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- Author or Editor: Jingtair Siriphanich x
Immature and mature durian (Durio zibethinus Murr.) fruit dehiscence was studied. Fruit were stored at 27C and 65% or 95% relative humidity, with or without 24-hour exposure to 100 ppm ethylene. Low relative humidity and ethylene increased fruit dehiscence. Spraying fruit with 100 ppm GA3 delayed dehiscence but allowed pulp ripening to continue. The plant-growth regulators IBA; 2,4-D; 2,4,5-T; BAP; daminozide; and mepiquat chloride had no consistent effects on fruit dehiscence. Various coating materials delayed dehiscence and ripening; a sucrose fatty acid ester at 1% concentration gave the best result. All coating materials reduced weight loss 7% to 14% below that of the control fruit. Fruit coated with the sucrose fatty acid ester and 100% apple wax had higher internal CO2 levels than fruit coated with any other coating. Ethylene is more important in durian fruit dehiscence than weight loss. Chemical names used: 3-indolebutyric acid (IBA); 2,4-dichlorophenoxyacetic acid (2,4-D); 2,4,5-trichlorophenoxyacetic acid (2,4,5-T); 6-benzylaminopurine (BAP); succinic acid-2,2-dimethyl hydrazide (daminozide); 1,1-dimethyl-piperidinium chloride (mepiquat chloride); gibberellic acid (GA3).
Abstract
‘Climax’ lettuce (Lactuca sativa L.) exhibited more severe CO2 injury symptoms than ‘Salinas’ and ‘Winterhaven’ lettuce when exposed at 20°C to air for 1 day following treatment for 6 days at 0° with 15% CO2 in air. All 3 cultivars, however, had similar decreases as revealed by NMR analysis, of about 0.4 and 0.1 pH units in the cytoplasm and vacuole, respectively. This result indicates that variation in the buffering capacity was not related to differences in susceptibility to CO2 injury among these cultivars. Although CO2 reduced pH, it also reduced titratable acidity of lettuce tissue. This change resulted in a higher pH when the lettuce was moved to air. Exposure of lettuce at 0° to light reduced CO2 injury by about 50% relative to tissue kept in the dark. Lettuce tissue kept in air had a higher glucose-6-phosphate content than the CO2-treated lettuce. A hypothesis regarding alternate energy supply mechanisms for resistance of lettuce tissue to elevated CO2 injury is discussed.
Abstract
An atmosphere of air + 15% CO2 caused CO2 injury in lettuce (Lactuca sativa L.) in about 10 days at 0°C. However, subsequent removal of CO2 was necessary for the brown stain symptoms to develop. Under CO2 treatment, phenylalanine ammonia lyase (PAL) was induced and its activity correlated well with the development of the injury. Nevertheless, PAL activity did not seem responsible for the differences in susceptibility to CO2 injury among the 3 lettuce cultivars included in this study. Prevention of the development of brown stain symptoms by CO2 probably was due to its inhibition of phenolics production and the inhibition of polyphenol oxidase activity.
Abstract
An atmosphere of air + 15% CO2 prevented the development of cinnamic acid-4-hydroxylase in both lettuce (Lactuca sativa L.) and potato (Solanum tuberosum L.) tissues. Subsequent removal of CO2 did not allow the enzyme development to proceed, whereas total phenolic content increased and browning became visible. In addition, CO2 did not have an inhibitory effect on the enzyme, prepared from potato tissue, per se. Thus, the effects of CO2 on inhibition of lettuce tissue browning does not appear to involve this enzyme. No tyrosine ammonia lyase activity was found in lettuce tissue.
The effect of naturally occurring volatile compounds on decay and antioxidant activities in fresh-cut papayas (Carica papaya L.) was studied. Exposure to methyl jasmonate (MJ), methyl salicylate (MS) or allyl isothiocyanate (AITC) substantially delayed the onset and reduced the severity of decay during and after storage at 5 °C. Treatment with tea tree oil (TTO) or ethanol (ETOH) was also effective in retarding decay, but to a lesser extent. No beneficial effect was obtained with the use of vinegar vapor. MJ and MS increased oxygen radical absorbance capacity and elevated the activities of several antioxidant enzymes, including glutathione reductase, glutathione peroxidase, guaiacol peroxidase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and superoxide dismutase. The nonenzyme components in the ascorbate-glutathione cycle were also increased by MJ and MS treatments, including ascorbate and glutathione. It is possible that MJ and MS treatments enhanced the antioxidant system and increased the resistance of tissue to decay. However, while AITC also suppressed the development of decay in papaya slices, it had little effect on antioxidant levels and antioxidant enzyme activities. Apparently, AITC exerted its effect through different mechanisms. Studies are in progress to determine if AITC inhibits decay directly via its antimicrobial properties.