Bc1340

Under alkaline conditions, phenols can reduce tungstomolybdic acid to produce blue compounds with a characteristic absorption peak at 760 nm (6 (link)). According to the instruction of the extraction kit (BC1340, Solarbio, Beijing, China), standard samples of gallic acid (98% in purity, BC1340, Solarbio, Beijing, China) at concentrations of 0.15625, 0.078125, 0.039, 0.02, 0.01, 0.005, and 0.0025 mg/ml were prepared to construct a standard curve with R² value equal to 0.9996 (y = 0.0183x-0.0024). Then, the content of TP extracted from fruit pulp was calculated based on the standard curve.

Ascorbic acid (AsA) content was quantified via an assay kit (Solarbio, BC1230) at 265 nm based on the reaction between ascorbate oxidase and AsA to form dehydroascorbic acid, meanwhile assay kit (Solarbio, BC1170) was used for the reduced glutathione (GSH) content. GSH undergoes a reaction with 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) to form 2-nitro-5-mercaptobenzoic acid and glutathione disulfide and the absorbance was read at 412 nm. The plant flavonoids were determined with a colorimetric assay kit (Solarbio, BC1330) at 470 nm, and the plant total of phenol was measured by the Folin-Ciocalteu method according to the manufacturer’s instructions at 760 nm (Solarbio, BC1340). ASA and GSH were extracted in 0.1 g of fresh leaf samples with 1 mL of extraction solution given by the assay kits. The total phenol was extracted with 2.5 mL of 60% alcohol and the flavonoids with 1 mL of 60% ethanol.

The contents of the free and bounded phenolics were determined with a plant total phenol content assay kit (BC1340, Solarbio, Beijing, China) based on the Folin–Ciocalteu method. The content value is on behalf of gallic acid (mg GAE/100 g). The total phenolic content was calculated as the sum of the free and bounded phenolic.