(1) DPPH assay

DPPH assay was used to evaluate the free radical scavenging activity of each sample as described by Neo with slight modifications [18]. Briefly, a certain amount of different extracts was dissolved in 70% ethanol aqueous solutions. One milliliter of the sample solution was then mixed with 3 mL of 0.1 mM DPPH that dissolved in ethanol in the dark for 30 min. The DPPH radical-scavenging rate was expressed as follows:

DPPH radical-scavenging rate % = (A517, control − A517,sample)/A517,control × 100%

A517,sample and A517,control are the absorbance of DPPH solution with or without samples.

## (2) Lipid peroxidation (LPO) assay

First, the yolk lipoprotein solution was prepared as follows: albumen was removed from fresh eggs and the yolk was mixed with the same volume of 0.1 mol/L phosphate buffer (pH 7.4). After shaking for 10 min, the mixture was diluted into 1:25 using phosphate buffer. The obtained solutions were kept at 4 ◦C. Then, 0.2 mL of the above solutions was serially mixed with 0.1 mL of tested sample, 0.2 mL of FeSO4 and 1.7 mL phosphate buffer. The mixtures were incubated at 37 ◦C for 1 h followed by adding 0.5 mL of trichloroacetic acid (TBA, 20%, *w*/*v*) solution. After 10 min incubation, the mixture was centrifuged at 4000 rpm for 10 min. The supernatant (2 mL) was taken out and mixed with 1 mL of TBA (0.8%) in a boiling water bath for 15 min. After cooling down to 25 ◦C, the absorbance was monitored at 532 nm. The LPO suppression ratio was determined as follows: LPO suppression ratio (%) = ((Acontrol − Asample)/Acontrol) × 100%

Asample and Acontrol are the absorbance of solution with or without samples.

#### *2.5. Encapsulation of Nervilia fordii Extract by Electrospinning*

NFE was first prepared according to the optimized extract conditions described in Section 2.2. After that, the blending solution of PVA with PVP containing NFE was achieved as follows. First, 10%~15% (*w*/*v*) of PVA solution was prepared by stirring at 80 ◦C for 2 h. Then, the NFE-loaded PVP solution that was dissolved in 90% ethanol was added into the above PVA solution with a volume ratio of 1:1 to achieve a total polymer mass ratio and NFE of 12.5% and 4%, respectively. Finally, the electrospinning solution was injected into a syringe (21# needle), and the electrospinning process was conducted as a feed rate of 0.3 mL/h, voltage of 16 kV and distance of 14 cm. The encapsulation efficiency (EE) and loading capacity (LC) of NFE were determined based on the measurement of the amount of non-encapsulated extract. In brief, hexane was used to remove the free NFE from the electrospun nanofiber for 2 min, and the absorbance of obtained solution was measured at 472 nm. A series of NFE solution dissolved in hexane was used to establish a calibration curve. The EE and LC were determined as below:

EE% = (theoretical mass of NFE − free mass of NFE)/theoretical mass of NFE ∗100

#### LC% = (theoretical mass of NFE − free mass of NFE)/the mass of fiber∗100

#### *2.6. Characterization of the Electrospun Fiber Mat*

*Scanning Electron Microscopy (SEM)*. The morphology of the obtained fiber was observed by a 3700 N scanning electron microscopy (SEM, Hitachi, Japan). The average diameter of fibers and the fibers size distribution was analyzed by Image-J software.

*Fourier transform infrared Spectroscopy (FTIR)*. The interactions among PVA, PVP and NFE were investigated by FTIR spectroscopy (Bruker-VERTEX 70, Germany). The analysis was conducted under wave number of 3800–500 cm<sup>−</sup><sup>1</sup> and resolution of 4 cm<sup>−</sup>1.

*X-ray diffraction pattern (XRD)*. The XRD pattern of the different composite fibers was recorded to examine the crystallography of the prepared films using a MiniFlex 600 diffractometer (RigaKu, Tokyo, Japan) with Cu-Kα radiation. Data were collected in the 2θ range from 5◦ to 60◦ with a step of 0.02◦.

*Thermogravimetric Analysis (TGA).* The thermal property of the fiber mats was characterized using a TGA Q500 (TA Instruments, New Castle, DE, USA). The sample was heated from 25 ◦C to 700 ◦C with a heating rate of 20 ◦C/min under nitrogen gas atmosphere.

#### *2.7. Oxidative Stability in Accelerated Storage Test*

The oxidative stability of encapsulated fish oil was analyzed under storage conditions of 45 ◦C since low and ambient temperatures require a relative long period of time. As described previously [19], 10 mL of fish oil sample was aliquoted into 20 mL brown glass vials, and 20 mg TA fibrous mat (2 cm × 3 cm) were added, followed by incubation at 45 ◦C in the dark for 30 days, as shown in Figure 1. This subject is of primary importance, since the goal of the paper is to evaluate the potential application of the antioxidant film as a pouch or direct contacting material. The un-encapsulated fish oil was used as the control, while oil samples with pure PVA/PVP film were used as a negative control. Peroxide value (PV) analysis was conducted by taking different amounts of samples out at different intervals as follows [20]. Briefly, 3 g of fish oil sample was dissolved in 50 mL of acetic acid and chloroform mixture (3:2 *v*/*v*). Then, 1 mL of saturated KI solution was added and the mixture was kept in the dark for 1 min. After adding distilled water (50 mL), the mixture was immediately titrated with 0.01 mol/L of sodium thiosulfate until the yellow color had almost disappeared. The PV value was determined as follows:

> PV value (mEq of O2/kg sample) = 12.69 × 78.8 × (VS − VB) × C/m.

where VS and VB is the volume of titrant used in the titration of oil sample and a blank without any oil sample (mL), respectively, C is the concentration of sodium thiosulfate (mol/L) and m is the weight of oil sample (g).

**Figure 1.** The schematic diagram for measuring the fiber mat's antioxidant activity on fish oil oxidation.
