2.5.4. Gas Permeability

The theory of measuring the gas permeability of the film uses the traditional differential pressure method. The films were cut into a 10 cm × 10 cm size and were measured with a BSV-1A gas permeability tester (Lab Stone, Guangzhou, China). The single gas permeability of the film was determined by changing the gas source (O2, CO2, or N2) in the room temperature. The gas permeability coefficient of the film (P) is calculated as follows:

$$P = \frac{\Delta \mathbf{p}}{\Delta \mathbf{t}} \times \frac{\mathbf{V}}{\mathbf{S}} \times \frac{\mathbf{T}\_0}{\mathbf{P}\_0 \times \mathbf{T}} \times \frac{\mathbf{D}}{(\mathbf{p}\_1 - \mathbf{p}\_2)} \tag{2}$$

The ideal gas selectivity of the film can be obtained by calculating the quotient of the permeability of the film under different gas sources.

Where Δp/Δt is the arithmetic mean of changes in hourly gas pressure in the infiltration chamber; V is the volume of the infiltration chamber; S is the area of the film; T is the test temperature; p1−p2 is the pressure difference between the two sides of the film; T0 and p0 are the temperature and pressure under standard conditions, which are 273.15 K and 101,315 Pa, respectively, and D is the thickness of the film.

### *2.6. Pretreatment and Storage of Cherry Tomatoes*

Fresh cherry tomatoes without mechanical damage were manually screened and precooled at 4 ± 1 ◦C and 90% relative humidity for 24 h. The samples (250 ± 10 g) were randomly packed ina1L packaging box (PP), respectively. The surface of the box was sealed with AGO/SPEEK films using a JSMAP-1D100F-S semi-automatic modified atmosphere packaging machine (JuGang Machinery Manufacturing Co., Ltd., Shanghai, China). The temperature, pressure, and heat-sealing time of the packaging machine were 110 ± 5 ◦C, 1.8 kPa, and 1 s, respectively. Samples without packaging were set as control group. The packaged samples were stored in a thermo-hygrostat at 8 ± 1 ◦C for 30 days. The physiological and biochemical properties of cherry tomatoes were evaluated every 5 days.

### 2.6.1. Internal Atmosphere Composition

Concentrations of CO2 and O2 in the box were monitored using an OXYBABY M+ gas analyzer (Zillion Corporation, Shanghai, China). During the measurement, a customized sealing gasket with a size of 1 cm × 1 cm was pasted on the package, and then the needle of the gas analyzer was inserted into the package. The sensor of the gas analyzer that connected to the needle automatically collects gas samples for measurement in 10 s and the actual values of O2 and CO2 volume ratio (%) would be displayed on the screen of the gas analyzer in real time.
