Development of antimicrobial nanoemulsion edible coating of xanthan gum incorporated with pomelo peel extract for cheese preservation

Abstract

The increasing demand for natural food preservation highlights the potential of plant-based edible coatings. This study developed an active nanoemulsion edible coating using xanthan gum (XG) infused with pomelo peel extract (PPE) for paneer preservation. Pomelo peel extracts prepared using methanol, hexane, and dichloromethane showed methanol extract had the highest phenolic (177.06 ± 0.08 mg GAE/g), flavonoid (19.20 ± 0.12 mg RU/g), and antioxidant activity (70.49 ± 0.23 % DPPH inhibition). Antimicrobial activity was confirmed against spoilage organisms, with the highest inhibition zones for Shigella boydii (28.3 ± 1.1 mm), Bacillus cereus (27.6 ± 0.5 mm), and Rhizopus stolonifer (23 ± 2 mm). The nanoemulsion (1.5 % Tween 80, 0.2 % XG, 2 % PPE) was applied to paneer, significantly reducing microbial counts (yeast and mold: 3.31 ± 0.04 log₁₀ CFU/mL; total plate: 3.52 ± 0.01 log₁₀ CFU/mL) over 15 days at 4 °C. It also reduced weight loss (9.62 ± 0.47 %), maintained pH (4.53 ± 0.2), limited lipid hydrolysis (0.81 ± 0.09 %), and preserved acidity (0.99 ± 0.06 %) and sensory quality. This approach supports sustainable food preservation and citrus peel valorisation.

Keywords: Active nanoemulsion; Cottage cheese; Edible coatings; Pomelo peel extract; Shelf-life extension; Waste valorisation.

Fig. 1

Physiochemical analysis of PPE extracted using methanol, hexane, and dichloromethane as solvents: (A) Total phenolic content (TPC), expressed as mg gallic acid equivalents (GAE)/g dry extract (20–100 mg/mL); (B) Total flavonoid content (TFC) expressed as mg rutin equivalents (RU)/g dry extract (20–100 mg/mL); (C) DPPH radical scavenging activity (%) at 20–100 μg/mL. Different letters (a-o) indicate significant difference (p < 0.05) between the solvents at the same concentration. Data are presented as mean ± standard deviation (n = 3).

Fig. 2

Antibacterial and antifungal activity of PPE. (A) Representative agar diffusion plates showing zones of inhibition against six bacterial strains: P. aeruginosa, E. faecalis, E. coli, V. cholerae, B. cereus, S. boydii. and three fungal strains: F. oxysporum, C. albicans, R. stolonifer (B) Quantitative comparison of antibacterial activity between PPE and the positive control. (C) Quantitative comparison of antifungal activity between PPE and the positive control. Different letters (a-d) indicate statistically significant differences (p < 0.05) between the extract and positive control for the same pathogen. Data are presented as mean ± standard deviation (n = 3).

Fig. 3

Antibacterial and antifungal activity of the PP-NE against six bacterial strains: P. aeruginosa, E. faecalis, E. coli, V. cholerae, B. cereus, S. boydii, and three fungal strains: F. oxysporum, C. albicans, R. stolonifer (A) Graphical representation of antibacterial activity at different nanoemulsion concentrations (0.5–5 %) compared with positive control (ampicillin). (B) Graphical representation of antifungal activity at different nanoemulsion concentrations (0.5–5 %) compared with positive control (fluconazole). Different letters (a-h) indicate statistically significant differences (p < 0.05) among the nanoemulsion concentrations and positive control within the same pathogen. Different letters (A-T) indicate statistically significant differences (p < 0.05) among the different pathogens with nanoemulsions concentrations and positive control. Data are presented as mean ± standard deviation from three independent experiments (n = 3).

Fig. 4

Field emission scanning electron microscopy (FE-SEM) images of freeze-dried pomelo peel nanoemulsion (PP-NE): (A) microstructure at 2000× magnification with a scale bar of 5 μm; (B) at 500× magnification with a scale bar of 10 μm; (C) at 100× magnification with a scale bar of 100 μm.

Fig. 5

Changes in the visual appearance of ICC/ paneer during refrigerated storage.

Fig. 6

Physicochemical characterization of coated and control ICC/paneer during storage under refrigerated conditions: (A) Weight Loss; (B) pH; (C) Free fatty acid (FFA) content; (D) Titrable acidity (%), measured at 3-day intervals. Data represent mean ± standard deviation (n = 3).

Fig. 8

Microbial analysis of coated and control ICC/ paneer during storage under refrigerated conditions (A) Total plate count (TPC), (B) Total yeast and mold count (YMC). Data are expressed as mean ± standard deviation (n = 3).

Fig. 7

Sensory evaluation of coated and control ICC/ paneer during storage under refrigerated conditions based on appearance, flavor, color, texture, and overall acceptance. Different letters (A–G) indicate significant differences (p < 0.05) between different treatments across storage days. Data are expressed as mean ± standard deviation (n = 3).