Abstract:
Nowadays, phytochemicals and antioxidants in plants are raising interest in
consumers for their roles in the maintenance of health. Flavonoids are known for their
health-promoting properties due to the protective effect against cardiovascular disease,
cancer and other non-communicated chronic diseases. Thai diets often use plant-based
foods and various herbs and vegetables in cooking. However, there is little information
on flavonoid content and free radical scavenging activity of herbs and vegetables in
Thailand. Therefore, this study aimed to determine flavonoid content and free radical
scavenging activity of raw and cooked herbs commonly used in Thai dishes. The total
polyphenol content of raw herbs was also investigated.
Nineteen herbs (Holy basil, Sweet basil, Hairy basil, Kaffir lime, Kitchen mint,
Saw leaf herb, Indian mulberry, Spring onion, Chinese chives, Chinese celery, Lemon
grass, Ginger, Lesser ginger, Young galangal, Garlic, Shallot, Young pepper, Bird
chili and Chili pepper) were analyzed for flavonoid content (myricetin, luteolin,
quercetin, apigenin and kaempferol) by using High Performance Liquid
Chromatography method. Free radical scavenging activity was analyzed by 2,2-
diphenyl-1-picrylhydrazyl radical scavenging method. The effect of boiling and stirfrying
on flavonoid content and free radical scavenging activity of all herbs were also
investigated. Total polyphenol content was analyzed by spectrophotometry. The
flavonoid contents of all herbs varied from 0.07 to 48.81 mg per 100g wet weight.
Chinese celery showed the highest total flavonoid content. The major flavonoid in
these plant extracts was luteolin, followed by quercetin, apigenin, myricetin and
kaempferol. There were no significant differences between total flavonoid content of
raw and cooked herbs. Free radical scavenging activity of all herbs ranged from 0.1 to
1.4 mmole Trolox Equivalent per 100g wet weight. Lesser ginger showed the highest
free radical scavenging activity. There was no significant difference in free radical
scavenging activity between raw and cooked herbs. Total polyphenol content of raw
herbs ranged from 42.1 to 579.0 mg gallic acid equivalent per 100g wet weight. There
was no correlation between total flavonoid content and free radical scavenging activity
whereas free radical scavenging activity exhibited a significant linear correlation with
total polyphenol content.
These findings suggest that variations in the compositions and quantity of
flavonoid content and free radical scavenging activity in each herb indicate the
importance of eating a variety of plant foods in every meal.