Reflectance spectral features and non-destructive estimation of chlorophyll, carotenoid and anthocyanin content in apple fruit

Abstract

Fruit reflectance spectra of five apple (Malus domestica Borkh.) cultivars (Zhigulevskoe, Antonovka, Granny Smith, Golden Delicious and Renet Simirenko) with a wide range of peel pigment (chlorophylls a and b, carotenoids and anthocyanins) content have been studied to develop non-destructive techniques for pigment assessment. In addition to chlorophylls, positions of in vivo absorption maxima were established for carotenoids (480, 455 and a shoulder at 425 nm) and for anthocyanins (near 550 nm). In anthocyanin-free fruit, a close relationship between reflectance at 550 nm (R550) and 700 nm (R700) has been found (r2>0.95). In fruit with chlorophyll content more than 5 nmol/cm2, the reflectance near 678 nm was insensitive to a variation in chlorophylls, whereas, reflectance in the bands 550–650 nm and 690–705 nm remained sensitive to chlorophyll content in a wide range of its variation. The reflectance ratios, R800/R700 and R800/R640, were directly proportional to total chlorophyll content ranging from 0.4 to 11 nmol/cm2 (r2>0.93). The reflectance in the band 520–530 nm was found to be dependent mostly on carotenoids absorption. The index R800(1/R520−1/R700) was suggested for estimation of carotenoid content in the range 0.6–4.5 nmol/cm2. The index for assessment of a carotenoid/chlorophyll ratio was proposed in the form, (R480−R678)/R800. Reflectance in the green region of the spectrum proved to be sensitive to anthocyanin content. The index R800(1/R550−1/R700) was developed to estimate anthocyanin content in peel ranging from 2.5 to 50 nmol/cm2; the determination coefficient of the index with anthocyanin content was higher than 0.93.