changes during the delayed cooling period and proper use of fungicides is highly recommended for success in this new fruit delivery system. Rapid cooling after preconditioning is important to stop further fruit deterioration such as flesh softening, senescence, decay and weight loss. Controlled delayed cooling can also be used to pre-ripen susceptible and nonsusceptible peaches to deliver a ready-to-buy product to the consumer.

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Donald J. Huber

the effects of 1-MCP on fruit softening ( Huber et al., 2003 ). A well-maintained and comprehensive literature base for responses of horticultural crops to 1-MCP is also available ( Watkins and Miller, 2005 ). Accordingly, this article takes a

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James W. Rushing and Donald J. Huber

Enzymically active cell wall isolated from mature-green and ripening tomato (Lycopersicon esculentum Mill cv. `Rutgers') fruit was employed to investigate the mobility of the enzyme polygalacturonase (PG, EC 3.2.1.15). Cell walls from mature-green `Rutgers' fruit or from the ripening mutant rin, which alone exhibits little or no release of pectin, were unaffected by the addition of enzymically active cell wall from ripening `Rutgers' fruit, indicating that PG is either not transferred at all or is not transferred to sites of pectin hydrolysis. The quantity of pectin released by the addition of soluble PG to enzymically active wall depended on the quantity of enzyme added. Similar data were obtained using purified PG2. Pectin solubilization from all wall isolates exhibiting enzymically mediated pectin release diminished with time; however, transfer to fresh buffer initiated a resumption of autolytic activity, indicating that an inhibitor is released during the course of pectin hydrolysis.

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Shimon Meir, Sonia Philosoph-Hadas, Giora Zauberman, Yoram Fuchs, Miriam Akerman, and Nehemia Aharoni

Fluorescent products (lipofuscin-like compounds) of lipid peroxidation, which accumulate with age, were extracted from `Fuerte' avocado (Persea americana Mill.) peels during ripening. Fractionation and analysis of these fluorescent compounds (FCs) was carried out by an improved method, based on separation of FCs from-chlorophyll by Sep-Pak silica cartridges. A sharp rise in FCs content was found 2 days after harvest in avocado fruits stored at 22C, and ethylene enhanced this rise 3-fold on the 4th day. The accumulation of FCs preceded by at leasts days the onset of climacteric ethylene and respiration and by 2 days the decrease in fruit firmness. Moreover, a 6-foId increase in the FCs concentration occurred during 1 to 2 weeks of storage at SC, but the avocado fruits did not show any other detectable signs of ripening. These results suggest that lipid peroxidation may be regarded as one of the earliest detectable processes occurring during fruit ripening. Thus, an increase of FCs in peel may be employed as a horticultural characteristic for estimating initiation of ripening in avocado fruit.

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B. Fils-Lycaon and M. Buret

Pectic fractions soluble in water, oxalate, or hydrochloric acid were prepared from an alcohol-insoluble residue of cherry (Prunus avium L., `Bigarreau Napoléon') tissue. Galacturonic acid and neutral sugar contents were measured during the ripening and overripening of fruit. Fruit firmness was also determined. The changes occurring during fruit development gave prominence to three physiological stages and suggested the progressive degradation of the middle lamella and primary cell wall. The firmness measurement was related to the equilibrium between the relative parts of these pectic fractions.

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Jennifer R. DeEll, H.P. Vasantha Rupasinghe, and Dennis P. Murr

`Cortland' is an apple cultivar with inherent poor storeability because of excessive vulnerability to the development of superficial scald in long-term storage. The objectives of this investigation were to evaluate the potential of the potent ethylene action inhibitor 1-methylcyclopropene (1-MCP; EthylBloc®) to counteract this constraint and to develop some basic procedures for its exposure. Eight hours after harvest, fruit were exposed to 1.0 mL·L–1 1-MCP for 0, 3, 6, 9, 12, 16, 24, or 48 h at 3, 13, or 23 °C. Following exposure, fruit were placed at 0 to 1 °C in air for 120 days, after which time they were removed to 20 °C and held 7 days for post-storage assessment of ripening and to allow development of physiological disorders. In general, and within our experimental limits, the higher the temperature of 1-MCP exposure the shorter the required exposure time to obtain similar effects. The desired effectiveness of 1-MCP could be achieved by exposing fruit for at least 3 h at 23 °C, for 6 h at 13 °C, or for 9 h at 3 °C. 1-MCP-treated apples were consistently 2 kg firmer than untreated apples. Scald incidence in untreated fruit after 120 days at 0 to 1 °C and 7 days at 20 °C was 100%, whereas 1-MCP reduced scald by 95% in treatments of long enough duration at any particular temperature.