Covalent Immobilization of Polypeptides on Polylactic Acid Films and Their Application to Fresh Beef Preservation

Abstract

To enhance the advantage of a long-term stability and low-toxicity active packaging system, two biodegradable covalent immobilized antibacterial packaging films were developed and applied to fresh beef preservation in this study. A polylactic acid (PLA) film was prepared by the extrusion-casting method. The surface of the PLA film was modified with plasma treatment to generate carboxylic acid groups, and then antibacterial agent nisin or ε-poly lysine (ε-PL) was covalently attached to the modified film surface. Physical, chemical, and antimicrobial properties of films were then characterized. Scanning electron microscopy and water contact angle images confirmed that nisin or ε-PL was successfully grafted onto the film surface. The values of protein loading on the nisin−g−PLA film and ε-PL−g−PLA film were 5.34 ± 0.26 and 3.04 ± 0.25 μg of protein/cm 2 on the surface. Microbial analysis indicated that the grafted films effectively inhibit the growth of bacteria. Finally, the effects of the nisin−g−PLA film or ε-PL−g−PLA film on physicochemical changes and microbiological counts of fresh beef during cold storage at 4 °C were investigated. The total viable count of the control sample exceeded 7 logarithms of the number of colony forming units per gram (log CFU/g) after 11 days of cold storage (7.01 ± 0.14 log CFU/g) versus 15 days for the ε-PL−g−PLA film (7.37 ± 0.06 log CFU/g) and the nisin−g−PLA film (6.83 ± 0.10 log CFU/g). The results showed that covalent immobilized antibacterial packaging films had positive impacts on the shelf life and quality of fresh beef. Therefore, a covalent immobilized antibacterial packaging system could be a novel preservative method for foods.

Green Coating Polymers in Meat Preservation

“…The results showed that covalent immobilized antibacterial packaging films had positive impacts on the shelf-life and quality of fresh beef. The total viable count of the control sample and ε-PL-g-PLA film/nisin-g-PLA film exceeded 7 log CFU/g on the 11 days and 15 days of cold storage, respectively [52].…”

“…Among the bio-derived materials, PLA (discussed below in Section 2.2) has received a special attention as one of the most attractive short-use packaging materials due to its good transparency, compostability, high rigidity and modulus at room temperature, and lack of ecotoxicity [50,51]. Very briefly and in the objective of enhancing the long-period stability and reduced toxicity of active packaging systems, several strategies were proposed, among which two biodegradable covalent immobilized antibacterial packaging films for fresh beef preservation were investigated [52]. A PLA film was prepared by extrusion casting and the surface of the film was modified with a plasma treatment to generate carboxylic acid groups, then an antibacterial agent nisin or ε-poly-lysine (ε-PL) was covalently attached to the modified film surface.…”

Release of Cinnamaldehyde and Thymol from PLA/Tilapia Fish Gelatin-Sodium Alginate Bilayer Films to Liquid and Solid Food Simulants, and Japanese Sea Bass: A Comparative Study

“…The chemical structures of the FGSA-based layer and PLA from the obtained bilayer films were characterized by FTIR, as shown in Figure 1 c. Typical absorption bands of PLA were recorded in the spectrum: C=O carbonyl stretching (1750 cm −1 ), C−H stretching of −CH 3 (1452 cm −1 and 1382 cm −1 ), C−O stretching (1181 cm −1 and 1081 cm −1 ), and −OH bending (1014 cm −1 ) [ 27 , 28 , 29 ]. The FTIR spectra of all FGSA-based layers showed similar characteristic bands: amide-I (C−O stretching), amide-II (N−H bending), and amide-III (C−N and N−H stretching) with the location of the peaks at approximately 1645 cm −1 , 1552 cm −1 , and 1240 cm −1 in order, as well as a broadband peak around 3287 cm −1 owing to the superposition of the hydroxyl group and the amino group [ 30 , 31 , 32 ].…”

“…The surface hydrophobicity of films was determined through the water contact angle (WCA) parameter according to the method described by Huang et al [ 27 ]. A droplet of distilled water (3 μL) was carefully dropped on the film surface using a microsyringe, and then the contact angles and images were recorded immediately by a JC2000c video-based contact angle meter (Shanghai Zhongchen Digital Technic Apparatus co., Ltd., Shanghai, China)…”

Effects of Processing Conditions and Plasticizing-Reinforcing Modification on the Crystallization and Physical Properties of PLA Films

“…Copolymerization with other monomers is another approach that has been used to improve the properties such as stiffness, permeability, crystallinity, and thermal stability [ 8 , 27 , 28 , 29 ]. Covalent immobilization of polypeptides on PLA films can make it an active packaging [ 30 ]. Adding filler and plasticization was explored as an economically viable way to modify the properties of PLA resin.…”