Optimization of Ultrasonic-Assisted Extraction of Antioxidant Compounds from Starfruit (Averroha carambola L)Leaves

Abstract

Extracts of starfruit leaves (SL) were used with a response surface methodology (RSM) to optimize experimental conditions for ultrasonic-assisted extraction (UAE). A 33-1 fractional factorial design (extraction-time XET, pulse-cycle XPC and sonication-amplitude XSA) was employed for UAE, and SL extracts were characterized by total soluble polyphenols (TSP) content and antioxidant capacity (1,1-diphenyl-2-picryl-hydrazyl [DPPH], 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) [ABTS] and ferric-ion reducing antioxidant power [FRAP]). SL extracts showed TSP values between 329.71 and 383.30 mg GAE/g. The best conditions to obtain the highest values for DPPH, ABTS and FRAP activity were 690.18 (XET = 15 min, XPC = 0.7 s, XSA = 100%), 250.59 (XET = 45 min, XPC = 1 s, XSA = 40%) and 355.12 (XET = 30 min, XPC = 0.4 s, XSA = 70%) mmol TE/g, respectively. The experimental data was also adjusted in a polynomial quadratic model. The optimal conditions for different variables were determined as XET = 22.2 and 45 min, XPC = 0.4, 0.8 and 1 s and XSA between 55 and 100%. The predicted conditions can be useful in further analysis to obtain and improve a good extraction of antioxidants and TSP in SL using UAE. Practical Applications Averroha carambola L (starfruit) is consumed in some tropical countries and is considered as an exotic fruit; however, the leaves of their tree are traditionally used as an infusion because of their healthy effects. The combination of an emerging technology, as ultrasound-assisted extraction, a practical experimental design and the use of statistics, as response surface methodology, can be used to optimize the extraction of antioxidants compounds in the leaves of A. carambola. This simple and practical proposal can be useful for those researchers and/or industry sectors that are searching to implement new and nonconventional techniques in the extraction of bioactive compounds, as well as a more comprehensive use of starfruit leaves extracts for a potential development of products or food ingredients.