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Dan D. MacLean and D. Scott NeSmith

A postharvest 1-methylcyclopropene (1-MCP) treatment was evaluated for its ability to maintain firmness and delay the ripening of rabbiteye blueberries. Three cultivars, Austin, Brightwell, and Premier, were harvested by hand from the UGA Alapaha Blueberry Farm and treated overnight with 1 μL·L−1 1-MCP as field heat was being removed [0 to 1 °C, 90% to 95% relative humidity (RH)]. Fruit were evaluated for firmness, total soluble solids (TSS), total acidity (TA), ethylene production, and other quality attributes at 0, 1, and 2 weeks after harvest as well as 1 or 4 days post-removal evaluations at room temperature (≈21 °C). In general, the 1-MCP treatment resulted in the stimulation of ethylene production in all three cultivars but had minimal effect on TSS and TA content. Furthermore, the treatment resulted in an accelerated loss of firmness in ‘Brightwell’. The lack of inhibition of fruit ripening likely related to the fact that blueberries were harvested, and subsequently treated with 1-MCP, at a post-climacteric stage of development. Based on current results, more information is required regarding ethylene production during rabbiteye blueberry fruit maturation before establishing a 1-MCP treatment recommendation for use by the rabbiteye blueberry industry.

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Dan D. MacLean*, Dennis P. Murr, and Jennifer R. DeEll

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.

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Dan D. MacLean, Dennis P. Murr, Jennifer R. DeEll, and Eugene Kupferman

The ethylene antagonist 1-methylcyclopropene (1-MCP) was investigated for its potential impact on the transcription of key flavonoid biosynthetic (PAL and CHS) and ethylene perception (ERS1) genes during the postharvest storage of pear (Pyrus × communis L.). Optimally harvested red and green `d'Anjou' fruit were treated with 1 μL·L-1 1-MCP for 24 h at 0 °C to 1 °C, and subsequently placed in cold storage (0–1 °C, 90–95% RH). Fruit were removed every 21 days for 126 days, and evaluated for firmness, TSS, and ethylene and volatile production for up to 10 days (≈21 °C). Tissue samples were collected for Northern blot analysis and determination of flavonoid and chlorogenic acid content. PAL content increased during the 1-week simulated marketing period irrespective of storage duration, which coincided with an increase in respiration and ethylene content. Although it was still detectable, total PAL content was dramatically reduced by the 1-MCP treatment. CHS was abundant immediately after harvest and after removal from storage, but declined rapidly thereafter, and was not detectable after 1 week at room temperature. The 1-MCP treatment further exacerbated this decreasing trend in CHS content. ERS1 content appears to be stable throughout storage and the simulated marketing period, with levels lower in 1-MCP-treated fruit. These results suggest that 1-MCP significantly inhibits the transcription of key flavonoid and ethylene regulatory enzymes, possibly compromising the nutraceutical content of pear fruit. The increase in PAL with the concomitant decrease of CHS after removal from storage suggests a diversion of carbon from flavonoid compounds into simple phenols, such as chlorogenic acid.