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  • Author or Editor: Claudia Dussi x
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Fruit color of `Sensation' and `Max' Red Bartlett pears was analyzed once at mid-season and three times during later stages of fruit maturity with a Minolta CR-200b portable colorimeter. Color measurements were taken on sun-exposed and shaded fruit surfaces in three different growing locations in Oregon. Color change is nearly constant over time during fruit maturation. Both cultivars gained red and yellow on sun-exposed fruit surfaces, and lost red but gained yellow on shaded surfaces. `Sensation' gained red on sun-exposed surfaces to a greater extent than did `Max' at all locations. `Max' gained more yellow and lost more red on shaded surfaces than did `Sensation'. Differences between cultivars and locations were greater on shaded than on sun-exposed fruit surfaces. Greatest gain in both red and yellow on sun-exposed surfaces was associated with the warmest growing location. Visually perceived color change with maturity appears to be due both to loss of red on shaded surfaces and gain of yellow on all surfaces.

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The anthocyanin in `Sensation Red Bartlett' pear skin was characterized and quantified, and the effect of light quality on fruit color development was evaluated. Anthocyanin concentration was related to fruit chromaticity values. Pigments were analyzed using high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC). One of two spots detected in the TLC chromatogram did not change color with molybdate sprays, indicating the possible presence of peonidin. HPLC analysis confirmed the presence of a major and a minor pigment, which co-eluted with cyanidin 3-galactoside and peonidin 3-galactoside. Monomeric anthocyanins in the pear skin extract were 6.83 mg/100 g of fruit peel. To study light quality, gelatin filters allowing passage of different wavelengths of-light were attached over the exposed side of `Sensation Red Bartlett' pears 1 month before harvest. Chromaticity was recorded before the filters were attached and after their removal at harvest using the Commission Internationale del'Eclairage (L*, a*, and b*) color space coordinates. Following color measurements, anthocyanin was extracted from individual skin disks. Skin beneath all filters yielded less hue than the control. Wavelengths that transmit above 600 nm had the largest effect on chroma, a*, and b* values. Fruit wrapped in aluminum foil to obscure all light had the highest luminosity. Wavelengths from 400 to 500 nm gave darker, less chromatic, and redder pear fruit. All treatments yielded higher anthocyanin content than the control. There was a tendency toward increased anthocyanin content with longer wavelengths. The simple linear regression of the log anthocyanin content on L* value and (a*/b*) provided an R 2 = 0.41.

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Over-tree sprinkler irrigation cooling treatments were applied to `Sensation Red Bartlett' pear trees during the final 30 days of fruit maturity in 1992 and 1993 when orchard air temperatures were >29 °C. Fruit from cooled trees were more red and less yellow than fruit from noncooled trees, resulting in lower hue values by the middle of the harvestable maturity period in both years of study. In 1992, cooled fruit had a greater portion of the fruit surface covered with red blush than fruit that were not cooled. Fruit firmness decreased more rapidly in fruit from cooled trees than in fruit from noncooled trees, indicating advanced maturity. Accordingly, cooled fruit should be harvested earlier than noncooled fruit to maintain postharvest quality. Differences between cooled and noncooled fruit with respect to hue, surface blush, and rate of firmness loss were more pronounced in a warm season requiring frequent cooling than in a cooler season.

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