Antioxidants Capacity, Phenolic and Oxalate Content from Two Varieties of Solanum melongena at Different Maturity Stages

Abstract

Aims: To investigate the antioxidant activities, total phenolic and oxalate contents in two varieties of eggplant (Solanum melongena) (terung telunjuk (TT) and terung rapuh (TR)) at different maturity stages.
 Study design: Each sample was extracted three times (n=3) for the antioxidant activities, total phenolic and oxalates content. All the data were analysed by using ANOVA and Tukey Pairwise tests.
 Place and duration of study: Malaysian Agricultural Research and Development Institute (MARDI), between December 2019 and October 2020.
 Methodology: Two varieties of eggplant (TT and TR) were cultivated and the samples were tagged and the fruits were harvested according to their maturity stages (stage 1 – stage 4). Samples were freeze dried and extracted to evaluate the antioxidant activities as well as the total phenolic and oxalate contents.
 Results: Total phenolic contents (TPC) in TR were lower from stage 1 to stage 3 but high at over mature stage (stage 4) meanwhile TPC in TT increased upon maturity. The DPPH assay from the fruit extracts of TT in all maturity stages showed a stronger antioxidant activity as compared to TR, in which fruit of TT from stage 3 was double in antioxidant activity as compared to TR. The FRAP assay of both eggplants showed extracts of TT having a higher ferric reduction power in all stages as compared to TR. Meanwhile, both eggplant varieties showed different total, soluble and insoluble oxalate contents in all maturity indices. TT had the highest total oxalate content at stage 1 as compared to TR while the soluble oxalate content increased in TR in all maturity stages. The highest percentage of soluble oxalate content was observed in TR at stage 4 with 95.5%. Conclusion: Phytochemical findings from these eggplant varieties showed their potentials to improve livelihood and public health. More comprehensive studies on the bioactive compounds, structural elucidation and pharmacological evaluation are to be conducted to understand the possible effects of these phytochemical results.

Comparative Phytochemical Analysis of Bambara Groundnut (Vigna subterranea) and others Vigna spp. with Respect to its Nutritional, Antinutritional and Antioxidant Properties

“…Total phenolic content of the crude extract was determined by the Folin-Ciocalteu method with some modifications [10]. Briefly, 50 µL of the crude extract were mixed with 100 µL of Folin Ciocalteau's phenol reagent (Merck, Germany).…”

“…The extraction for the total oxalate (TOX), soluble oxalate (SOX) and insoluble oxalate (IOX) contents using HPLC were determined based from previous literature review with minor modifications [10,[12][13]…”

“…A 5 µl filtered sample from acid and water extracts were injected through HPLC system with Diode-Array Detection at 210 nm (Agilent chromatography System 1200 Infinity Series). The oxalate determination using HPLC was based from the previous literature with minor modification [10]. The separation was done using Rezex ROA ion exclusion organic acid column, 300 × 7.8 mm (Phenomenex, Torrance, CA, USA) attached to a cation H+ guard column.…”