2.3.2. Disc Diffusion Assay

Paper disc agar plate assays were used to determine the antimicrobial activities of eighteen EOs against ST, SA, LM, and EC O157:H7 [33]. The bacterial suspension of 8 log cfu/mL was uniformly spread on a TSA plate. Sterile filter paper discs (6 mm) impregnated with EOs of 5 μL were placed on the surface of the TSA plate. After 24 h of incubation at 37 ◦C, the inhibition zone diameter (mm) on the TSA plate was measured. Inhibition zones were classified according to size as low (<12 mm), moderate (12–20 mm), and strong (≥20 mm) [34]. Three measurements were taken to determine the average results.

### 2.3.3. Determination of the Minimal Inhibitory Concentration (MIC)

The MIC was determined using a modified method [35]. Briefly, EOs were mixed in dimethylsulfoxide (DMSO, 0.8% *v*/*v*) (Kemiou, Tianjin, China) and added into the tube containing TSB using a two-fold dilution method (10 to 0.0195 μL/mL) [36]. Then, 100 μL bacterial suspensions (5 log cfu/mL) were respectively added to each tube. The MIC was determined after enrichment by measuring the turbidity of the culture media.

### *2.4. Preparation of Chitosan Edible Coating*

The chitosan EC was prepared by mixing 2% (*w*/*v*) chitosan (food-grade, 50 KD, Henan Qiang Li Chemical Products Co., Ltd., Zhengzhou, China), 1.5% (*w*/*v*) glycerol, and 2% (*w*/*v*) calcium chloride solution (food-grade) containing 1% (*w*/*v*) ascorbic acid (food-grade) and 1% (*w*/*v*) citric acid (food-grade) in ultrapure water and stirred at 70 ◦C until the solution became transparent [28,37]. Citric acid and ascorbic acid were mixed into chitosan EC as both antioxidants and colour fixatives. Cinnamon oil was incorporated into chitosan EC at different concentrations (0.2%, 0.4%, and 0.6% *v*/*v*). Homogenisation of the final solutions was achieved at 12,500 rpm for three minutes using an Ultra Turrax T25 mixer (IKA® WERKE, Staufen, Germany).

### *2.5. Processing and Packaging of Fresh-Cut Potatoes*

The surface of fresh potatoes was sterilised with 75% (*v*/*v*) alcohol after washing. The sample was air-dried inside a biosafety cabinet for 10 min at 25 ◦C. Potato cubes (1 cm3) were prepared using a sterile knife. Samples were soaked in chitosan solution for two minutes. Samples coated with chitosan EC or chitosan EC containing cinnamon oil of 0.2%, 0.4%, and 0.6% were subsequently assessed. Uncoated potatoes were evaluated as a control. For 16 days at 4 ◦C, the fresh-cut potatoes were packaged on polystyrene trays (255 mL) wrapped in PVC films.

### *2.6. Determination of Potato Colour, Weight Loss, and Firmness*

2.6.1. Colour

The colour parameters of potato cubes, including *L*\* (lightness), *a*\* (+*a*\* = redness, −*a*\* = greenness), and *b*\* (+*b*\* = yellowness, −*b*\* = blueness), were detected using a CR400/CR410 colorimeter (Minolta, Tokyo, Japan) [38]. The experiments were conducted in triplicate.

### 2.6.2. Weight Loss

Potato cubes were placed on polystyrene trays and weighed using a digital balance (PL-2002, METTLER TOLEDO, Greifensee, Switzerland) during storage [39]. The weight loss rate equation is given by Equation (1):

$$\text{Weight loss rate (\%)} = \text{[(m}\_1-\text{m}\_2)/\text{m}\_1\text{]} \times 100\tag{1}$$

where m1 is the initial weight (g), and m2 is the weight at the specified time point (g).

### 2.6.3. Firmness

The firmness of potato cubes was measured using a TA.XT texture analyser (Stable Micro Systems Ltd., Godalming, UK). We measured the firmness of the cube based on the force (N) exerted on the slices in triplicates using the compression probe P5 (5 mm diameter), at a speed of 1.0 mm s<sup>−</sup>1, and a penetration distance of 8 mm [40]. Each sample was duplicated three times.
