Slow-release antibacterial film loaded with clove essential oil based on tapioca starch used for bread preservation

Abstract

White pollution is an increasingly serious concern. Consequently, the development of green degradable packaging materials has become a research focus. We incorporated different concentrations of clove essential oil (Ceo) (0 %, 0.5 %, 0.75 %, 1.0 %, and 1.25 %, w/w) into modified tapioca starch to formulate bacteriostatic compound films. The test results indicated that the barrier properties of the Ceo-series composite films surpassed those of the tapioca starch (TS) film. Specifically, the oxygen permeability of the 1.25 % Ceo film was 7.31 g/m²·s, the water vapor permeability decreased to 1.35 g/m²·s, and the oil permeability was reduced to 0.15 g mm m^-2 d^-1. In addition, the 1.25 % Ceo film exhibited inhibition zones of 4.23 ± 0.28 mm against Staphylococcus aureus and 5.02 ± 0.31 mm against Escherichia coli. In the sustained release test, the Ceo-series composite films demonstrated a uniform and stable release. Furthermore, their degradability reached approximately 70 % by the 20th day. The 1.25 % Ceo film extended the shelf-life of bread to 9 days, exceeding than that of the commercially available polyethylene (PE) plastic wrap. These results highlight that Ceo-series composite films possess outstanding characteristics as active food packaging materials, particularly for noncontact food preservation.

Keywords: Antibacterial; Clove essential oil; Green packaging; Noncontact preservation; Slow-release film; Starch-based film.

Graphical abstract

Fig. 1

Rheological properties of different film solutions. (A) Shear stress as a function of shear rate (0–300 s⁻¹); (B) shear stress as a function of shear rate (300–0 s⁻¹); (C) apparent viscosity as a function of shear rate (0–300 s⁻¹); (D) apparent viscosity as a function of shear rate (300–0 s⁻¹).

Fig. 2

(A) Thermogravimetric analysis (TGA); (B) derivative thermogravimetry (DTG); (C) water vapor permeability (WVP) of composite films; (D) oxygen permeability (OP) of composite films; (E) oil permeability (P_O) of composite films; (F) cytotoxicity evaluation of the 1.25 % CeO composite film. Vertical bars represent the standard deviation (mean ± SD, n = 3). Different lowercase letters indicate statistically significant differences (P < 0.05).

Fig. 3

Release of composite films in different simulated liquids. (A) In nonacidic food simulation solution (10 % ethanol, solution) at 4 °C; (B) in oil-in-water solution food simulation solution (50 % ethanol solution) at 4 °C; (C) in fatty food simulation solution (95 % ethanol solution) at 4 °C; (D) in nonacidic food simulation solution (10 % ethanol solution) at 25 °C; (E) in oil-in-water solution and alcoholic food simulation solution (50 % ethanol solution) at 25 °C; (F) in fatty food simulation solution (95 % ethanol solution) at 25 °C. Vertical bars represent the standard deviation of the mean (n = 3).

Fig. 4

(A) Bacteriostatic zone; (B) diameter of the bacteriostatic zone (mm); (C) scanning electron microscopy of bacteria (scale bars: 1 μm). Vertical bars represent the standard deviation of the mean (n = 3); different letters represent significant differences (P < 0.05).

Fig. 5

(A) Morphological changes of the composite films during the 20-day degradation process; (B) scanning electron microscopic images of the composite films after 20-day degradation (scale bars: 200 μm, 20 μm). Vertical bars represent the standard deviation of the mean (n = 3); different letters represent significant differences (P < 0.05).

Fig. 6

(A) The visual appearance changes of bread with different treatments during 12 days of storage; (B) total number of colonies in bread during the 12-day preservation process.

Fig. 7

Changes in moisture content of bread packaged with different composite films (PE film, DM film and 1.25 % Ceo film) during 12-day storage.