*2.1. Sample Collection*

The samples of *Spondias mombin* were collected in the early summer season from the local market of the Dinajpur (Latitude: 25.6221◦ N, Longitude: 88.6438◦ E, and Altitude: 42.0 m), Mymensingh (Latitude: 24.7471◦ N, Longitude: 90.4203◦ E, and Altitude: 19.0 m), Barishal (Latitude: 22.7010◦ N, Longitude: 90.3535◦ E, and Altitude: 1.22 m), Rajshahi (Latitude: 24.3745◦ N, Longitude: 88.6042◦ E, and Altitude: 18.0 m), and Pabna districts (Latitude: 24.0023◦ N, Longitude: 89.1413◦ E, and Altitude: 19.0 m) of Bangladesh. Three separate samples were collected from each district, which were treated as three replications. The microorganism species used in this study were bacteria (ATCC) such as *Escherichia coli*, *Salmonella* spp., *Staphylococcus aureus*, and fungi such as *Aspergillus niger* and *Penicillium oxalicum*. The pure cultures of these species were obtained from the Laboratory of Microbiology, Hajee Mohammad Danesh Science and Technology University (HSTU), Dinajpur, Bangladesh. The cultures of each microorganism were inoculated on nutrient agar (NA) and Sabouraud dextrose agar (SDA) (Merck KGaA, 64271 Darmstadt, Germany) at 37 ◦C for 24 h, and stored at less than 4 ◦C.

### *2.2. Preparation of Hog Plum Peel Powder*

The samples were washed and rinsed with deionized water and subsequently peeled with a knife carefully. The peels of each of the five samples were weighted and spread in five different trays for drying in a cabinet dryer (Model FMA-275) at 60 ◦C for three days until they were completely dehydrated. Then the samples were taken out from the drier and put into desiccators for a few minutes to adjust to the ambient temperature. Then, the dried samples were blended by an electric blade blender (Vitamix 5200 Series) to make the powdery form and to prepare the peel samples for hydro-distillation.

### *2.3. Extraction of Essential Oil*

Five samples of hog plum peels were collected in mid-June 2018 from the five districts. Each sample of peel powder, weighing 20 g, was suspended in 300 mL of deionized water and subjected to steam distillation using a Clevenger-type apparatus for 4 h. Then the sample oils were collected, dried over anhydrous sodium sulfate (Na2SO4), filtered, and stored in sealed vials under refrigeration at 4◦C until analysis [29]. The yield (%) of oil was calculated by the following formula:

> Yield (%) = (Weight of oil)/(Weight of the fresh sample) × 100

### *2.4. Gas Chromatography and Mass Spectrometry (GC-MS) Analysis*

GC-MS was conducted with a Varian Saturn 2200 equipped with an ion trap detector (ITD) for the identification of different components of essential oil. To obtain better results, dichloromethane was used as solvent. The sample of 2.0 μL was injected on a DB-5 MS (30 m, 0.25 mm ID, 0.25 μm film thickness) column. Helium was used as a carrier gas with a flow rate of 1 mL/min and a split ratio of 1:5. The temperature in the oven-dryer was set at 50 ◦C for 1 min, followed by a temperature gradient of 2.5 ◦C/min to 280 ◦C/min for 40 min. The injector and transfer line temperatures were set to 250 ◦C and 280 ◦C, respectively. Various components were identified by their retention time (5.52–22.34 min) and peak enhancement with standard samples in gas chromatographic mode and a National Institute of Standards and Technology (NIST 20) library search from the derived mass fragmentation pattern of various components of the essential oil [30].

### *2.5. Determination of Antimicrobial Activity*

The antimicrobial activity of the tested essential oil was monitored using the disc diffusion method [31] against different food-borne pathogens including bacteria (*Escherichia coli*, *Salmonella* spp., and *Staphylococcus aureus*), and two selected fungi (*A. niger* and *P. oxalicum*). The antibacterial and antifungal screening was performed briefly using ciprofloxacin (10 μg/disc) and fluconazole (10 μg/disc) as a positive control and sterile water as a negative control. Standard culture media of each type of bacteria and fungi were employed on NA and SDA plates (100 mL each), where 5 μL (1000 ppm) of the essential oil was used for each test sample. During the investigation, the incubation temperature was maintained for both fungi (25 ◦C) and bacteria (37 ◦C). The zones of inhibition thus developed against the tested microorganisms were measured after a period of 48 and 96 h. All experiments were conducted in triplicate. The results of the antimicrobial activity of the peel oil against the different microorganisms were expressed as resistant, intermediate, and sensitive.
