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- Author or Editor: Dennis P. Murr x
- HortScience x
`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.
Sequential decreases or increases in the levels of O2 in controlled atmosphere (CA) were investigated as techniques to improve fruit quality of `McIntosh' apples (Malus ×sylvestris [L.] Mill. var. domestica [Borkh.] Mansf.), a cultivar that tends to soften rapidly in storage. Precooled fruit that were harvested at optimum maturity for long-term storage were placed immediately in different programmed CA regimes. In the first year, CA programs consisted of 1) `standard' CA (SCA; 2.5–3.0% O2 + 2.5% CO2 for the first 30 d, 4.5% CO2 thereafter) at 3 °C for 180 d; 2) low CO2 SCA (2.5–3.0% O2 + 2.5% CO2) at 3 °C for 60 d, transferred to low O2 (LO; 1.5% O2 + 1.5% CO2) at 0 or 3 °C for 60 d, and then to ultralow O2 (ULO; 0.7% O2 + 1.0% CO2) at 0 or 3 °C for 60 d; and 3) ULO at 3 °C for 60 d, transferred to LO at 0 or 3 °C for 60 d, and then to SCA or low CO2 SCA at 0 or 3 °C for 60 d. In the second year, the regimes sequentially decreasing in O2 were compared with continuous ULO and SCA. After removal from storage, apples were held in ambient air at 20 °C for a 1-week ripening period. Fruit firmness was evaluated after 1 and 7 d at 20 °C, whereas the incidence of physiological disorders was assessed only after 7 d. Lowering the temperature while decreasing O2 was the best CA program with significant increased firmness retention during storage and after the 1-week ripening period. Reduced incidence of low O2 injury in decreasing O2 programs and absence of core browning at the lower temperature were also observed.
Traditional hand compression firmness scores of iceberg lettuce (Lactuca sativa L.) heads were compared with force-deformation data collected from parallel-plate compression tests conducted with a universal testing machine. Sample deformation was measured over a load range of 30 to 40 N. A quadratic response surface best described the relationship between hand firmness scores (1 to 5 scale) and three measurements of sample deformation (mm). Sample deformation was as precise as hand compression in measuring lettuce firmness, and it provided improved reproducibility by eliminating much of the human error. Although adequate for most firm heads, the predictive ability of the statistical model was weak for soft heads (when the hand firmness score was <2), and for heads with inconsistencies in firmness because of uneven leaf distribution. The minimum sample size required to determine accurately the mean firmness score (±0.5 units) of a population of harvested lettuce was ≈20 heads. This may be a disadvantage, since sampling one head requires ≈1.5 minutes. Overall, the instrument-based method measures lettuce firmness as precisely as the hand compression method, and provides a standardized, objective measurement for postharvest researchers when exchanging or reporting firmness data.
Chlorophyll fluorescence responds to a range of environmental stresses that affect horticultural crops. This technique has been used successfully to evaluate the quality of commodities after exposure to a number of postharvest stresses such as chilling, heat, and atmospheric stress. As well, chlorophyll fluorescence measurements have been incorporated as the main characteristics in shelf-life prediction models. Our objective was to evaluate the use of chlorophyll fluorescence measurements at harvest to predict the shelf-life of `Iceberg' lettuce. It was hypothesized that storage potential is influenced by the degree of stress induced by field conditions and that different cultivars, although grown under the same conditions, experience varying degrees of stress that can be detected by fluorescence measurements at harvest, even in the absence of visual differences in quality. The utility of fluorescence measurements was limited by inconsistencies in the development of the heads, such as maturity and leaf formation, and by variation among different areas of the same leaf. Fluorescence data from a homogeneous group of heads revealed that the variation associated with different areas of the same leaf was larger than that associated with measurements from different heads. Also, fluorescence readings from one leaf differed from those taken from any non-adjacent leaves. These sources of variation, along with strong cultivar-dependant differences in the fluorescence signal, were quite large, and hence, any trends in fluorescence measurements related to storage potential were not observed. Therefore, chlorophyll fluorescence at harvest does not appear to be a good predictor of lettuce storability.
Chlorophyll fluorescence was evaluated as a rapid and nondestructive technique to detect low-O2 or high-CO2 stress in apples (Malus domestica Borkh.) during storage. `Marshall' McIntosh apples were held for 5, 10, 15, 20, or 25 days at 3C in 1) standard O2 (2.5% to 3%) and low CO2 (<1%), 2) low O2 (1% to 1.5%) and low CO2 (<1%), 3) standard O2 (2.5% to 3%) and standard CO2 (4% to 4.5%), or 4) standard O2 (2.5% to 3%) and high CO2 (11% to 12%). Only 10% of the apples had skin discoloration after 5 days in 1% to 1.5% O2; 80% developed skin discoloration after 20 days in low O2. Small desiccated cavities in the cortex, associated with CO2 injury, developed in 10% of the apples after 20 days in 11% to 12% CO2. Five days in 1% to 1.5% O2 or 11% to 12% CO2 caused variable fluorescence (Fv) of apple fruit to decrease compared to those held in standard atmospheres. Additional exposure did not significantly affect Fv in either the low-O2 (1% to 1.5%) or high-CO2 (11% to 12%) treatment. Our results suggest that chlorophyll fluorescence techniques can detect low-O2 and high-CO2 stress in apples before the development of associated disorders.
Glutathione S-transferase (GST) is a ubiquitous and constitutive enzyme that is involved in numerous cellular activities including the amelioration of oxidative stresses caused by the presence of xenobiotics and reactive oxygen species. In the present study, a glutathione S-transferase was extracted, purified, and partially characterized from two types of pome fruits. Pear (Pyrus × communis L., cultivar D'Anjou) and apple (Malus × domestica Borkh., cultivar Delicious) fruit were tested. The glutathione S-transferase was extracted using traditional methods, and purified using a combination of ammonium sulfate precipitation, dialysis, and GST-specific affinity chromatography. The GST enzyme was subsequently eluted from the column and concentrated prior to characterization studies. A purified fraction from the column was loaded onto an SDS-PAGE gel, and resulted in a single band with an apparent molecular weight of ≈26 kDa. This band was excised and used for MALDI-TOF/MS peptide mass fingerprint studies, and also served to confirm the apparent mass of the protein (25969 Da). The ExPASy software was used for the peptide mass fingerprint study, where the digest of the GST using trypsin was compared to a theoretical digest of an Arabidopsis GST, and resulted in two peptides of significant mass homology. The purified GST was also tested for enzyme activity using the standard assay substrate of 1-chloro-2,4-dinitrobenzene and reduced glutathione. Total GST protein extracted from `D'Anjou' pear was 0.532 mg·mL-1, while `Delicious' apple contained 0.127 mg·mL-1. The activity of GST enzymes may play a role in minimizing oxidative stress injury in stored pear and apple tissues.
Preconditioning, holding fruit at 10, 17.5, or 21 °C temperatures for up to 7 days before placement in cold storage, was inconsistent in its effect on soft scald and soggy breakdown in ‘Honeycrisp’ apples in Maine and Ontario. In Ontario, 4 days of preconditioning at 21 °C increased soft scald in 1 year but had no effect in the next year. Five d of preconditioning at 10 °C reduced soft scald and had no effect on soggy breakdown in 1 year but reduced it the next year. In Maine, 5 days preconditioning at 17.5 °C was effective in reducing soft scald and/or soggy breakdown in 2002 to 2007 when starch index at harvest was 5.9 to 7.2. Seven days of preconditioning at 17.5 °C increased soggy breakdown with an early harvest in two orchards but only in one of two orchards with a later harvest. This same preconditioning had no effect on soft scald with the first harvest but reduced it with the second. In the next year, the same preconditioning treatment increased soft scald and soggy breakdown with an early maturity but had no effect with a later maturity in one orchard but not in fruit from another. Conditions during preconditioning and subsequent cold storage temperatures varied from previous recommendations, and this may be why preconditioning was not consistent in our studies and in some cases increased chilling disorders.
Wounding during processing triggers physiological reactions that limits shelf-life of fresh-cut apples. Exposure of `Empire' and `Crispin' apples at harvest to the ethylene antagonist 1-methylcyclopropene (1-MCP, SmartFresh™) on the maintenance of fresh-cut apple quality was evaluated in combination with post-cut dipping of NatureSeal™. Efficacy of 1-MCP on fresh-cut physiology and quality depended on the storage duration and apple cultivar. Ethylene production and respiration of apple slices were inhibited by 1-MCP but not by NatureSeal. Total volatiles produced by fresh-cut apples was not affected by the treatments. 1-MCP influenced the quality attributes of fresh-cut apple slices prepared from apples stored either 4 months in cold storage or 6 months in controlled atmosphere. Enzymatic browning and softening of the cut-surface, total soluble solids, and total microbial growth were suppressed by 1-MCP in `Empire' apples. Overall, the influence of 1-MCP on quality attributes in `Crispin' apple slices was marginal. NatureSeal consistently maintained the firmness of fresh-cut apple slices held at 4 °C for up to 21 days. The additive effect of 1-MCP in the maintenance of apple quality is an advantage for processing and marketing of fresh-cut apples.
Flesh softening is a major quality parameter that can limit long-term storage of apple cultivars. This study investigated the combined effects of preharvest AVG (Retain™) application, 1-methylcyclopropene (1-MCP; EthylBloc™) exposure at harvest, and commercial controlled atmosphere (CA) storage (2.0% O2 + 2.5% CO2) on flesh softening of `Empire' apple. Treatments were assigned in a split-split-plot experimental design; AVG and no AVG application as the main-plot, CA and air storage as the sub-plots, and 0, 0.1 0.5, 1.0 mL·L–1 1-MCP as the sub-sub-plots. Apples were removed from storage at 70 and 140 days after harvest and kept up to an additional 2 weeks at 20 °C for post-storage assessment of ripening. Preharvest AVG application of `Empire' fruit delayed maturation slightly as determined by starch index at harvest, but did not affect fruit size at harvest nor flesh softening in storage. All levels of 1-MCP were equally effective in controlling fruit softening both in air and CA, as 1-MCP-treated fruit were ≈2.5 kg firmer than untreated fruit. This firmness advantage was still evident even after 2 weeks at 20 °C, with CA-stored fruit holding their firmness the best. When all three technologies were combined, treated fruit were overall 156% firmer than control fruit (no AVG, no 1-MCP, air-stored). As well, ethylene production and emanation of aroma volatiles were reduced significantly in these fruit. Therefore, the synergism of AVG, 1-MCP and long-term CA storage could potentially hold flesh firmness and other ripening parameters of apples to values near those found at harvest.
`Gala' apples (Malus × domestica Borkh) were harvested at optimum maturity for long-term storage, precooled overnight at 0 °C, treated with 1 μL·L-1; 1-methylcyclopropene (1-MCP) for 24 hours at 0 °C, and then placed in controlled atmosphere (CA) to determine the storage regime that would have the least negative impact on post-storage aroma volatile production. Fruit were stored at 0° and 2.5° C in ultra low oxygen (0.6% O2 -0.6% CO2; ULOCA), low oxygen (1.2% O2 -1.2% CO2; LOCA) and standard (2.5% O2 -2.5% CO2; SCA) CA for 120 and 240 days, and in ambient air for 60, 90, 120 and 150 days. Post-storage fruit volatiles were quantified by headspace analysis using a solid-phase micro-extraction (SPME) probe and FID-GC, and key volatiles were identified by GC-MS. Fruit volatile production was greatest at harvest, and decreased thereafter for fruit held in air and CA for up to 150 or 240 days, respectively. 1-MCP treatment resulted in reduced rates of respiration, ethylene and volatile production, regardless of storage regime, and resulted in a reduced production rate of all the major volatile compounds, including esters, alcohols, acids, aldehydes and ketones. Post-storage volatile production was the least in fruits removed from 0 °C in ULO, followed by LO, SCA, and then air. 1-MCP treatment inhibited post-storage volatile production in CA- and air-stored fruit by as much as 95 percent. However, recovery of aroma was delayed significantly in fruit which had been held at 0 °C vs. 2.5 ° C, suggesting aroma volatile synthesis in `Gala' is chilling sensitive.