Abstract
The ripening, chilling injury and respiratory responses of ‘Hass’ and ‘Fuerte’ avocado fruit (Persea americana L.) were determined at 20°C subsequent to 0 to 5 weeks storage at 10°, 5° and 0°. Fruit held at 10° showed no chilling injury symptoms and were ripe by the third week. No softening or chilling injury symptoms occurred during the 5 weeks at 5° or 0°. However, after transfer to 20° fruit held at 5° and 0° longer than 1 week developed chilling injury and the severity increased as the exposure period increased. Short exposures to 5° and 0° tended to hasten ripening at 20° compared with fruit placed directly at 20°, but fruit held 5 weeks at 5° and 0° took longer to ripen at 20° than control fruit. Fruit placed directly at 20° showed a typical climacteric respiratory pattern which was associated with ripening. Chilling at 5° and 0° for more than 1 week resulted in high initial respiratory rates at 20°, followed by decreasing respiratory rates with no climacteric pattern associated with ripening.
Abstract
Five cultivars of apples (Malus domestica Borkh.) each with 2 different harvest dates were stored in continuous flow controlled atmosphere (CA) at 3% O2 and 3% CO2 at 0°C or 3.3° for 3 to 7 months. Ethylene in the CA was maintained at 3 levels: low (mostly below 1 ppm, maximum 3.8 ppm), 10 ppm and 500 ppm. In comparison with low ethylene, 10 ppm and 500 ppm ethylene in CA did not significantly affect the soluble solids, titratable acids, firmness and sensory evaluated ripeness of ‘Delicious’, ‘Golden Delicious’, ‘Indared’ and ‘Cortland’ apples harvested on either date and of ‘McIntosh’ apples harvested after the onset of climacteric. However, ‘McIntosh’ harvested before the onset of climacteric retained higher acids, firmer texture and were sensory evaluated as less ripe when kept in CA with low ethylene than that with 10 or 500 ppm ethylene. ‘Delicious’ apples stored for 7 months in CA with 10 or 500 ppm ethylene developed severe scald but those in CA with low ethylene did not.
`Golden Delicious' apples (Malus domestica Borkh.) harvested at the preclimacteric and climacteric stages of ripening were stored for up to 8 months at 1C in air and under various controlled atmosphere(s) (CA), including ultralow oxygen (ULO) storage conditions. Aroma volatiles were measured at 2-month intervals in fruit ripened for 10 days at 20C. Fruits harvested at the climacteric stage produced more volatiles during all storage conditions than preclimacteric fruit. All CA storage treatments suppressed aroma production compared to cold storage. The greatest reduction was found under ULO (1% O2) and high CO2 (3%) conditions. A partial recovery of aroma production was observed when CA fruits were subsequently stored for 14 days under cold storage conditions. Suppression of aroma production under ULO conditions seems to be related to low fatty acid synthesis and/or degradation, and is restricted to volatiles having a straight C chain. Production of branched C-chain aroma compounds was suppressed by high CO2 concentrations. The reduced capacity of aroma production during shelf life after ULO storage is confined to apple cultivars producing mainly ester compounds with a straight C-chain, e.g., `Golden Delicious'.
Botanically, “berry crops” are not a homogeneous group, or distinct from other horticulturally defined groups of fruits. Many horticultural “berries” are not berries in a botanical sense and they originate from as wide a variety of floral structures as other fleshy fruits. Nevertheless there are many similarities in fruit development and physiology among horticultural berries and between these and other fruits. An early phase of cell division is followed by cell enlargement, with concomitant accumulation of sugars and organic acids. In the ripening phase, chloroplast to chromoplast transitions, accumulation of vacuolar pigments and cell wall alterations are general phenomena. The climacteric pattern of ripening and regulation by ethylene have attracted most attention in the literature on fruit ripening; this may be appropriate for tree fruits, but many berries are non-climacteric and we have to consider other regulatory mechanisms. Similarly, although cell wall degradation by polygalacturonase has captured attention in other fruits, other softening mechanisms need to be considered for fruits, such as strawberry.
A microarray containing over 10,000 gene fragments was used to link changes in gene expression with changes in aroma biosynthesis in ripening apple (Malus ×domestica Borkh). The microarray was probed with fluorescent-tagged cDNA derived from RNA extracted from `Jonagold' apple skin and cortex tissue representing eight distinct physiological stages spanning 70 days during ripening and senescence. The ripening stages, in chronological order, were: 1) early preclimacteric; 2) late preclimacteric and onset of trace ester biosynthesis; 3) onset of the autocatalytic ethylene and rapidly increasing ester biosynthesis; 4) half-maximal ester biosynthesis and engagement of the respiratory climacteric; 5) near maximal ester biosynthesis, peak in respiratory activity, and the onset of rapid tissue softening; 6) maximal ester biosynthesis prior to its decline, the conclusion of the respiratory climacteric, and the completion of tissue softening; 7) midpoint in the decline in ester biosynthesis and maximal ethylene biosynthesis; and 8) postclimacteric minimum in ester production. Patterns in gene expression reflecting the rise and fall in ester formation were found in some putative genes for beta-oxidation (acyl-CoA oxidase, enoyl-CoA hydratase, and acetyl-CoA acetyl transferase), ester formation (aminotransferase, alcohol dehydrogenase, and alcohol acyl transferase), and fatty acid oxidation (lipoxygenase), but not fatty acid biosynthetic genes. A marked decline coinciding with the onset of ester production was detected in several putative genes for ADH.
Ripening pawpaw [Asimina triloba (L.) Dunal] fruit exhibit climacteric peaks of ethylene and CO2 production 48 to 72 hours after harvest, and thus may be considered climacteric. The development of desirable quality traits and the loss of fruit firmness during ripening is extremely rapid, and a variety of strategies to slow these processes via manipulation of ethylene production and/or response and by more direct techniques like postharvest heat treatment have been attempted. Fruit, branches with fruit, and/or whole trees have been sprayed with ethephon or aminoethoxyvinylglycine to hasten or delay ripening, respectively. After harvest, fruit have been treated with commercial and higher rates of 1-methylcyclopropene for various durations at ambient and cold storage temperatures. Fruit have also been heat-treated at various temperatures, using both brief “shock” treatments above 40 °C and longer periods at 35 °C to 40 °C. In addition, in an attempt to alleviate the loss of ripening capacity as well as the development of injury symptoms from cold storage for longer than 4 weeks, cold-stored fruit were warmed to ambient temperature intermittently and then returned to cold storage. While some effects of the treatments were noted, the responses to all of these treatment strategies have failed to appreciably alter fruit ripening, the rapid loss of firmness, or otherwise maintain fruit quality beyond that without treatment.
The growth regulator 1-methylcyclopropene (1-MCP) is a vapor under physiological conditions and acts by inhibiting the binding of the hormone ethylene to its binding site and a single exposure can temporarily render plant material insensitive to ethylene when applied at the parts-per-billion level. Apple fruit were harvested 1 week prior to the climacteric (harvest 1), at the onset of the climacteric (harvest 2), and 1 week after the onset of the climacteric (harvest 3). Fruit were stored at 0, 5, 10, 15, and 20 °C and were given treatments with 1 ppm 1-MCP on a once-per-week, once-per-2 weeks, once-per-month, and once-per-year basis or were left untreated. In terms of reduced softening, earlier harvested fruit were more responsive to the 1-MCP treatment and the efficacy of 1-MCP was enhanced by repeated application. At 20 °C, control fruit (all harvests) softened to less than 50 N pressure within 20 days. For fruit treated once with 1-MCP, fruit of harvest 1 reached this threshold by 63 days, those of harvest 2 after 56 days and those of harvest 3 by 40 days. Fruit treated on a once-per-month basis began to soften by 56 days for harvest 3, while those of harvest 1 and 2 did not. Fruit treated once per week or once per 2 weeks did not soften relative to initial firmness (68N) during the first 63 days of the study. 1-MCP effectively prevented softening at all temperatures relative to the controls, however, as temperature decreased, the benefits of 1-MCP application became less pronounced. Decay was a significant problem for fruit stored at 15 and 20 °C storage temperatures. Roughly 30% to 60% of the fruit were lost to decay in the first 60 days of the study. 1-MCP application reduced, but did not prevent decay. Storage of 1-MCP-treated apple fruit at elevated temperatures will likely require some means of controlling decay in storage.
AVG was evaluated for its effect on controlling preharvest drop and influencing ripening of `McIntosh' apples in Maine and Massachusetts. AVG consistently and effectively retarded preharvest drop. AVG was superior to NAA and comparable to daminozide in drop control. Dilute or 2× applications were more effective than applications made at lower water volumes. One application of AVG made 4 weeks before anticipated normal harvest was more effective in controlling preharvest drop than split applications of the same amount made earlier or later. In general, AVG delayed ripening as assessed by a retardation in the development of red color, maintenance of flesh firmness, delayed degradation of starch, and a delayed onset of the ethylene climacteric. We conclude that AVG is an effective drop control compound that is also useful as a management tool to extend the harvest window for blocks of `McIntosh' that would otherwise ripen simultaneously. Chemical names used: aminoethoxyvinylglycine (AVG), naphthaleneacetic acid (NAA), succinic acid-2,2-dimethylhydrazide (daminozide, Alar).
The inhibitor of ethylene binding, 1-methylcyclopropene (1-MCP) has been applied to `Gala', `Cortland', `McIntosh', `Empire', `Delicious', `Jonagold', and `Law Rome' apples under air and/or controlled atmosphere (CA) storage conditions. 1-MCP gas concentrations ranged from 0 to 2 mL·L–1. Effects of 1-MCP were greater in CA than air storage. A dose response of internal ethylene concentrations and flesh firmness to 1-MCP was found in cultivars such as `McIntosh' and `Law Rome', whereas in others, such as `Delicious' and `Empire', ripening was generally prevented by all 1-MCP concentrations. We have further investigated the effects of 1-MCP on `McIntosh' by increasing rates of the chemical to 50 mL·L–1, and confirming that fruit of this cultivar respond poorly if fruit have entered the climacteric prior to 1-MCP application. Efficacy of 1-MCP is affected by cultivar and storage conditions, and that successful commercial utilization of the chemical will require understanding of these relationships.
Volatile ester molecules are important contributors to the perception of fruit taste. Biosynthesis of volatile compounds occurs via several biochemical pathways. Ongoing studies have concentrated on alcohol acetyl transferase, the terminal step in the acetate ester synthesis pathway. Our studies on volatile biosynthesis in apples have revealed several interesting phenomena. First, the nature and amount of volatile compounds are cultivarand strain-dependent. Studies with `Delicious' show a relationship between amount of peel coloration and flavor volatile content of tissue. Second, it is possible to manipulate the preharvest growing environment to influence the content of some volatiles in the fruit. Third, generation of volatiles is closely linked to the onset of climacteric ripening. Other experiments show the response of apples to different storage conditions with regard to volatile ester synthesis. In some cultivars softening apparently provides ester precursor molecules, leading us to speculate that there are glycosidically bound intermediates that are liberated by the action of cell-wall degradation.