Effect of fertilization and type of pruning on quality of fresh and dehydrated Stevia rebaudiana

Mestrado em Engenharia Alimentar - Instituto Superior de Agronomia - UL

Stevia rebaudiana is tropical and sub-tropical plant and has been received a large body of attention due to its potential as natural sweetener. In order to contribute to the optimization of the agricultural production in a coastal region in the Lisbon area, with mild climate, an on-farm study was conducted under a context of social agriculture. It was investigated the effects of two levels of pruning and two regimes of fertilization on the plant’s biomass yield and quality, including accumulation of steviol glycosides. The quality differential of leaves was quantified after a customized solar drying coupled with a pre-heat abiotic stress procedure. The results showed that, when growing under just basal fertilization, plants were higher, independently of pruning severity. Additional (foliar) fertilization in light-pruned plants lead to more leaves that in severe-pruned ones and higher leaf areas were observed under severe pruning. Glycosides concentration was not influenced by fertilization, but it was positively influenced by severe pruning resulted in increased amounts, in ca. 29.38% in case of leaves without additional fertilization. In the same time, severe-pruning resulted in higher increase of Stevioside, responsible for bitterer aftertaste, when compared to Rebaudioside A (Rebaudioside A: Stevioside ratio = 0.89). The leaves of Stevia were subjected for 2h to pre-heating and 18h24m of active drying using a SOLAR DRYER until 10.00% of humidity, and with total soluble solids increased ca. 18% and pH decreased ca. 4%. The drying procedure increased Glycosides to 43.06 mg/g dry leaves, from 36.82 mg/g, suggesting secondary metabolites accumulation as a response to abiotic stress. The level of phenolic compounds increased in 100% and antioxidant activity was ca. 3.01 (ABTS) and 4.40 (DPPH) fold higher.