Cyclotriphosphazenes: Pre-harvest foliar applications improve antioxidant activity by increasing phenolic compounds in Lavandula angustifolia Mill.

Abstract

The versatile chemical structures of cyclotriphosphazenes (CTPs) and their derivatives make them useful for various applications, including serving as plant nutrients to enhance the production of bioactive compounds. Therefore, the effects of 30 and 60 mg/L concentrations of CTPs (Compound 4 and 5) sprayed foliar at two different stages (pre-flowering stage and full-flowering stage) on total flavonoids and phenolic content, antioxidant activity, and accumulation of phenolics in lavender (Lavandula angustifolia Mill.) were investigated. Compounds 4 and 5 were purified by using column chromatography. The structures of the compounds were verified using mass, 1H, 31P nuclear magnetic resonance (NMR) spectroscopy, and Fourier-transform infrared (FT-IR) spectroscopy methods. The highest total phenolic content and antioxidant activity were achieved with Compound 5 (60 mg/L) treatment by using Folin-Ciocalteu and 2,2-diphenyl-1-picrylhydrazyl (DPPH) tests. The phenolic profile was determined by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Compound 4 treatment yielded a higher level of increase in total flavonoids, protocatechuic aldehyde, protocatechuic, caffeic acid, 4-OH benzoic, and salicylic acid, whereas Compound 5 treatment yielded a higher level of increase in vanillic, p-coumaric, ferulic, and rosmarinic acids. CTPs applied during the full-flowering stage resulted in significant increases, such as an 8.7-fold rise in protocatechuic acid, a 4.3-fold increase in protocatechuic aldehyde, and an 8.4-fold surge in caffeic acid. The caffeic acid was strongly and positively correlated with the 4-OH benzoic acid (,834**), vanillic acid (,955**), p-coumaric acid (,670**), and rosmarinic acid (,669**). The results showed that using a suitable cyclotriphosphazene compound(s) and selecting a suitable pre-harvest application time can significantly enhance and optimize the levels of phenolics.