ENHANCEMENT OF FUNCTIONAL COMPOUNDS IN ALLIUM VEGETABLES WITH UV RADIATION

Ultraviolet B induced bioactive changes of enzymatic and non-enzymatic antioxidants and lipids in Trigonella foenum-graecum L. (Fenugreek)

Ultraviolet radiation (UV) altered plant metabolism. Hence Trigonella foenum-graecum L. (Fenugreek) exposed to UV-B radiation for studying the bioactive changes that may be useful in captive farming. UV-B treatment altered plant growth, and extent of alterations depended on the duration of radiation treatment. Photosynthetic pigments such as chlorophyll and carotenoids decreased after radiation exposure. But bioactive components such as anthocyanin, flavonoids, and phenolics increased after UV-B treatment. Phenylalanine lyase enzyme activity and peroxidase activity also increased with 4.0 hr UV-B exposure even though 8.0 hr exposure decreased the activity of these enzymes. Total lipid content of the plants increased after UV-B exposure. Changes in aromatic oil composition observed due to UV-B exposure, and the changes pointed shifting of plant metabolism towards the synthesis of short chain fatty acid contain lipids and non-enzymatic antioxidants.

Medicinal Plant Active Compounds Produced by UV-B Exposure

Ultraviolet (UV) radiation is a part of the sunlight reaching Earth surface. The UV spectrum of solar radiation is by convention divided into three parts: UV-A: 310–400 nm, UV-B: 280–310 nm and UV-C: less than 280 nm. UV-B is the most energetic component reaching Earth surface because the stratospheric ozone layer effectively absorbs completely wavelengths below 290 nm. UV-B is an increasing threat due to increasing UV-B levels on Earth surface as a consequence of depletion of stratospheric O₃. In general, the effects of atmospheric UV-B radiation are negative for biological life. Enhanced levels of UV-B radiation can indeed negatively change plant physiological processes, growth and productivity. However, while studying UV-B effects on medicinal plants, some interesting phenomena have been discovered. For example, basil plants respond positively to UV-B radiation by increasing oil yield (Chang et al. J Horticult For 1:27–31, 2009). In other studies medicinal plants show beneficial aspects in term of increase in volatile oil yield and secondary metabolite production (Kumari et al. Ecotoxicol Environ Safety 72:2013–2019, 2009c, 2010). Medicinal herbs have great market value in India and worldwide. The medicinal value of plants depends upon phenolics, antioxidants and volatile yield. Therefore further UV-B experiments increasing the levels of these compounds are needed.

Here we review the effect of UV-B exposure on metabolites, volatiles, and antioxidants potential in medicinal plants. This chapter reports: (1) aspects of the global market for medicinal and aromatic plants in India in order to assist the medicinal plant industry to make informed decisions. (2) The biodiversity loss due to wild harvesting of plants, and as an alternative the cultivation strategy of medicinal plants. (3) Main medicinal plant species having rich antioxidant potential. (4) Main secondary metabolites of plant origin such as phenylpropanoids, terpenes, alkaloids, and volatile oil, and other important metabolites containing high antioxidant level used in human diet and health. (5) UV-B factors that enhance the quality of medicinal plant by increasing the content of secondary bioactive products. (6) Secondary metabolic pathways involving regulation of key enzymes, chalcone synthase, and phenylalanine ammonia lyase. Understanding of UV-B responses on secondary plant metabolites expand new opportunities for plant enriched in medicinal active compounds.