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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.

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H.P. Vasantha Rupasinghe, Gopinadhan Paliyath and Dennis P. Murr

To decipher the relation between α-farnesene metabolism and the development of superficial scald in apples, trans,trans-α-farnesene synthase, the enzyme that catalyzes the conversion of farnesyl pyrophosphate to α-farnesene, was partially purified from skin tissue of `Delicious' apples (Malus ×domestica Borkh.) and characterized. Total and specific activities of the enzyme were higher in the cytosolic fraction than in membrane fractions. α-Farnesene synthase was purified 70-fold from the cytosolic fraction by ion exchange chromatography and gel permeation, and the native molecular weight was estimated to be 108,000. The enzyme had optimal activity at a pH of 5.6 and absolutely required a divalent metal ion such as Mg2+ or Mn2+ for activity. It exhibited allosteric kinetics, S(0.5) for farnesyl pyrophosphate being 84±18 μmol·L-1, and a Hill coefficient (nH) of 2.9, indicating the number of subunits to be two or three. Enzyme activity was highest between 10 and 20 °C, while 50% of the maximal activity was retained at 0 °C. In vivo α-farnesene synthase activity was minimal at harvest, then increased rapidly during 16 weeks storage in air at 0 °C, and decreased during further storage. Activity of α-farnesene synthase, α-farnesene content, and conjugated triene alcohol (the putative scald-causing oxidation product of α-farnesene) content in skin tissue were not correlated to the inherent nature of scald susceptibility or resistance in 11 apple cultivars tested.

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Vicky W. Lee, H.P. Vasantha Rupasinghe* and Chung-Ja Jackson

Apples are excellent sources of dietary phenolics, in particular flavonoids and chlorogenic acid, which are potent antioxidants that may play important roles in the prevention of chronic diseases. This study investigated the major phenolics profiles of apple fruit in relation to (1) the distribution among 8 Ontario-grown cultivars, (2) the different fruit parts, and (3) the effect of processing of fresh-cuts. In addition, total antioxidant capacity (TAC) and total phenols content (TPC) were measured in apples by spectrophotometric assays. Flavonoids and chlorogenic acid were quantified using HPLC/PDA. Vitamin C was quantified using HPLC/Fluorescence. TAC, TPC and flavonoids levels were the highest in Honey Crisp and Delicious, moderate in Idared, Spartan, Granny Smith, and Cortland, and the lowest in Crispin and Empire. Apple peel contained 2 to 10-fold higher TAC, TPC and total of 10 major phenolics than that of core and flesh indicating peeling of apples during processing could reduced significantly the nutritional quality of fresh-cut apples. Dihydrochalcone (phloridzin) and chlorogenic acid levels were 2 to 21-fold higher in apple core than skin and flesh. TAC levels and vitamin C contents could be increased up to 3-fold and 14 to 20-fold, respectively by the post-cut dipping treatment with an ascorbic acid-based antioxidant formula. The phenolic profiles of sliced apples were stable up to 21 days at 4°C.

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

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.

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

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.

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Cindy Campeau, John T.A. Proctor, Chung-Ja C. Jackson and H.P. Vasantha Rupasinghe

Rusty root is a major problem in ginseng production worldwide as it reduces root quality. Full characterization of rusty root is unavailable, and necessary for development of effective control measures. A comparison of phenolics, antioxidants, ginsenosides, and mineral nutrient content of rusted and non-rusted tissue from disease-free roots is reported. Periderm and adjacent tissues of 4-year-old North American ginseng roots (Panax quinquefolius L.) had a total phenolic content of 3.05 mg·g-1 dry weight (as gallic acid equivalents), which was increased 53% by rust-spotting. Antioxidant activity increased with phenolic content and was 33% higher (3.6 vs. 2.7 mg·g-1 dry weight as ascorbic acid equivalents) in rust-spotted tissue. Total ginsenoside content was higher (139.1 vs. 119.4 mg·g-1) in healthy than in rust-spotted tissue, the latter reflecting a significant decrease in four of the major ginsenosides (Rb2, Rc, Rd, and Re). The Rg group was higher (38.0 vs. 29.9 mg·g-1) in healthy than in rust-spotted tissue. The mineral elements N, P, Ca, Mg, Zn, Mn, and Fe were higher, and K lower (21%) in rust-spotted tissue than in healthy tissue.