Nutritional Value, Bioactive Compounds, and Antioxidant Activity of Phak-liang (Gnetum gnemon Linn. var. tenerum Markgr.) in Surat Thani Province, Thailand

Abstract

The nutritional value, bioactive compounds, and antioxidant activity of Phak-liang (Gnetum gnemon Linn. var. tenerum Markgr.) were investigated. The indigenous vegetables were collected from three districts; Muang, Bannasarn, and Khirirat Nikom in Surat Thani Province. The nutritional value of the samples was carried out according to the methods of AOAC. The moisture contents ranged from 84.72-87.52%, and the ash contents ranged from 0.78-1.07% fresh weight. The percentage of fiber, protein, fat, and carbohydrate in the leafy vegetables were in the range of 3.06-3.81, 3.44-4.68, 0.65-1.08 and 7.49-9.55 fresh weight, respectively. The samples were analyzed by ICP-OES for their mineral determinations. The amounts found in the samples, in descending order were: K > Ca > Mg > Mn > Na> Fe > Zn > Cu. Considering the amounts of minerals found in the vegetable and their recommended daily values by the Bureau of Nutrition (Ministry of Public Health, Thailand), the daily value (DV) percentage of Mn in the samples were relatively high (28.45-96.65%), whereas K, Mg, Ca, Fe, Cu and Zn contributed from 1.29–8.42% of the daily values. The vegetable had negligible amounts of Na (0.03 - 0.07% of the DV). The antioxidant capacities were analyzed using Ferric Reducing Antioxidant Power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The results showed that antioxidant activity increased by the concentration of the ethanol extracts. The FRAP values of the extracts ranged from 89.01-160.70 µM FeSO4/100 g dry weight, and the IC50 values calculated for DPPH radical scavenging activities of the extracts ranged from 54.37-60.57 mg/mL. The results suggested that Phak-liang is a potential source of natural phytochemicals and could be used for health promotion in the community.