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D. Mark Hodges and Gene E. Lester

The consumption of netted muskmelons (Cucumis melo L. Reticulatus group) has raised health concerns due to pathogenic bacteria attaching to sites on the netted rind inaccessible to sanitation. The purpose of this study was to compare 1) the enzymic and nonenzymic antioxidant capacity between representative cultivars of netted muskmelon and both green- and orange-fleshed honey dew muskmelons during storage for 17 days and 2) levels of non-nutrient phytochemicals between these genotypes in consideration of ultimately substituting netted orange-fleshed with non-netted orange-fleshed muskmelon. Netted muskmelon (`Cruiser'), green-fleshed (`Honey Brew'), and orange-fleshed (`Orange Dew') muskmelons were harvested in Texas at the beginning (21 May) and at the end (11 June) of the production season in 2004. Fruit were analyzed immediately (day 0) or stored simulating retail conditions for 7 or 14 days at 7 °C and 95% ± 2% relative humidity plus 3 days at 21 °C. Both `Orange Dew' and `Honey Brew' non-netted cultivars evinced similar and less lipid peroxidation, and hence postharvest senescence, during the 17-day storage period than the netted muskmelon `Cruiser'. In comparison with `Cruiser', `Orange Dew' generally exhibited higher concentrations of ß-carotene and phenolics and, with few exceptions, higher activities of the antioxidant enzymes ascorbate peroxidase (AsPX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), catalase (CAT), guaiacol peroxidase (POX), and superoxide dismutase (SOD). Higher AsPX and SOD activities in both `Orange Dew' and `Honey Brew' appear to confer a greater resistance to lipid peroxidation in these muskmelon genotypes than to the netted `Cruiser'. `Orange Dew' also appears to be a healthier food choice not only due to its lack of a netted rind which could potentially harbour human illness-related pathogens, but also that it is superior to both `Cruiser' and `Honey Brew' in overall beta-carotene and phenolic levels.

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D. Mark Hodges and Charles F. Forney

Rapidly declining levels of ascorbate (vitamin C) have been associated with advancing senescence and postharvest quality loss in spinach (Spinacia oleracea L.). To further explore the association between ascorbate metabolism and senescence, two cultivars of spinach previously shown to differ in their postharvest senescence rates were grown under controlled conditions (18 °C, 14 light: 10 dark photocycle) and harvested 6 weeks after planting. Detached leaves of `Spokane F1' (relatively fast senescence rate) and `BJ412 Sponsor'(relatively slow senescence rate) were bagged and placed in the dark at 10 °C. Samples were removed on days 0, 7, 14, 21, and 28, and analyzed for activities of L-galactono-γ-lactone dehydrogenase (GLDH), ascorbate peroxidase (ASPX), ascorbate oxidase (AAO), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR), and levels of ascorbate [reduced (AsA) and oxidized (DHA)] and malondialdehyde (MDA) (estimator of lipid peroxidation). Oxidative stress, as estimated by MDA levels, steadily increased in both spinach cultivars during storage, but increased more in `Spokane'than in `Sponsor'. GLDH activities peaked on day 14 for both cultivars and leveled off thereafter, while activities of ASPX, DHAR, and MDHAR declined during storage. ASPX activities were lower in `Spokane'than in `Sponsor'after day 21. No difference in AAO activities was noted between `Sponsor'and `Spokane'during storage. Total ascorbate concentrations declined in both cultivars on day 14 after which no further decreases were noted, while DHA/AsA ratios increased during storage. Early in the storage regime (days 0 and 7), ascorbate levels were lower in `Spokane'than in `Sponsor. GLDH activities may have increased as part of a strategy to maintain the ascorbate pool during escalating oxidative stress. However, decreased levels of ascorbate suggests that, even though ascorbate biosynthesis was increased, ascorbate was being degraded, possibly through hydrolysis of DHA to 2,3-diketogulonate. Initially lower levels of ascorbate (days 0 and 7) and lower activities of ASPX (day 28) in `Spokane' may have resulted in comparatively greater susceptibility of this cultivar to oxidative stress than `Sponsor'.

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Gene E. Lester, Robert A. Saftner and D. Mark Hodges

Orange-fleshed honey dew (Cucumis melo L., Inodorus group) fruit are known for having superior food-safety, food-quality, and fruit-marketability attributes compared with orange-fleshed netted muskmelon (C. melo, Reticulatus group) and to green-fleshed honey dew (C. melo, Inodorus group) fruit. However, little is known about the production market attributes and postharvest quality comparisons of the leading orange-fleshed honey dew cultivars. Five orange-fleshed honey dew genotypes (‘Honey Gold’, ‘Orange Delight’, ‘Orange Dew’, ‘Temptation’, and a breeding line) were glasshouse-grown in both fall and spring, harvested at abscission (full-slip), and compared after storage for 3–24 days in air at 5 or 10 °C. Fruit maturity (full-slip) was between 31 and 38 days after anthesis, with maturation dependent on genotype. Days to maturity were slightly longer in the fall than in the spring. Fruit size (number of fruit per standard commercial shipping box) was between four and six fruit per box. ‘Orange Dew’ consistently had the smallest fruit (six per box), and the breeding line had the largest (four per box). ‘Orange Delight’ and ‘Orange Dew’ had the fewest whole-fruit disorders and the highest percentage of marketable fruit at harvest and following 24 days of storage at 5 or 10 °C. ‘Orange Delight’, ‘Orange Dew’, and the breeding line consistently had a more yellow peel, whereas ‘Honey Gold’ and ‘Temptation’ fruit peels had a more greenish hue. Whole-fruit firmness was 10–25 N among the cultivars and 24–35 N for the breeding line. Internal-fruit disorders, percentage marketability, and mesocarp (pulp) firmness reflected each genotype's whole-fruit attributes. ‘Orange Delight’ and ‘Orange Dew’ fruit consistently had among the highest soluble solids concentration and relative sweetness ratings, and their pulp had a more intense orange hue and lower lightness than those of the other genotypes. After 24 days of storage, ‘Orange Delight’ and ‘Orange Dew’ maintained their higher sweetness and more orange hue in both spring and fall harvests; however, depending on harvest, they were not always significantly sweeter or more orange-hued than some of the other genotypes. Our results indicate that orange-fleshed honey dew fruit are a promising new melon type suitable as a substitute for orange-fleshed netted muskmelon fruit not only for food-safety issues but also for overall marketable quality.

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D. Mark Hodges, Wendy V. Wismer and Charles F. Forney

The responses of certain antioxidants in detached leaves of two cultivars of spinach (Spinacia oleracea L.) differing in their senescence rates were assessed during storage in order to explore the significance of these antioxidants in senescence regulation and dynamics. To identify spinach cultivars differing in their senescence rates, 10 cultivars were grown in field plots, harvested at maturity, and their leaves detached and stored at 10 °C in the dark. At the point of harvest (d 0) and on d 5, 8, 12, and 15, samples were analyzed for lipid peroxidation (MDA), chlorophyll loss, and electrolyte leakage. The cultivars were also grown in laboratory growth chambers to corroborate field results. Two cultivars that were consistently identified as having relatively high (Spokane F1) and low (BJ 412 Sponsor) senescence rates were grown in growth chambers for 45 d, harvested at maturity, and their leaves detached and stored as above. At the point of harvest (d 0) and on d 4, 8, 12, 16, and 20, samples were analyzed for (i) activities of ascorbate peroxidase (ASPX; EC 1.11.1.11), catalase (CAT; EC 1.11.1.6), and superoxide dismutase (SOD; EC 1.15.1.1), and (ii) concentrations of MDA, total ascorbate, reduced ascorbate (AsA), oxidized ascorbate (DAsA), total glutathione, reduced glutathione (GSH) and oxidized glutathione (GSSG). Although MDA accumulated in leaves of both cultivars concomitant with time after detachment, levels became significantly higher in Spokane. Activities of ASPX declined in Spokane leaves following detachment but activities of SOD and levels of glutathione increased in this cultivar. GSH/GSSG increased in `Sponsor', but dramatically more so in `Spokane'. Ascorbate concentrations did not diminish in leaves of `Spokane' to the degree that they did in `Sponsor' tissue. DAsA/AsA values did not decrease in `Spokane' leaves following detachment, though they did in those of `Sponsor'. It is argued that declining activities of ASPX and levels of ascorbate and increasing activities of SOD manifested in accumulation of hydrogen peroxide in Spokane, leading to a greater potential for lipid peroxidation in this variety than for Sponsor. SOD activities and glutathione levels may have increased as a result of elevated oxidative stress in Spokane. Increased hydrogen peroxide accumulation in `Spokane' relative to `Sponsor' may have contributed to an increased rate of senescence in the leaves of this cultivar.

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D. Mark Hodges, Charles F. Forney and Wendy Wismer

The degree of damage that may occur through harvesting and packing represents one of the major factors that can affect quality of fresh-cut produce. The purpose of this study was to examine the effects of different steps in a representative fresh-cut processing line on storage quality of spinach (Spinacia oleracea L.). To this end, spinach leaves were removed at successive points on the line: 1) before entry into the line (control); 2) after a shaking procedure but before initial rinsing with 10 °C water + 5 mg·L-1 chlorine dioxide; 3) after centrifugal drying; and 4) after commercial packaging. After removal from the different points in the line, the spinach samples were stored at 10 °C for 16 days, during which time malondialdehyde (MDA) concentration (lipid peroxidation assay), electrolyte leakage (membrane leakiness), chlorophyll content (a, b, and total), and color attributes (L, saturation, hue angle) were measured. Both lipid peroxidation and electrolyte leakage increased with time of storage and with stage of procesing. Electrolyte leakage increased most in material removed after the shaking procedure, but prior to hydrocooling. Overall total chlorophyll loss during storage did not change with time of removal from the processing line, although overall chlorophyll b content decreased in stored material 8 days following centrifugal drying and packaging. A more rapid loss in chlorophyll a relative to chlorophyll b over the first 8 days of storage was reflected in hue angle measurements regardless of the point of removal. The processing line under study, thus had both beneficial and detrimental effects on storage quality of spinach. Detrimental effects associated with centrifugal drying and packaging procedures could be modified to improve quality.

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D. Mark Hodges, Charles F. Forney and Wendy V. Wismer

The objective of this study was to assess responses of certain antioxidants in harvested leaves of selected cultivars of spinach (Spinacia oleracea L.) differing in postharvest senescence rates in order to explore the significance of these antioxidants in postharvest senescence regulation and dynamics. Ten cultivars were grown in both field plots and laboratory growth chambers, harvested at maturity, and their leaves detached and stored at 10 °C in the dark. Following postharvest analysis, two cultivars were identified consistently as having relatively high (`Spokane F1') and low (`BJ 412 Sponsor') postharvest senescence rates. These two cultivars were then grown in a growth chamber for 45 days and their leaves detached and stored as above. At the point of harvest (day 0) and on days 4, 8, 12, 16, and 20, samples were analyzed for activities of ascorbate peroxidase (ASPX; EC 1.11.1.11), catalase (CAT; EC 1.11.1.6), and superoxide dismutase (SOD; EC 1.15.1.1), and (ii) concentrations of malondialdehyde (MDA, an indicator of lipid peroxidation), total ascorbate, reduced ascorbate (AsA), oxidized ascorbate (DAsA), total glutathione, reduced glutathione (GSH), and oxidized glutathione (GSSG). Although MDA accumulated in leaves of both cultivars concomitant with time after detachment, levels became significantly higher in `Spokane F1'. It is argued that declining activities of ASPX and levels of ascorbate and increasing activities of SOD manifested in accumulation of hydrogen peroxide in `Spokane F1', leading to a greater potential for lipid peroxidation in this cultivar than for `BJ 412 Sponsor'. SOD activities and glutathione levels may have increased as a result of elevated oxidative stress in `Spokane F1'. Increased hydrogen peroxide accumulation in `Spokane F1' relative to `BJ 412 Sponsor' may have contributed to an increased rate of senescence in the harvested leaves of this cultivar.

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D. Mark Hodges, Gene E. Lester, Robert D. Meyer, Vivian E. Willmets and Michele L. Elliot

Consumption of phytochemicals has been associated with reduced risks of human health dysfunctions such as cancers and heart disease. Such information has led to increased sales of fruits and vegetables. For example, in the United States, an estimated 23% increase in melon consumption (up to 13.2 lbs/capita/annum) has been recorded over 16 years. However, some health issues have been attributed to cantaloupe due to bacteria such as Salmonella attaching to inaccessible sites, such as the rind netting. Honeydew melons do not have a netted rind. The purpose of this study was to compare concentrations of antioxidants between cantaloupe and both green- and orange-fleshed honeydew melons during 14 days of storage to determine if orange-fleshed honeydew melon would represent a feasible alterative to cantaloupe to the increasingly health/food safety-conscious consumer. Cantaloupe (`Cruiser'; C), green-fleshed Honeydew (`HoneyBrew'; HB), and orange-fleshed Honeydew (`OrangeDew'; OD) melons were harvested in Texas at the beginning and at the end of the production season. β-carotene content was highest in OD, followed by C; no β-carotene was detected in HB. β-carotene levels did not change during storage. Phenolic levels increased in all three melon species during storage, whereas total ascorbate content declined in OD and in early harvest HB. Ascorbate peroxidase activities were lowest in OD, perhaps due to the lower ascorbate levels; little difference between the melon species in activities of the other ascorbate-associated enzymes were observed. Based on the phytochemicals measured in this study, choosing non-netted OD over netted C in order to reduce potential exposure to pathogens would not represent a less healthy food choice.

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D. Mark Hodges, Gene E. Lester, Kathleen D. Munro and Peter M.A. Toivonen