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  • Author or Editor: C. Mosjidis x
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Strawberry fruit (Fragaria ×ananassa `Chandler') were evaluated at five different stages of growth and development for changes in the senescence process in fruit tissues. Levels of total antioxidant activity, hydrogen peroxide (H2O2), lipid peroxidation product, malondialdehyde, and ethylene production were determined. Total antioxidant activity (TAA) was measured in terms of in situ antioxidants to scavenge the ABTS.superscript +superscript radical cation. With the progression of ripening and senescence, there was a significant decline in TAA that coincided with increased concentration of H2O2, lipid peroxidation and increased production of ethylene. Our results illustrate that the senescence process in strawberry fruit is associated with the decline of TAA and the potential initiation and accumulation of reactive oxygen species. These results are additionally discussed in terms of potential processes associated with abiotic and biotic environmental stresses. Moreover, although strawberry fruit are typically classified as nonclimacteric, this study illustrates that the free radical mediated senescence process is similar to that of climacteric fruits.

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Low-dose gamma-irradiation is becoming increasingly an attractive viable technology for control of food-borne pathogens and extension of shelf life of fruits and vegetables. Typically, gamma-irradiation treatment appears to transiently stimulate ethylene synthesis in tomato, which appears to be stress associated, and dose dependent (Larrigaudie et al., 199l). We have investigated the effects of gamma-irradiation treatment at doses of 0, 0.5, 0.75, and 1.0 kGy, alone and in combination with water-based chemical treatment for improving the storage of tomato maintained at 20 °C and 95% RH for 20 days of storage. Changes in ethylene, ascorbic acid and total antioxidant content, color, total soluble solids and carbohydrate concentration were examined. Our preliminary results indicate that these treatments are effective in reducing ethylene concentration in storage while providing a means of eliminating foodborne pathogens without adversely affecting tomato quality.

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A prevailing hypothesis indicates that a decrease in vegetative growth and cessation in floral initiation in strawberry in response to changes in photoperiod and temperature may correlate with hormonally induced changes. We investigated changes in endogenous free polyamines in crowns, flowers, leaves, and fruit of springbearing strawberries (Fragaria xananassa cvs. Chandler and Earliglow) in response to varying temperatures to induce flowering. Spermidine was the prominent free amine in crowns. No marked changes of putrescine, spermidine, and spermine were observed in crowns during the transition from vegetative to reproductive growth in either cultivar. In contrast, high levels of free polyamines were noted in young developing tissues such as the most recently initiated leaves, flower buds, and green fruit. When the putrescine synthesis inhibitor difluoromethylonithine (DFMO, 1 mm) was exogenously applied, levels of putrescine, spermidine, and spermine were altered in crown tissues in greenhouse experiments. These findings indicate that free polyamines may potentially be associated with the stimulation of new growth in springbearing strawberries under the present experimental conditions evaluated.

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The relationship between fruit maturation and accumulation of hydrogen peroxide (H2 O2), lipid peroxidation, ethylene (C2 H4) production, antioxidant activity (hydrophilic, lipophilic and total) and the antioxidant enzyme ascorbate peroxidase (APX, EC 1.11.1.11) in fruit pericarp tissue of `Chandler' (Fragaria × ananassa Duch.) strawberry were measured. `Chandler' fruit pericarp maturation and ripening were accompanied by a decline in H2 O2 content early in fruit development followed by a rapid accumulation. An increase in membrane lipid peroxidation (thiobarbituric acid reactive substances, TBARS) coincided with accumulation of H2 O2, which preceded a rise in C2 H4 production. In general, antioxidant activity declined as fruit matured and ripened. APX enzyme activity increased by 2-fold and peaked at the pink stage of development and then gradually declined with ripening. H2 O2 may serve as a signal molecule to initiate the cascade of oxidative processes during maturation and ripening. APX enzyme activity during maturation and ripening was not substantial and thus, may not have a role in alleviating accumulation of H2 O2 and subsequent events related to oxidative senescence in fruit pericarp. To our knowledge, this is the first study to present fractionated antioxidant activities (HAA, LAA and TAA) from strawberry pericarp as assessed by the ABTS∼+ radical cation assay. A fundamental understanding of the mechanisms involved in the senescent related-oxidative changes during strawberry fruit ontogeny in relation to quality and nutrition is discussed.

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