Characterization and coating application of composite gelatin packaging containing eucalyptus leaf essential oil liposome and phage endolysin for preservation of pacific white shrimp (Penaeus vannamei)

Abstract

Shrimp are highly susceptible to spoilage during cold storage because of microbial growth and lipid oxidation. This study presents the development and characterization of a novel composite gelatin packaging that incorporates eucalyptus leaf essential oil liposome (EEOL) and phage endolysin (rLys). It also assesses the effectiveness of coating application for shrimp preservation to provide an effective strategy. The addition of EEOL and rLys to gelatin packaging not only enhanced film flexibility (13.16%–13.42%) and reduced oxygen permeability (0.95-0.96 × 10⁻⁷ g m⁻¹·s⁻¹), but also endowed the films with antioxidant (DPPH radical scavenging rate of 67.14%–67.28%) and antimicrobial properties (complete inhibition at low titers and a reduction of 3.00–4.05 log₁₀ CFU/mL at high titers). In the shrimp coating preservation experiment, the quality of untreated shrimp started to deteriorate on the 3rd day. In contrast, the pH values, total volatile base nitrogen (TVB-N) content, and total viable count (TVC) of shrimp with the composite coatings on the 7th day were 7.28, 154.02–175.08 mg/kg, and 4.34–5.34 log₁₀ CFU/g, respectively, remaining within the limits of the Chinese national standard. Moreover, the release of EEOL from the composite coatings led to thiobarbituric acid values (TBA) of 0.19–0.21 mg malondialdehyde (MDA)/kg on the 5th and 7th day, respectively. Additionally, rLys in the coating significantly decreased the numbers of Escherichia coli O157:H7 and Salmonella enteritidis in the shrimp body by 1.04–1.06 log₁₀ CFU/g and 1.13–1.14 log₁₀ CFU/g, respectively. These results suggest that the synergistic effect of EEOL and rLys in composite gelatin coating, especially the Ge-EEOL-rLys₆₀, can extend the preservation period of shrimp to 5 d or even longer, thereby providing the possibility of maintaining shrimp freshness and safety.