Volatiles compounds composition: Stevia field plants in mediterranean conditions, greenhouse plants and plants in vitro
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A major concern about public health is the control of obesity. The search for new natural sweeteners, as an alternative to synthetic compounds like cyclamates or aspartame, brought Stevia rebaudiana (Compositae), a sweet plant native to South America, to the attention of the scientific community. S. rebaudiana has been produced mainly for its stevioside compounds but it contains other metabolites with potential therapeutic benefits such as alkaloids, hydroxycinnamic acids, oligosaccharides or essential oils. The characterization of the chemical profile of micropropagated plants, as well as greenhouse and field grown plants, is important to ensure the quality of the plants to supply to Stevia growers.
Multiplication rate and fresh weight were determined for plants micropropagated in MS media A with sucrose (20g.L-1) and without growth regulators and MS media B with kinetin (0.5mg.L-1) and sucrose (20g.L-1). Apart from spontaneous rooting rate determination, induction of plant rooting by auxin shock, using IBA (2mg.mL-1), was also evaluated.
Acclimatization in greenhouse was performed with hydro atomization nozzles working every 10 minutes. Plants on the field were fertilized by a nutrient solution with N, P2O5, K2O and B.
In vitro multiplication rate was 300% per month, fresh weigh after a 4 week subculture was 0.9g. Spontaneous rooting rate was less than 4% after 4 months but induced rooting achieved 30% of plants with developed root system after 1 week and 70% after 2 weeks. Acclimatization rate was 100% after 2 weeks.
Acclimatization was performed in greenhouse with 360º hidroatomizing spires working each 10 minutes and the acclimation rate in the greenhouse was of 100% for both medium after 2 weeks.
There were extraction of essential oils with Clevenger apparatus for Yield purposes with average yield values below 0.6 %. In Clevenger, six samples were from Vilariça region and two from micro propagation, one was MS medium without growth regulators and the other was MS medium with 0.5 mg/L kinetin.
In LN the extractions from four different sources, that are represented in figure 6. The essential oil identification was between 75,5 and 83% for the three samples and the results are not very different in the compounds. Volatiles identification revealed identical composition in all samples, with α-pinene (11-31%), bicyclogermacrene (5 19%), trans-β-farnesene (7-15%), β-elemene (6-10%) and β-caryophyllene (3-10%) as major compounds.
Cultivated Stevia shows the higher value in the sequiterpenes hydrocarbons (54,4%), oxygen-contaning monoterpenes (3,2%) and oxygen-contaning sequiterpenes (7,1%). In vitro Stevia Media A and B the value are only very different in monoterpene hydrocarbons and other compounds, but the other value are very similar or exactly the same. In general cultivated and greenhouse. Stevia have higher values for sequiterpenes and the in vitro Stevia have higher values for monoterpenes.
