Studies on Phenolic Contents and Biofunctional Activities of Selected Ethiopian Spices and Herbs

Dessalegn, Engeda (2015) Studies on Phenolic Contents and Biofunctional Activities of Selected Ethiopian Spices and Herbs. PhD thesis, Addis Ababa University.

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Abstract

Spices and herbs have been added to foods since ancient times, not only as flavoring agents, but also as folk medicine and food preservatives. They show potential health benefits as they possess antioxidant and biologically active phytochemicals. In Ethiopia, people use dietary spices and herbs to flavor different cultural foods and also as folk medicine. Thymus schimperi (TS), Lippia adoensis var koseret (LAK), Lippia adoensis var. adoensis (LAA), Aframomum corrorima (AC), and Coriandrum sativum leaf (CSL), Coriandrum sativum fruit (CSF), and Coriandrum sativum seed (CSS) have been used as an important food flavoring agents in Ethiopia, and are also claimed to have various health benefits. TS, LAK, and LAA are endemic herbs to Ethiopia. In this study, the phenolic contents, the in vitro antioxidant activities and the effects of heat treatments on total phenolic content (TPC) and antioxidant potentials from the leaves extract of TS, LAK, LAA, CSL, fruit extract of CSF and seed extracts of CSS and AC were reported.The in vitro antidiabetic activity of TS and T. vulgaris (TV) and antiproliferative activity of AC on liver cancer HepG2 cell lines were evaluated. LAK, LAA, AC, CSL, CSF, and CSS were collected from Sidama Zone South Ethiopia. The TS was collected from North Shoa, Ethiopia. The leaf of TV was collected from campus of Dalhousie Agricultural College, Canada. Each dried sample was extracted with five solvents (petroleum ether, water, acetone, methanol, and aqueous: methanol, 20: 80, v/v). The antioxidant activity was determined using 2, 2-dipheny-l-2- picryl-hydrazyl (DPPH) assay method, ferric ion reducing, phosphmolybdenum, ferric ion chelating, and lipid peroxidation assays. The effects of thermal treatments (heated at 100 oC, 150 oC, and 180 oC for 1 and 2 h) on TPC and antioxidant capacity were investigated. The in vitro antiproliferation activity of petroleum ether and aqueous: methanol (20:80, v/v) extracts of AC on liver cancer HepG2 cell lines was conducted using [3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt; MTS] assay. Based on α– amylase and α–glucosidase inhibitions, the in vitro anti-diabetic activity of hot water and aqueous: methanol (20:80, v/v) extracts of TS and TV was evaluated. The TPC ranged from 6.39 ± 0.62 mg GAE/g dried extract up to 122.04 ± 11.59 mg GAE/g of dried extract, while the TFC varied between 0.02 ± 0.01 and 45.11 ± 5.09 mg QE/g of dried extract. Five flavan-3-ols, seven phenolic acids, six flavonols, two dihydrochalcones, and two aliphatic organic acids were identified and quantified. Highest concentrations of total flavonols and phenolic acids were found in TS. Highest flavan-3-ols were found in CSS and highest aliphatic carboxylic acid levels were found in CSL. Q3-Rut was the most abundant flavonol and hydroxycinnamic acid was the most abundant phenolic acid in TS. Catechin (Cat) was the most abundant flavan-3-ols in CSS. The antioxidant activity was concentration dependent. The aqueous: methanol (20:80, v/v) extract of LAA showed highest DPPH radical scavenging (IC50 = 7.96 ± 2.11 g/mL), reducing power (IC50 = 79.55 ± 6.32 mg AAE/g of dried extract), and total antioxidant activity (1.98 ± 0.14 mg BHTE/g dried extract). Water extract of CSS showed the strongest iron chelating activity (IC50 = 53.95 ± 1.22 g/mL), the leaf methanol extract of CSL had the highest percentage of linoleic peroxidation (78.30 ± 2.50%) and CSS showed the highest (82.64 ± 2.47%) inhibition of secondary lipid decomposition products. There were positive relationships (R2 = 0.55–0.95) between TPC and DPPH scavenging activity (%) of the tested plant extracts but negatively correlated with ferrous chelating activity (%). The TPC and DPPH scavenging activity (%) of most of these dietary spices and herbs were increased with the increasing heating temperature and prolong heating time. But LAK and LAA showed reduction in TPC and antioxidant activities when heated at high temperatures and others showed different variation in all the activities. The DPPH scavenging activity (%) was strongly correlated (R2 = 0.86, R2 = 0.80) with TPC whereas the total antioxidant activity was moderately correlated (R2 = 0.59, R2 = 0.45) for all spices and herbs heated at different heating temperatures for 1 and 2 h, respectively. Both aqueous: methanol (20:80, v/v) and boiling water extracts from TS and TV exhibited inhibitory activities against α–amylase and α-glucosidase. Aqueous: methanol (20:80, v/v) extract of TS showed the strongest α-amylase inhibition activity (IC50 = 0.33 ± 0.05 mg/mL), whereas, the hot water extract exhibited the strongest α-glucosidase inhibition (IC50 = 0.05 ± 0.01 mg/mL) activities. The petroleum ether extract of AC showed stronger inhibition of proliferation of HepG2 cells (IC50 = 105.36 ± 6.92 g/mL) than that of aqueous: methanol (20:80, v/v) extract (IC50 = 282.01 ± 43.40 g/mL) treated for 24 h. The findings suggested that the methanol, acetone, and aqueous: methanol (20:80, v/v) herbal extracts (CSL, LAK, LAA, and TS) exhibited stronger antioxidant activities than that of spice (CSS, CSF, and AC) extracts. Except for LAK and LAA, thermal treatment increased the TPC and DPPH scavenging activities of the plant extracts. There is high potential for the polar solvent extracts to be utilized as sources of natural antioxidants in preventing various oxidative stresses, in the control of blood glucose for diabetes and as food preservatives in the functional food industry. However, on the contrary the nonpolar solvent extracts from the seeds of AC showed stronger inhibition of proliferation of HepG2 cell lines than polar solvent extracts suggesting that the nonpolar compounds are also important for their anticancer activity.

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Afamomum corrorima; antioxidant; α–amylase; Coriandrum; α–glucosidase; HepG2; LC-MS; Lipia adoensis; phytochemical; Spices and herbs; thermal treatment; Thymus,
Subjects:	G Geography. Anthropology. Recreation > GN Anthropology Q Science > QD Chemistry Q Science > QH Natural history > QH301 Biology S Agriculture > S Agriculture (General)
Divisions:	Africana
Depositing User:	Selom Ghislain
Date Deposited:	28 Jun 2018 13:42
Last Modified:	28 Jun 2018 13:42
URI:	http://thesisbank.jhia.ac.ke/id/eprint/6168

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