Antioxidant activity of various fractions of subcritical water extracts obtained from tea and tea-like plants

BSc. Asad Walayat, BS

Master's thesis

Abstract:

Oxidative stress is caused by an imbalance in accumulation and production of reactive oxygen species (ROS) in living cells and the biological systems ability to destroy the reactive products. Tea (Camellia sinensis) belongs to family Theaceae and is the most widely used beverage globally following only fresh water. This contains considerable amount of antioxidants, particularly the phenols that are commonly known to have the ability to lower the risk of the development of some serious diseases. Yerba mate (Ilex paraguariensis) is traditionally used tea-like beverage, and its leaves contain antioxidants while the extracts and isolated compounds from yerba mate showed pharmacological properties. The bioactive compounds are extracted from tea and tea-like plants to produce value added products by various extraction method in which different solvents are used. Previously, different antioxidant compounds from plant extracts were obtained by environmentally non-friendly, time taking, and inefficient methods. The green extraction techniques use less hazardous chemical, safer solvents, reduce time analysis, and prevent pollution. Subcritical water extraction (SWE) is a greener and faster method for the extraction of antioxidant compounds by using only water (solvent). In our study, antioxidant activity and total phenolic content (TPC) of different SWE fractions (1st 2min, 2nd 2min, 3rd 2min, 4th 2min, and 5th 2min; 1st 5min and 2nd 5min, and 10min) and water infusion (WI 10min) of green tea, black tea, and mate extracts were evaluated and compared. Their antioxidant activity was evaluated by DPPH and ORAC method while TPC was determined by Folin-Ciocalteu assay. Overall, in our results ORAC assay showed strongest antioxidant activity in I. paraguariensis – mate, SWE 3rd 2min fraction with the lowest IC50 of 5.55 µg/mL among all cases. In C. sinensis – green tea, SWE 2nd 5min fraction showed strongest antioxidant activity with the IC50 9.73 µg/mL determined by DPPH method and highest TPC 778.53 mg GAE/g among tested species. This study proved that SWE is an effective method for the extraction of important bioactive compounds, but its extraction efficiency is affected by extraction time. Moreover, effectiveness depends on plant species, as the most active fractions differ between C. sinensis (SWE 2nd 5min fraction) and I. paraguariensis (SWE 3rd 2min fraction). Thus, the extraction parameters should be optimized according to evaluated species.

Keywords

Aquifoliaceae, antioxidants, fractionation, non-conventional extraction method, tea plant

Language used: English

Date on which the thesis was submitted / produced: 28. 4. 2024

Thesis defence

• Date of defence: 4. 6. 2024
• Supervisor: Ing. Johana Rondevaldová, Ph.D.
• Reader: Jan Tauchen, Ph.D.

Czech University of Life Sciences Prague

Faculty of Tropical AgriSciences

Master programme:
Tropical Crop Management and Ecology