Stevia (Stevia rebaudiana Bertoni) has gained great interests due to its
non-caloric and health related properties with its steviol glycosides and
phytochemical constituents. Currently, it is being utilized as a natural
sweetener in many food formulations such as soft drinks, jams, dairy
products, chocolates, etc. Green extraction techniques using non-hazardous
solvents and yield-enhancing strategies have been subject matters of various
disciplines such as food technology, chemistry and pharmacology. Stevia
powders are industrially produced by aqueous-extraction with further
purification and drying steps. There has been no any report handling
combined microwave and enzyme assisted technique on the extraction of
steviol glycosides and antioxidant compounds to date. The objective of this
study was to determine optimum processing parameters of microwave assisted
enzymatic extraction of steviol glycosides and phenolic compounds by
investigating the effects of independent variables. The plant was collected
from a stevia garden and its leaves were detached from flower part, dried
and milled into powder form before commencement of the treatments.
Operations were performed using a microwave extraction system equipped with
a digital control system for irradiation time, temperature and microwave
power. Viscozyme L which is a widely used cellulolytic enzyme cocktail was
used in this study. The effects of enzyme concentration (1.2 - 60 FBG unit
g-1), temperature (25-60?C) and time (1 - 20 min) were evaluated using a
five-level rotatable central composite design by response surface
methodology (RSM). The validities of models were assessed by ANOVA outputs
which were determination coefficient (R2), lack of fit and Fisher's test
value (F-value). The maximized yields of stevioside, rebaudioside A and
total phenolic compounds were determined as 62.5, 25.6 and 20.7 mg g-1,
respectively at optimum processing conditions which were estimated as 10.9
FBG unit g-1, 53?C and 16 min.
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