Evaluation of stored lamb bio-preserved using a three-strain cocktail of Lactobacillus sakei

Abstract

Commercially prepared lamb was stored at −1.5 °C after inoculation with a combination of three Lactobacillus sakei strains previously shown to inhibit spoilage and pathogenic bacteria of importance to the meat industry. Between 6 and 14 weeks storage samples were evaluated for growth of inoculated strains, production of fermentation end-products and sensory acceptance of the cooked product. All three L. sakei strains flourished during storage, formed consistently dominant populations and were associated with lower surface pH and increased levels of lactic and acetic acids. Inoculated samples were determined to be as equally acceptable for smell, acidity, rancidity and overall liking as un-inoculated controls.

Introduction

A significant proportion of fresh meat produced in New Zealand is exported as vacuum-packaged chilled product that can spend up to 8 weeks travelling to overseas markets. During storage a range of bacterial populations can develop from small numbers of psychrotrophic organisms acquired by meat surfaces during processing. Typically, such populations tend to develop from the uncontrolled but fortuitous acquisition of benign strains of lactic acid bacteria (LAB) resulting in a wide degree of variability in the microflora of individual packs (Jones, 2004). During processing undesirable contaminants may also be acquired and these can contribute towards spoilage when organisms such as Brochothrix thermosphacta and gas-producing species of clostridia are involved (Broda et al., 1999, Gardner, 1981). The presence of such pathogens as Listeria monocytogenes, Campylobacter jejuni and toxigenic strains of Escherichia coli are also of concern for public health and market access reasons (Anonymous, 2000, Bosilevac et al., 2007, Dykes and Moorhead, 2001, Stern, 1981). Pro-active seeding of fresh meat with small numbers of inhibitory LAB “bio-preservation” offers both a way to improve the microbial consistency of product while reducing the opportunity of unwanted organisms to survive using a range of mechanisms including the production of inhibitory molecules such as bacteriocins (Jones et al., 2009, Kostrzynska and Bachand, 2006, Vermeiren et al., 2006).

Lactobacillus sakei is a meat adapted LAB species commonly isolated from stored products (Chaillou et al., 2005). In a recent study (Jones et al., 2009) the ability of three L. sakei strains (27, 44 and 63) to dominate the microflora of stored meat and inhibit the development of one or more of L. monocytogenes, C. jejuni and Clostridium estertheticum was demonstrated. To be useful for bio-preservation, such strains must also be able to develop on stored meat without detracting from the overall eating quality of the finished product (Stiles, 1996). In this report experiments performed to evaluate the microbiological profile and sensory acceptance of chill-stored vacuum-packaged lamb after treatment with a cocktail of three L. sakei strains are described.