Antioxidant properties and phenolic constituents of selected herbal teas from Sabah

Chia, Kah Fei (2012) Antioxidant properties and phenolic constituents of selected herbal teas from Sabah. Masters thesis, Universiti Malaysia Sabah.

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Abstract

Herbal teas, which are important source of bioactive compounds, are among the functional beverages that getting attention due to its health promoting properties. While the phenolic composition and their biological properties of the more common western herbal teas (e.g. chamomile) have been extensively investigated, herbal teas from Malaysian tropical herbs are relatively unexplored. The aim of this study was to determine the effects of different method of tea preparation (infusion, decoction, and cold infusion) and extraction condition (temperature and time) on antioxidant capacities and total phenolic content of selected herbs (Rhodomyrtus tomentosa, Phyla nodiflora, Ficus deltoidea, and Limnophila aromatic) from Sabah. The interaction effects of the herbs in combination with two commonly consume tea (green tea and black tea) in term antioxidant capacities and total phenolic content was investigated by comparing their experimental antioxidant capacity value of sample mixture with theoretical sum of individual sample antioxidant capacity. Four comprehensive in-vitro antioxidant assay (total phenolic content (TPC), ferric reducing antioxidant power (FRAP), ABTS• radical scavenging capacity (ABTS), and oxygen radical absorbance capacity (ORAC)) were used in this study. For phenolic constituents characterization, a reliable high-performance liquid chromatographic (HPLC) method coupled with diode array detector (DAD) was developed for simultaneous determination of 44 phenolic acids and flavonoids in herbal teas. All herbal teas decoction exhibited promising antioxidant activities ranged from 0.12 to 1.24 mg GAE/mL, 1.06 to 15.66 μmol TE/mL, 1.56 to 16.56 μmol TE/mL, 4.81 to 24.15 μmol TE/mL for TPC, FRAP, ABTS, and ORAC, respectively. Decoction of R. tomentosa exhibits the highest TPC (1.24 ± 0.08 mg GAE/L), FRAP (15.66±0.34 μmol TE/L), and ABTS (16.55±0.49 μmol TE/L). Total phenolics content and antioxidant activities of herbal teas are significantly (p<0.05) higher with the increase of water’s temperature in tea preparation. Higher extraction water temperatures (80, 90°C and 100°C) yielded herbal tea rich in total phenolic content and antioxidant activities for all tested sample indicated that the antioxidant components are heat stable. There was no significant effect (p>0.05) of the extraction time on total phenolic content and antioxidant capacities when the herbal teas extracted at high temperature (80, 90 °C or 100°C). However, extraction time became a factor to influence the phenolics content and antioxidant activities at lower temperature extraction (60 °C or 70°C). Results for interaction study indicated the mixture of different combination of the herbal teas and teas produced additive, synergistic or antagonistic effects, with the antagonism predominated in all assays. Six compounds, namely catechin, epigallocathechin, epicatechin, orientin, vitexin, and isovitexin were successfully identified and quantified in the decoction of F. deltoidea. In conclusion, teas from R. tomentosa and F. deltoidea can emerge as excellent functional beverages as a source of antioxidant in daily diet.

Item Type:	Thesis (Masters)
Keyword:	Herbal teas, Bioactive compounds, Antioxidant capacities, Total phenolic content, Tea preparation methods, Extraction conditions, Rhodomyrtus tomentosa, Phyla nodiflora
Subjects:	T Technology > TX Home economics > TX1-1110 Home economics > TX341-641 Nutrition. Foods and food supply
Department:	SCHOOL > School of Food Science and Nutrition
Depositing User:	DG MASNIAH AHMAD -
Date Deposited:	11 Mar 2025 09:59
Last Modified:	11 Mar 2025 09:59
URI:	https://eprints.ums.edu.my/id/eprint/43089

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