Antioxidant Capacity and UPLC-PDA ESI-MS Phenolic Profile of Stevia rebaudiana Dry Powder Extracts Obtained by Ultrasound Assisted Extraction

Abstract

Stevia leaves, which are commonly used as a natural sweetener in food products, have increased in importance for antioxidant delivery due to their high content of phenolic compounds. In this study, the influence of the drying process on stevia leaves, with regards to phenolic content and antioxidant activity during drying kinetics 40 °C for 7 h, was studied. The effect of solvent concentration and extraction time using a 32 factorial design on total phenol content (TPC), and on antioxidant activity of extracts obtained from dried stevia leaves, by ultrasound assisted extraction (UAE) as alternative method was evaluated. Steviol glycosides contents were also evaluated by a conventional and UAE method. Phenols identification, quantification and purification were performed by Ultra Performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry (UPLC-ESI-MS), Ultra Performance Liquid Chromatography-Photodiode Array (UPLC-PDA) and advanced automated flash purification, respectively. Drying time affected the moisture content of stevia leaves. A constant weight was reached after six hours of drying, and higher antioxidant activity was observed, while the highest TPC was obtained after seven hours of drying. The highest TPC (91.57 ± 8.8 mg GAE/g dw) and antioxidant activity (603.24 ± 3.5 μmol TE/g dw) in UAE method was obtained when ethanol 50% at 5 min was used. Steviol glycosides extracted by UAE were recorded with a content of 93.18 ± 1.36 mg/g dw and 98.97 ± 1.75 mg/g dw for stevioside and rebaudioside A respectively. Six phenolic compounds including four phenolic acids and two flavonoids were identified and quantified by UPLC-PDA, and confirmed by ESI-MS reporting its fragmentation pattern. Diosmin and chlorogenic acid were the most abundant compounds with values of 2032.36 μg/mL and 434.95 μg/mL respectively. As a novelty we found that the antioxidant activity evaluated in partially purified fractions suggested that biological activity might be attributed to the synergistic effect of the six phenols present in the stevia leaves extract. In addition to its sweeting properties, stevia leaves constitute a potential source of polyphenolic compounds, with antioxidant activity that could be used as a food additive.

Comparative Investigation of Amino Acids Content in the Dry Extracts of Juno bucharica, Gladiolus Hybrid Zefir, Iris Hungarica, Iris Variegata and Crocus Sativus Raw Materials of Ukrainian Flora

“…An analysis [51] of the free amino acids composition of 20 Crocus stigma from different countries (Spain, Italy, Greece, Iran) showed that alanine, proline and aspartic acid were the major amino acids in all tested samples. The differences in the obtained results can be explained by the environmental factors, that affect the plant chemical composition [52][53][54][55].…”

Polyphenols from Stevia rebaudiana (Bertoni) leaves and their functional properties

“…In addition, the drying method for fresh leaves also dramatically affects the PPS extraction (Covarrubias‐Cardenas et al., ; R. Lemus‐Mondaca et al., ; Lemus‐Mondaca, Ah‐Hen, Vega‐Gálvez, Honores, & Moraga, ; Periche et al., ). Among the assayed seven drying processes (sun, freeze, shade, convective, vacuum, infrared, and microwave drying), the freeze and shade drying resulted in the highest TPC, while infrared drying yielded the lowest values (R. Lemus‐Mondaca et al., ).…”

Ultrasound-Assisted Extraction of Two Types of Antioxidant Compounds (TPC and TA) from Black Chokeberry (Aronia melanocarpa L.): Optimization of the Individual and Simultaneous Extraction Methods

“…This complex absorbs at a maximum of 765 nm and a Cary 60 UV-Vis spectrophotometer (Agilent Technologies, Santa Clara, CA, USA) with quartz cuvettes was used. This method has been previously used by numerous researchers for other matrices [22,23]. Due to the extraction kinetics and the stability of the complex formed, the samples were kept in the dark for 30 min, which is the time necessary for the formation of the blue complex.…”