*2.1. Materials*

The dried aerial part of *Nervilia fordii* with water content being around 11% was purchased from the Dashenlin Pharmaceutical Co. Ltd. (Guangzhou, China) with phenological stage being September in 2018; 2, 2-Diphenyl-1-picrylhydrazine (DPPH), ascorbic acid (Vc), rutin, gallic acid were obtained from Sigma-Aldrich Co. (Shanghai, China). PVP of molecular weight 1,300,000 was obtained from Aladdin Biological Technology Co., Ltd. (Shanghai, China); PVA (M w 85,000−124,000) was provided by Tianyi company (Guangzhou, China). All other reagents used were analytical grade.

#### *2.2. Preparation of Different Solvent Extracts*

The different *Nervilia fordii* extracts were prepared as follows: 10 g of air-dried aerial part of *Nervilia fordii* plant was mixed with 100 mL of a certain concentration of ethanol solution. The mixture was stirred at a certain temperature (50~90 ◦C) for 2 h, and the residues were re-extracted twice. Filtrates were pooled, and, after the evaporation of ethanol, the concentrated ethanol extract was then extracted with petroleum ether, ethyl acetate, and n-butanol for 4 h, respectively. The supernatants were combined and the residue was re-extracted by repeating the above procedure twice. The effects of variables like the ethanol concentration, temperature and solid-to-solvent ratio on DPPH activity were investigated. Finally, the obtained extracts were freeze-dried and kept in a desiccator for further analysis.

#### *2.3. Determination of Antioxidant Contents in Nervilia fordii Extracts*

## (1) Total phenol content (TPC)

TPC was measured by Folin–Ciocalteu Reagent assay according to a previous study with some modifications [17]. In brief, 100 μL of different concentrations of solvent extracts were individually dissolved in 70% ethanol. Then, 0.5 mL of Folin–Ciocalteu Reagent and 7.9 mL of water were added, followed by shaking. After incubation in the dark for 5 min, the solution was reacted with 1.5 mL of 10% Na2CO3 solution and incubated in the dark for 2 h. After that, the absorbance at 765 nm against a blank was measured. A series of gallic acid standard solution was used to establish a calibration curve. The results were expressed

as mg gallic acid equivalent (GAE)/g extract. For the NFE-loaded film, the sample was first immersed into 10 mL of 70% ethanol. The obtained extract solution from film was then determined by the above method. The TPC is expressed as mg of GAE/g film.

#### (2) Total flavonoid content (TFC)

TFC was calculated by AlCl3-HAc-NaAc (pH 5.5) assay. Briefly, 200 μL different concentrations of solvent extracts were individually dissolved in 70% ethanol. Then 300 μL of 0.1 mol/L AlCl3 solution and 200 μL of HAc-NaAc buffer solution (pH 5.5) were serially added and mixed with 4.5 mL of 70% ethanol. The absorbance at 405 nm was monitored. A series of rutin standard solution was used to establish a calibration curve. The results are expressed as mg rutin equivalent (RE)/g extract.
