Fruit color development in red pears Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/s7526f66w

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  • A fruit color descriptive study was conducted on 'Max' and 'Sensation' Red Bartlett, 'Columbia' and 'Gebhard' Red Anjou, 'Rogue Red', 'Rosired', 'Red Clapp' and 'Cascade' red pear varieties. A parallel comparative study was done to test differences between related red strains. 'Max' was compared with 'Sensation' in three different growing regions: Medford, Hood River high elevation and Hood River low elevation, while 'Columbia' was compared with 'Gebhard' in two locations: Medford and Hood River. The effect of modifying temperature by evaporative cooling and of light quality on color of 'Sensation' Red Bartlett pears were also evaluated. Anthocyanins of red pear skin were characterized and quantified and their concentrations were related to fruit chromaticity values. In all the studies fruit color was measured with a portable tristimulus colorimeter using the Commission Internationale de I'Eclairage color space (L*, a* and b*) coordinates at four times during fruit maturation. Visual percentage of blush was also evaluated. Evaporative cooling was done with overtree sprinkler irrigation. Skin anthocyanins were extracted with acetone, isolated with polyvinylpyrrolidone (PVPP) and recovered in 1% methanolic Hcl. The extract was analyzed using high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC). Monomeric anthocyanin content was determined in an aqueous extract using a pH differential method. To study the effect of light quality on color development, gelatin filters of different spectral transmittance were attached over the exposed side of 'Sensation' pear fruits one month before harvest. Chromaticity was recorded before the filters were placed and at harvest after their removal. Following color measurements, anthocyanins were extracted from individual skin disks. In the descriptive study, every strain presented different color development. Hue, chroma and L* increased with maturity in fruits of all varieties except for 'Rogue Red' and 'Rosired'. 'Rosired' had the biggest change in hue during maturity and 'Cascade' had the smallest. 'Columbia' and 'Gebhard' showed the smallest change in chroma and 'Rogue Red' had the highest gain in L* value. There were high differences in color between exposed and shaded fruit surfaces and at each stage of maturity for every variety. In the variety comparison study various interactions were found among the main factors: growing location, variety, surface of the fruit and stages of maturity. Gain in chroma, hue and L* with maturity was higher in 'Max' than in 'Sensation', higher in Medford than in the other growing regions, and higher on the shaded sides of fruit than on the exposed ones. Increase in chroma, hue and L* value with maturity was higher in Hood River for 'Columbia' than for 'Gebhard', while the opposite was observed in Medford. Shaded fruit surfaces had higher chromaticity values. Evaporative cooling promoted red skin color. However, the increase in coloration may have been due in part to advanced maturity stimulated by the evaporative cooling. HPLC and TLC analyses confirmed the presence of a major and a minor pigment which coeluted with cyanidin 3-galactoside and peonidin 3-galactoside. The average content of anthocyanins in red pear skins was 6.83 mg/100 g of fruit peels. In the light quality study all filters yielded less hue than the control. Wavelengths above 600 nm had the largest effect in chroma. Aluminum wrapped fruit had the highest luminosity. Wavelengths form 400 to 500 nm gave darker, less chromatic and redder pear fruit. All treatments especially longer wavelengths yielded higher anthocyanin content than the control.
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