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Spectral properties of sweet pepper fruits

Marian Czarnowski*, Stanisław Cebula**

**The Franciszek Górski Department of Plant Physiology
**Polish Academy of Sciences
**Sławkowska 17, 31-016 Kraków, Poland
**Department of Vegetable Crops
**Faculty of Horticulture, Agricultural University
**29 Listopada 54, 31-425 Kraków, Poland

The changes in spectral properties of the sweet pepper fruits were shown during their growth and maturation. In the range of photosynthetically active radiation (PAR, 400-700 nm) the leaves and pericarp of the pepper fruits (cv. Spartacus F1) showed similar absorptance of radiation (about 90%), weak reflectance (about 6%), and low transmittance (about 4%), while in the near infrared (NIR, 700-1100 nm) the spectral properties of leaves differed significantly from those demonstrated by pericarps. The absorptance of radiation achieved 8 and 47%, reflectance 52 and 33%, and transmittance 40 and 20%, respectively. The PAR absorptance by the young fruits reached about 86% and the NIR about 33%. The transmittance of solar radiation through the pericarp of the small, medium, and large pepper fruits was 23, 18, and 14% respectively within the wavelength range from 300 to 1100 nm (GMR, global measurement radiation) and 2.7, 1.9, and 0.8% in the PAR range. The practical aim of the investigation concerned examination of the high PAR absorptance by the green pericarp as the source of the energy for the photosynthesis process in the pepper fruits.

In comparison with the green fruits, the red ones revealed a significantly increased transmittance of solar radiation in the red range, and a slightly decreased one in the near infrared. Yellow-coloured fruits of the pepper (cv. Kerala F1) and cream-coloured ones (cv. Mira) showed quite different special properties. While in the PAR range these two cultivars showed a similar value of the reflectance (33 and 32%), absorptance (53 and 52%), and transmittance (14 and 16%), they differed considerably with regard to their spectral characteristic. Conversely, in the NIR range in both these cultivars a great differentiation on the total value of reflectance (52 and 34%), absorptance (23 and 47%), and transmittance (25 and 19%) occurred. These meaningful differences in the spectral properties of the fruits of the two pepper cultivars are connected with the amount of carotenoids in their pericarp.

Czarnowski M., Cebula S., 1998. Spectral properties of sweet pepper fruits. Folia Horticulturae 10/1: 39-51.