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  • Author or Editor: Dangyang Ke x
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Consumer acceptance of sensory quality was significantly correlated (P = 0.05) with overall eating quality of tomatoes (Lycopersicon esculentum Mill.) determined by a trained taste panel. The overall eating quality was partitioned into three flavor components (sweetness, sourness, and aroma) and internal texture. Relationships between the sensory flavor components and concentrations of several chemical compounds were analyzed in tomatoes of eleven varieties within a range of acceptable texture. Sweetness was significantly correlated with total sugar concentration and overall flavor at P = 0.01 and 0.001. High concentrations of two ketone volatiles (6-methyl-5-hepten-2-one and 1-penten-3-one) were significantly correlated with aroma and overall flavor at P = 0.05 to 0.001. This study indicates that positive tomato flavor may be characterized by high sweetness, moderate acidity, and high concentrations of certain ketone volatiles.

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Selected cultivars of several fruit species were exposed to 0.25% or 0.02% O2 at 0, 5, or 10C for short durations to investigate the potential of these treatments as quarantine procedures for postharvest insect control. Beneficial effects of such low O2 treatments included inhibition or delay of ripening processes as indicated by reduction in respiration and ethylene production rates, retardation of skin color changes and flesh softening, and maintenance of titratable acidity. While appearance was not adversely influenced by the short-term low O2 treatments, the development of alcoholic off-flavor was the most important detrimental effect, which limited the tolerance of fresh fruits to low-O2 atmospheres. Ethanol content and flavor score of the fruits had a logarithmic relationship. The threshold ethanol concentration associated with off-flavor detection (EO) increased with SSC of the commodity at the ripe stage, and it could be estimated using the following formula (Log EO)/SSC = 0.228. Using SSC of ripe fruits and average ethanol accumulation rate per day (V) from each low O2 treatment, the tolerance limit (Tl) of fruits to low O atmospheres could be predicted as follows: Tl = EO/E = 1 00.228 SSC2/V.E

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Abstract

In the article “Effects of Calcium and Auxin on Russet Spotting and Phenylalanine Ammonialyase Activity in Iceberg Lettuce” by Dangyang Ke and Mikal E. Saltveit, Jr. (HortScience 21:1169–1171, Oct. 1986), Dangyang Ke's name was spelled incorrectly.

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Fruits of peach (Prunus persica L., cv. `Fairtime') and plum (Prunus domestica L., cv. `Angeleno') were kept in air and in 0.25% or 0.02% O2 at 0, 5, or 10°C for 3 to 40 days to study the effects of temperatures and insecticidal low O2 atmospheres on their physiological responses and quality attributes. Exposure to low O2 atmospheres reduced respiration and ethylene production rates of the stone fruits. The low O2 treatments retarded color change and flesh softening of plums and maintained acidity of peaches. Exposure to the low O2 atmospheres also delayed incidence and reduced severity of internal breakdown (chilling injury) and decay of the peaches at 5°C and, therefore, maintained both external and internal appearance qualities of the fruits longer than those kept in air. The most important limiting factor for fruit tolerance to insecticidal low O2 atmospheres was development of alcoholic off-flavor which was associated with accumulation of ethanol and acetaldehyde in the fruits. The peaches and plums could tolerate exposures to the low O2 atmospheres for 9 to 40 days, depending on the temperature and O2 level used. These results suggest that stone fruits are quite tolerant to insecticidal low O2 atmospheres.

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A 1.5% O2 atmosphere, relative to normal air, dramatically inhibited ethylene-induced russet spot development, PAL, and ionically bound POD, and ionicaliy bound IAA oxidase activities and reduced soluble phenolic content in stored iceberg lettuce (Lactuca sativa L.). Low O2 also inhibited eythylene production and respiration. Polyphenol oxidase activity was slightly inhibited by low O2. The results suggest that low O2 inhibition of ethylene action and attendant effects on phenolic metabolism and IAA oxidase activity may be responsible for inhibition of russet spotting by 1.5% O2. Chemical names used: indole-3-acetic acid (IAA); phenylalanine ammonia-lyase (PAL); peroxidase (POD); polyphenol oxidase (PPO).

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Controlled atmospheres containing air + 11% CO2 caused tissue injury and induced phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) activity in iceberg lettuce (Lactuca sativa L.) midrib tissue. Injury symptoms included brown stain (browning of epidermal tissue) and sunken epidermal areas (pitting) a few millimeters in diameter. Pitting occurred in high-CO2 atmospheres at 5C with no increase in phenolic content, but browning did not develop until the tissue had been transferred to air at 25C. Browning developed within several hours of transfer to air and the degree of browning was correlated with the soluble phenolic content. The oxidation of soluble phenolic compounds to brown substances by polyphenol oxidase (PPO, EC 1.10.3.2) could account for tissue browning. Lignification was associated with cell wall thickening in discolored tissue and was accompanied by an increase in ionically bound and soluble peroxidase (POD, EC 1.11.1.7) activities. Exposure of tissue to elevated CO2 increased ionically bound indoleacetic acid (IAA) oxidase activity, but reduced soluble IAA oxidase activity. Application of an aqueous solution of 1.0 mm IAA to the tissue before treatment did not significantly reduce browning. Lettuce tissue exposed to 1.5% O2 + 11% CO2 had reduced PAL activity and lower soluble phenolic content than lettuce exposed to air + 11% CO2. Depending on the sensitivity of the lettuce tissue to CO2 injury, low-O2 atmospheres either reduced or slightly retarded browning induced by 11% CO2.

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Abstract

Leaf midrib tissue from six cultivars of iceberg lettuce (Lactuca sativa L.) was excised from 20- to 100-day-old plants and tested at 5C for russet spotting (RS) susceptibility under 10 μl ethylene/liter. There was no RS development in tissue excised from 20-day-old plants from any of the six cultivars. RS first developed in tissue from 50-day-old plants and tended to be more severe in tissue excised from older plants. ‘Winter Haven’ and ‘Salinas’ were most susceptible, while ‘Calmar’ was most resistant to RS; ‘Climax’, ‘El Toro’, and ‘Sea Green’ were moderately susceptible. Phenylalanine ammonia-lyase activity in the six cultivars at different developmental stages correlated with their degree of RS development. For ‘Winter Haven’, the increase in ionically bound POD and IAA oxidase activity, but not PPO activity, was associated with the increase in RS score during plant development. ‘Winter Haven’ tissue had much higher ionically bound peroxidase and IAA oxidase activities than ‘Calmar’ tissue from 100-day-old plants. Chemical names used: indole-3-acetic acid (IAA), phenylalanine ammonia-lyase (PAL), peroxidase (POD), polyphenol oxidase (PPO).

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Fruits of `Bing' cherry (Prunus avium L.), `Red Jim' nectarine (Prunuspersica L.), `Angeleno' plum (Prunus salicina, L.), `Yellow Newtown' and `Granny Smith' apples (Malus domestica Borkh.), and `20th Century' pear (Pyrus serotina L.) were treated with 0.25% or 0.02% O2 (balance N2) at 0, 5, or 10C to study the effects of these insecticidal low-O2 atmospheres on their postharvest physiology and quality attributes. Development of alcoholic off-flavor was associated with ethanol accumulation, which was the most common and important detrimental effect that limited fruit tolerance to low O2. Relatively higher storage temperature (T), higher respiration rate (R), and greater resistance to gas diffusion (r) enhanced while relatively higher O2 concentration (C) and higher soluble solids concentration (SSC) reduced off-flavor development. Using a SAS computer program to do multiple regression analysis with T, C, R, r, and SSC as variables, models were developed for prediction of fruit tolerance to insecticidal low-O, atmospheres. Comparison of fruit tolerances and published information on the times required to completely kill specific insects by O2 levels at or below 1% suggests that low-O2 atmospheres have a good potential for use as postharvest quarantine treatments for some fruits.

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`Valencia' oranges [Citrus sinensis (L.) Osbeck] tolerated up to 20 days of exposure to 0.5%, 0.25%, or 0.02% O2, at 5 or 10C followed by holding in air at 5C for 7 days without any detrimental effects on external and internal appearance. Oranges stored in 0.5%, 0.25%, or 0.02% O2 had lower respiration rates, but higher resistance to CO, diffusion and higher ethanol evolution rates than those stored in air at 10C. Similar, but less pronounced, effects of the low O2 atmospheres were observed at O and SC. Respiration rates, internal CO2 concentrations, and ethanol evolution rates were generally higher at 10C than at 0C, while resistance to CO2 diffusion was lower at the higher temperature. `Valencia' oranges kept in 60% CO2 at 5C for 5 to 14 days followed by holding in air at 5C for 7 days developed slight to severe injury that was characterized by skin browning and lowered external appearance scores. Juice color, soluble solids content, pH, titratable acidity, and ascorbic acid content were not significantly influenced by either the low O2 or the high CO2 treatments. However, these treatments increased ethanol and acetaldehyde contents, which correlated with the decrease in flavor score of the fruits. Ethanol content of the oranges transferred to air following low 02 treatment correlated with CO2 production rate of the fruits at the transfer temperature and was related to ethanol evolution and probably production rates after the transfer.

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The tolerances (based on time before detection of off-flavor) of nectarine and peach cultivars to an insecticidal controlled atmosphere of 0.25% O2 (balance N2) at 20C were 2.8, 4.0, 4.0, 4.4, 5.1, and 5.3 days for `John Henry' peaches, `Fantasia' nectarines, `Five Red' peaches, `O'Henry' peaches, `Royal Giant' nectarines, and `Flamekist' nectarines, respectively. The greater sensitivity of `John Henry' peaches to low O2 stress was associated with a higher respiration rate; faster accumulation rates of acetaldehyde, ethanol, and ethyl acetate; and a more mature and larger fruit. The tolerances of `Fairtime' peaches to 0.21% O2 + 99% CO2 at 20C, 0.21 O2 + 99% CO2 at 0C, and 0.21% O2 at 20C were 3.8, 5.0, and 6.0 days respectively. There was a good correlation between tolerance of nectarines and peaches to insecticidal atmospheres and the accumulation rates of acetaldehyde (r=-0.94, p<0.01) and ethanol (r=-0.88, p,0.01).

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