The number of people suffering
cardiovascular diseases, diabetes, hypercholesterolemia and obesity has
increased globally. For this reason, the demand for non-caloric sweeteners has
increased while sugar consumption has decreased. In this context Stevia plays
an important role. Besides being a natural sweetener, stevia leaf extracts have
other interesting properties, including decreasing blood pressure,
improving digestion and gastrointestinal function and protecting against dental
caries.
The sweetener
compounds in Stevia, steviol glycosides (SG), are mainly found in the leaves.
The SG content depends on the plant’s growth stage and is usually highest just
before flowering. In temperate areas, Stevia is a polyannual crop (5 - 7
years) with a vegetative period lasting from April-May until October, during
which time the crop can be harvested two or three times. This research
focused on the need for knowledge about Stevia’s response to temperate climates
in Southern Europe.
Two field assays
were established from June to October 2013 at two sites in Navarra (Spain). The
biomass and content of the two major SG, stevioside (ST) and rebaudioside A
(RA) were measured using High Performance Liquid Chromatography (HPLC) in 66
cloned plants at different developmental stages. Scatterplots
of dry leaf biomass, leaf-to-stem ratio, ST and RA versus time after planting
were performed and a polynomial surface for each site was fitted using local
polynomial regression fitting with the loess function from the statistical
software R.
The results indicated that leaf biomass increased with time at both
sites, but peaked at different dates. The dynamic of ST percentage in leaves
throughout plant development differed between the two sites. The dynamic of RA
percentage in leaves throughout plant development also differed between the
sites.
In conclusion, though
the results from the two sites showed different SG leaf content dynamics during
the plant growth, the optimum harvest date at both sites coincided with the
bud-flowering stage at the beginning of September (around 96 days after
planting), when a ST yield of 27 g·m-2 was reached. And the
results show that stevia can be successfully cultivated in this region, good
glycoside yields are obtained under the long daylight
conditions, and there is a long vegetative growth period (from spring to late
summer).
Article by Ana
Belen Guerrero, et al, from Universidad Pública de Navarra, Campus de
Arrosadia, Pamplona, Spain.
Full access: http://mrw.so/4Edr87
Photo credit: M. Martin
Vicente on Visualhunt/CC BY.
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