Effects of sunlight or shade on maturity and optical density in blueberries

Abstract

Sensing of maturity in blueberries (Vaccinium darrowi L.) using optical density measurements has long been known and used by researchers. This past year a large sample of berries (540) were visually selected with six levels of maturity; Green, White, Red, Just-Ripe, Ripe, and Over-Ripe. Subsequently, spectrographs of individual berries were obtained from about 400 nm to 900 nm. Each berry was chemically assayed for soluble solids (SS), pH, and titratable acidity (Acids). One interesting observation was that the SS/Acids ratios within each of the six carefully selected levels of maturity varied greatly and overlapped between the maturity categories. This study was initiated by one primary question. Is there an effect on the SS/Acids ratio of an individual berry if the berry is allowed to mature in either the presence or absence of sunlight? A secondary issue of investigation was: If there is a sun/shade effect on a berry's SS/Acids ratio, can this effect be observed by measuring the optical density ratio at 740 and 800 nm? Results of 38 sun and 40 shade berries (Cultivars, 'NC 3103' and 'NC 3104') had mean SS/Acids ratios of 30.9 and 31.5, respectively, and were in the same (α = 0.05) Duncan's multiple range grouping. Results of 57 'NC 3103' and 21 'NC 3104' berries had mean SS/Acids ratios of 35.6 and 19.3, respectively, and were in different (α = 0.05) Duncan's multiple range groupings. Correlation coefficients between the SS/Acids ratios and the optical density ratio ranged from -0.88 < -0.66 for shade berries and -0.84 < -0.78 for sun berries, depending upon the optical orientation of the individual berry. © 2004 by The Haworth Press, Inc. All rights reserved.