*2.9. Mechanical Properties*

The mechanical properties of the SA composite film are measured by using a microcomputer electronic tensile testing machine (QLW-5E, Xiamen Qunlong Instrument Co., Ltd., Xiamen, China) to obtain its tensile strength and elongation at break. The stretching speed parameter of the equipment was set at 50 mm/min. The determination of each type of film was repeated five times, and each repetition was from a different sampling unit.

#### *2.10. Light Transmittance and Opacity of Film*

The transmittance of SA composite film in ultraviolet (UV) and visible light region was determined by double beam ultraviolet spectrophotometer. The detailed determination method was based on Achachlouei et al. [24]. The film sample was cut into rectangular pieces and installed in a quartz cuvette for spectrum measurement. The wavelength of measurement was selected as 200–800 nm. The opacity of the film can be calculated by Equation (1).

$$\text{Operity} = (\lg(\text{1/T}))/\text{d} \tag{1}$$

where T is the light transmittance of the film at 600 nm, and d is the thickness of the sample. The measurements were repeated three times for each type of film.

#### *2.11. The Sustained-Release of CIN in Film in Food Simulants*

The CIN release from the SA nanocomposite film was assessed following a method adapted from Muller et al. [25]. Sodium alginate is a hydrophilic colloid. When the sodium alginate composite film is in contact with water or aqueous solution, its matrix structure will change. Therefore, isooctane was selected as the food simulant in this experiment. The film, weighing about 2 g, was immersed in 1 L of isooctane solution at 20 ◦C. A total of 1 mL solution was taken out from the food simulation solution at certain intervals (1 mL of isooctane solution was supplemented after taking it out), and the content of CIN in the solution was measured by a dual-beam UV-Vis spectrophotometer with a wavelength of 279 nm. At the same time, SA/CIN and SA/T-HNTs-CIN corresponding film without CIN were used as controls, and three parallel films were set for each sample. The cumulative release rate of CIN in the film can be calculated by Equation (2).

$$\mathbf{C}\left(\%\right) = \left(\mathbf{C} \times \mathbf{V} \times \mathbf{k} / \mathbf{C}\_0 \times \mathbf{m}\right) \times 100\tag{2}$$

where C is the cumulative release rate of CIN (%), C is the concentration of CIN in isooctane at t (mg/mL), V is the volume of isooctane solution (mL), k is the dilution factor of the solution, C0 is the initial concentration of CIN (mg/mL), and m is the amount of film (mg).

#### *2.12. In Vitro Antibacterial Activity of the Film in the Release Experiment*

In order to assess the antimicrobial properties of the manufactured film, a slight modification of the previous method was used [26]. *Staphylococcus aureus* (*S. aureus*) and *Escherichia coli* (*E. coli*) (both of which were provided by the Microbiology Laboratory of the Faculty of Agriculture and Food Engineering, Kunming University of Science and Technology, Yunnan, China) were stored at −80 ◦C. The specific operation process of the antibacterial experiment was as follows. First, the long-term stored *S. aureus* and *E. coli* were inoculated with tryptic soy broth (TSB) medium. This step was then repeated to activate the activity of both strains. Then, 100 μL of the activated bacterial solution was added to a 10 mL TSB medium containing 0.2 g of sample, so that the bacterial solution concentration in the medium was about 10<sup>5</sup> CFU/mL. Subsequently, the bacterial solution containing the sample was cultured on a shaker for 12 h, the temperature was set to 37 ◦C, and the speed was 180 rpm. After the time was up, the bacterial liquid was evenly diluted and spread in tryptic soy agar medium and placed in an incubator at 37 ◦C. After 18–24 h of colony culture, the number of colonies was calculated. In particular, the sample was regularly taken out of the food simulant and wiped dry for the antibacterial test during the release experiment. Each sample was repeated for three times.
