EFFECTS OF PHOTOSELECTIVE NETS ON PHENOLIC COMPOSITION IN APPLE FRUITS

Apple phenolic compounds synthesis is at least partially regulated by environmental light conditions. Colored nets is an emerging technology that alters the light quantity/quality conditions, but poor information exists about its effect in apple phenolic composition. The aim of this research was to evaluate the effect of different colored nets on flavonoid and chlorogenic acid levels in apples. 'Fuji' apple fruit from sun-exposed parts of the trees were covered with the following (Polysack Industries, Israel) colored nets: red (RS), blue (BS), pearl (PS) shade nets, monofilament red hail net (RH) and control (full sunlight), and arranged in a random block design with three replicates. Spectra irradiance (μmol m-2 nm-1) was measured using a LI-1800 spectroradiometer (LI-COR, Lincoln, NE, USA). Photosynthetic photon flux (PPF, μmol m-2 s-1) was quantified through a LI-190 quantum sensor (LI-COR, Lincoln, NE, USA) and UV radiation by a UV-340A light meter (Lutron Int., Japan). Cyanidin 3- galactoside (anthocyanin), quercetin 3-glucoside and chlorogenic acid were quantified by high performance liquid chromatograph (Waters Corp, Milford Mass, USA). Colored nets did not affect chlorogenic acid content of apple fruit. On the contrary, apple peel under colored nets contained on average 2- to 6-fold less anthocyanins and quercetin 3-glucoside than the control. The various nets however, were not similar: apples grown under RH presented 5-fold more cyanidin 3-galactoside than PS, while BS increased 2-fold the amount of quercetin 3-glucoside compared to PS. RH transmitted 15-20% more PPF and UV light than PS. PPF and UV transmission did not differ among BS and PS, whereas BS enhanced the proportion of blue (400-500 nm) light transmission. Results demonstrate that colored nets did not have a detrimental effect on chlorogenic acid content, but had important effects on the anthocyanin and quercetin synthesis in apples, linked to quantity and quality light changes. Considering netting is a necessary practice to insure sustainable apple fruit production and quality. More knowledge is necessary to obtain anthocyanin and quercetin content enhancement by this technolog