Anti-listeria activity of poly(lactic acid)/sawdust particle biocomposite film impregnated with pediocin PA-1/AcH and its use in raw sliced pork

Highlights

• PLA/SP film coated with pediocin PA-1/AcH exhibits anti-listeria activity.

• Sawdust particle plays an important role in embedding pediocin into PLA film.

• Dry-heating of film before coating with pediocin enhances pediocin adsorption.

• PLA/SP + Ped film reduces listerial population on chilled pork up to 99%.

Abstract

A novel poly(lactic acid) (PLA)/sawdust particle (SP) biocomposite film with anti-listeria activity was developed by incorporation of pediocin PA-1/AcH (Ped) using diffusion coating method. Sawdust particle played an important role in embedding pediocin into the hydrophobic PLA film. The anti-listeria activity of the PLA/SP biocomposite film incorporated with Ped (PLA/SP + Ped) was detected, while no activity against the tested pathogen was observed for the control PLA films (without SP and/or Ped). Dry-heat treatment of film before coating with Ped resulted in the highest Ped adsorption (11.63 ± 3.07 μg protein/cm²) and the highest anti-listeria activity. A model study of PLA/SP + Ped as a food-contact antimicrobial packaging on raw sliced pork suggests a potential inhibition of Listeria monocytogenes (99% of total listerial population) on raw sliced pork during the chilled storage. This study supports the feasibility of using PLA/SP + Ped film to reduce the initial load of L. monocytogenes on the surface of raw pork.

Introduction

Listeria monocytogenes is a foodborne pathogen that causes a severe disease called listeriosis (Alves et al., 2006, Gialamas et al., 2010). L. monocytogenes has been listed in the top five highest ranking pathogens with respect to the total case of food-borne illnesses in the United States (Theinsathid et al., 2012) and is a major concern in food industries (Farber and Peterkin, 1991). This pathogenic bacterium is of major concern in a wide variety of foods, especially in chilled meat and ready-to-eat (RTE) meat products due to its ability to survive and grow at refrigeration temperatures (Schlech, 2000, Ye et al., 2008a, Ye et al., 2008b). In order to reduce healthy risk for the consumer from L. monocytogenes, criteria or recommendations for tolerable levels of L. monocytogenes in processed foods have been established. The USA and Thailand practice “zero tolerance”, while Canada and France apply different norms according to the foodstuff (Thévenot et al., 2006).

To guarantee food safety through the inhibition of L. monocytogenes, the use of bacteriocins and other biologically derived antimicrobials with anti-listeria activity in packaging material have received a considerable attention (Coma, 2008, Lara-Lledó et al., 2012, Min et al., 2010, Sánchez-González et al., 2013). Thus, during the last decades, innovative bioactive films enriched with bacteriocins have been developed. The most-commonly studied antimicrobial agents for applications in this sense are nisin (Cao-Hoang et al., 2010, Guiga et al., 2010, Hoffman et al., 2001, Janes et al., 2002, Jin et al., 2009, Ko et al., 2001, McCormick et al., 2005, Neetoo et al., 2008, Scannell et al., 2000), pediocin PA-1/AcH (Ming et al., 1997, Santiago-Silva et al., 2009), and enterocin (Iseppi et al., 2008, La Storia et al., 2012). Among these bacteriocins, nisin and pediocin PA-1/AcH are the only bacteriocins, to date, that have been approved for use in food. Although anti-listeria efficiency of nisin and pediocin significantly differed depending on the producing or indicator strains, the sample preparation method, and the bacteriocin assay conditions, pediocin is likely to have higher activity and acts more specifically against L. monocytogenes than nisin (Cintas et al., 1998, Rodriguez et al., 2002). In addition, pediocin PA-1, in contrast to both nisins A and Z, has potential to inhibit Listeria without disturbing other bacteria including beneficial ones (Blay et al., 2007).

Due to a trend toward active and green packaging, the use of bio-materials including cellulose, starch, pectin and poly(lactic acid) (PLA) have been more emphasized (Kuorwel et al., 2011, Liu et al., 2009, Rodriguez et al., 2006, Theinsathid et al., 2012). PLA is recognized as compostable biopolymer that attracts the interest for the packaging industry because of its outstanding properties and earth-friendly biodegradability. PLA exhibits many properties that are equivalent to or better than many petroleum-based plastics (Liu et al., 2009). Importantly, PLA packaging can be produced by many manufacturing processes, such as film blowing, injection molding, sheet extrusion, blow molding and thermoforming (Imam et al., 2008, Jamshidian et al., 2010). The combination of biodegradability of PLA with antimicrobial property of pediocin against a wide broad spectrum of food pathogen will be of full benefit as the active packaging. As a consequence, health-risk of consumers can be reduced. Shelf-life can be extended, thereby lowering the economic loss. Importantly, the waste of post use of this packaging will be decomposed through compostable system without causing environmental waste problems.

However, direct incorporation of antimicrobial peptide to PLA film has been limited by the hydrophobic characteristics of PLA. The incompatibility of bacteriocin in hydrophobic polymers caused the phase separation in film, leading to poor antimicrobial activity and mechanical properties. To solve this problem, sawdust particle (SP), a low-water solubility hydrophilic particle, was incorporated in PLA film to enhance adsorption of pediocin using diffusion coating technique. In contrast to the large amount of information on the antimicrobial activity of packaging films containing antimicrobials, to our knowledge no information is available about using natural fiber as carrier of pediocin PA-1/AcH in PLA film. Research on the possibility of using sawdust particle would lead to an alternative natural preservation method, easily applicable and of low cost. In addition, effect of pre-conditioning methods was also investigated to enhance the pediocin adsorption. Finally, anti-listeria activity of the PLA/SP biocomposite film toward a model pork system was determined in order to ensure the potential use of the film in real food system.