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- Author or Editor: Dennis P. Murr x
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.
This study evaluated the effects of 1-methylcyclopropene (1-MCP) on ‘Empire’ and ‘Delicious’ apples (Malus ×domestica) in commercial controlled atmosphere (CA) storage for 12 months and in commercial cold storage for 6 months. Apples were harvested and delivered by growers to a local commercial storage facility. Four different grower lots were chosen for each of three ‘Empire’ and two ‘Delicious’ storage rooms. Fruit were treated with 1-MCP (≈0.8–1.0 ppm) for 24 hours, while control fruit samples were held in a similar nearby storage room. After treatment, control samples were placed with matching 1-MCP-treated samples into either CA (2.5% O2 + 2.5% CO2 at 2.2 °C or 0 °C for ‘Empire’ and ‘Delicious’, respectively) or air storage at 0 to 1 °C. Initial maturity was relatively uniform among the grower lots, with internal ethylene concentration (IEC) averaging less than 1 ppm for ‘Empire’ and 2 to 3 ppm for ‘Delicious’. IEC was lower in apples treated with 1-MCP after air (3 or 6 months) or CA (6, 9, or 12 months) storage, but this effect was reduced after a 14-day ripening period at 22 °C, and was less dramatic in fruit from CA than from air storage. Apples treated with 1-MCP were also firmer than non-treated fruit upon removal from air or CA storage, and this difference became greater with increased poststorage time at 22 °C. 1-MCP-treated apples stored in air had higher soluble solids concentration (SSC), while there was no significant effect of 1-MCP on SSC in fruit held in CA. Core browning developed in ‘Empire’ held in air for 6 months or in CA for 9 or 12 months, and in ‘Delicious’ after 9 or 12 months in CA. 1-MCP decreased the incidence of core browning in ‘Empire’, but increased the incidence in ‘Delicious’. There was no significant effect of 1-MCP on the incidence of internal browning and storage rots, which developed in both cultivars.
This study evaluated the effects of 1-methylcyclopropene (1-MCP) concentration (1000 vs. 625 ppb) and treatment delays (3, 7, and 10 days after harvest) on the ripening and incidence of storage disorders in ‘McIntosh’ apples from three harvest times in 2004. Apples were stored in air at 0 °C to 1 °C for 3 and 6 months or in controlled atmosphere (CA) storage at 3 °C for 6 and 9 months. Apples treated with 1-MCP and held in air or CA storage were firmer than those not treated, but this difference in firmness was less with later harvests, more delay before 1-MCP treatment, and longer storage time. Apples treated with 1000 ppb 1-MCP were often firmer than those treated with 625 ppb after 6 months of storage and/or 7 days at 22 °C. Ethylene and carbon dioxide (CO2) production were reduced in apples treated with 1-MCP, especially in fruit from the first harvest and those treated 3 days after harvest. Fruit treated with 1000 ppb 1-MCP showed a slower increase in ethylene production than those treated with 625 ppb during 14 days at 22 °C after storage. CO2 production was the lowest in ‘McIntosh’ apples treated with 1000 ppb 1-MCP 3 days after harvest, but fruit treated with 625 ppb also exhibited lower respiration than those not treated. Storage disorders were most prevalent in ‘McIntosh’ apples stored for 6 months in air at 0 °C to 1 °C, whereas fruit from the first harvest treated with 1-MCP 3 days after harvest developed the fewest disorders. 1-MCP reduced the incidence of superficial scald, flesh browning, core browning, and senescent breakdown, while 1-MCP concentration and treatment delay had varying effects. This research has provided the basis for Canadian registration of SmartFreshSM use on apples at 1000 ppb 1-MCP and for the requirement that treatment be within 3 days of harvest.
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.
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.