Abstract
Sweet basil (Ocimum basilicum Linnaeus) is aromatic herb that has been utilized in traditional medicine. To improve the phytochemical constituents and pharmaceutical quality of sweet basil leaves, ultraviolet (UV)-B irradiation at different intensities (2.30, 3.60, and 4.80 W/m2) and durations (4, 6, 8, and 10-h) was applied at the post-harvest stage. Total flavonoid content (TFC) and total phenolic content (TPC) were measured using spectrophotometric method, and individual flavonoids and phenolic acids were identified using ultra-high performance liquid chromatography. As a key enzyme for the metabolism of flavonoids, chalcone synthase (CHS) activity, was measured using a CHS assay. Antioxidant activity and antiproliferative activity of extracts against a breast cancer cell line (MCF-7) were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) assays and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays, respectively. UV-B irradiation at an intensity of 3.60 W/m2 increased TFC approximately 0.85-fold and also increased quercetin (0.41-fold), catechin (0.85-fold), kaempferol (0.65-fold) rutin (0.68-fold) and luteolin (1.00-fold) content. The highest TPC and individual phenolic acid (gallic acid, cinnamic acid and ferulic acid) was observed in the 3.60 W/m2 of UV-B treatment. Cinnamic acid and luteolin were not detected in the control plants, production being induced by UV-B irradiation. Production of these secondary metabolites was also significantly influenced by the duration of UV-B irradiation. Irradiation for 8-h led to higher TFC, TPC and individual flavonoids and phenolic acids than for the other durations (4, 8, and 10-h) except for cinnamic acid, which was detected at higher concentration when irradiated for 6-h. Irradiation for 10-h significantly decreased the secondary metabolite production in sweet basil leaves. CHS activity was induced by UV-B irradiation and highest activity was observed at 3.60 W/m2 of UV-B irradiation. UV-B treated leaves presented the highest DPPH activity and antiproliferative activity with a half-maximal inhibitory concentration (IC50) value of 56.0 and 40.8 µg/mL, respectively, over that of the control plants (78.0 and 58.2 µg/mL, respectively). These observations suggest that post-harvest irradiation with UV-B can be considered a promising technique to improve the healthy–nutritional and pharmaceutical properties of sweet basil leaves.
Highlights
Flavonoids, which are important secondary metabolites in plants, are involved in resisting environmental stress and regulating the growth of plants [1]
The higher irradiation intensity (4.80 W/m2 ) did not demonstrate a higher level of Total flavonoid content (TFC), indicating that when the intensity is too high, the amount of TFC consumed, which captures the reactive oxygen species (ROS) and repairs the oxidative damage caused by the UV-B irradiation, was almost equal to the increase of TFC [8]
Antiproliferative and antioxidant activity of sweet basil mostly correlated with flavonoids followed by phenolic acids
Summary
Flavonoids, which are important secondary metabolites in plants, are involved in resisting environmental stress and regulating the growth of plants [1]. The biosynthesis of flavonoids in plants begins with the shikimate pathway, and intermediate products, such as chalcone and isoflavonoids, are formed via the phenylpropanoid pathway [2,3]. These flavonoids are conjugated to other flavonoids and glycose to form final products including anthocyanin and flavonol glycoside. High levels of UV irradiation, lead to increased concentrations of antioxidants in plants and is considered as a tool for enhancing contents of bioactive compounds in fresh crops, herbs, fruit and vegetables after harvest [12,13]. It has been reported that irradiating parsley (Petroselinum hortense) with
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