Inhibition by Lactobacillus sakei of other species in the flora of vacuum packaged raw meats during prolonged storage

The abilities of five Lactobacillus sakei strains and one Lactococcus lactis strain to retain inhibitory activity against several target organisms in the flora of product during 12 weeks storage of vacuum-packaged lamb and beef was investigated. L. sakei strains were generally found capable of developing dominant populations on both beef and lamb. L. lactis 75 grew poorly on lamb did not inhibit co-inoculated Brochothrix thermosphacta. Lamb inoculated with the Sakacin-A producer L. sakei Lb706 had lower Listeria monocytogenes populations than lamb inoculated with a bacteriocin-negative variant. In beef packs inoculated with Clostridium estertheticum spores and L. sakei strain 27, 44 or 63, the development of blown-pack spoilage was delayed by up to one week. Campylobacter jejuni inoculated onto beef was recovered from fewer packs when it was co-inoculated with 3000 CFU cm⁻² of L. sakei strain 27, 44 or 63. Observed inhibition did not always correlate with inhibition observed in earlier media-based studies, supporting the view that functionality identified using simple media-based screening methods may not be replicated in the complex environment of stored foods, and vice-versa. These findings further define a set of L. sakei strains with potential for the extended bio-preservation of minimally processed fresh beef and lamb.     

Synchronised interrelationship between lipid/protein oxidation analysis and sensory attributes in refrigerated minced beef meat formulated with Punica granatum peel extract

Microbiological, chemical and sensory effects of pomegranate peel ethanol extract (EE) at 0.1, 0.5 and 1% (w w⁻¹) on refrigerated minced beef meat were undertaken. Chemical analyses revealed that the treated meat underwent significant decrease (P < 0.05) of primary and secondary lipid oxidation. By the end of storage, EE at 1% reduced the MetMb, carbonyl group accumulation and the disappearance of sulphydryl proteins by 56.68, 65.71 and 59.69% respectively, compared with control samples. EE at 1% showed also the highest scores for colour, appearance, odour and overall acceptability (OA) attributes using a 9-point hedonic scale. Chemometric approaches showed that lipid/protein oxidation analysis, sensory attributes and storage time allowed the samples discrimination. Oxidative stability parameters were equally used to predict OA by linear regression analysis. The reported data provide an approach to strengthen the interpretation of sensory quality and how they are affected by chemical changes in newly formulated meat products.     

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

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.     

Antifungal activity of lactic and propionic acid bacteria and their potential as protective culture in cottage cheese

Dairy products are very susceptible to fungal spoilage, which causes economic losses and is a public health concern due to the possible production of mycotoxins. Several novel approaches have been proposed to delay the growth of mold in cheese. Among these, adding a protective culture is particularly interesting in view of increasing consumer demand for naturally preserved foods. The aim of this study was to select a new protective culture and validate its effectiveness as an inhibitor of fungal proliferation in cottage-type cheese. Food-grade bacteria (88 strains) were screened for inhibition of four spoilage molds commonly isolated from cheese. Strains of Propionibacterium and Lactobacillus were the most active. Seven strains were selected and tested further, alone and in pairs, for their abilities to prevent Penicillium chrysogenum growth in a solidified dairy matrix and in cottage cheese. Lactobacillus rhamnosus A238 alone or in combination with Bifidobacterium animalis subsp. lactis A026 inhibited mold growth for at least 21 days at 6 °C, due probably to the production of secondary metabolites and/or competition for nutrients. Overall, our findings show that these strains inhibit molds, some of them acting in synergy, and have potential for use as bio-preservatives in fresh cheese.     

Comparison of different application strategies of divergicin M35 for inactivation of Listeria monocytogenes in cold-smoked wild salmon

Cold-smoked salmon treated with divergicin M35-producing Carnobacterium divergens M35, C. divergens ATCC 35677 (a non-producer of bacteriocin), purified divergicin M35 or supernatants of C. divergens M35 culture in snow crab hepatopancreas (SCH) medium or MRS broth was challenged with Listeria monocytogenes (up to 10³ CFU/g). Samples were stored at 4 °C for up to four weeks. L. monocytogenes, total bacterial and lactic acid bacterial counts were determined along with changes in total volatile base nitrogen (TVBN) and biogenic amine production as well as texture, color and odor. A 2.6 log CFU/g reduction in L. monocytogenes was obtained for up to 10 days of storage in samples treated with C. divergens M35. Purified divergicin M35 (50 μg/g), SCH supernatant or MRS supernatant brought reductions of 1 log CFU/g at the beginning of storage. However, the anti-listerial activity of the supernatants lasted for 15 days compared to 3 days for purified divergicin M35. Color and texture were affected little in samples containing C. divergens M35 compared to un-inoculated samples. TVBN and biogenic amine production, particularly tyramine, remained below the maximum acceptable level in fish appreciation. These results clearly show the potential of C. divergens M35 culture as well as divergicin M35 bio-ingredient for application to the inactivation of L. monocytogenes in ready-to-eat seafood.     

Antilisterial activity of lactic acid bacteria isolated from "Alheiras" (traditional Portuguese fermented sausages): In situ assays

A total of 226 lactic acid bacteria (LAB) isolated from “Alheira”, a traditional Portuguese fermented sausage, were screened for antagonistic activity against some pathogenic microorganisms, including Listeria monocytogenes. The objective was to isolate LAB with antibacterial activity from “Alheiras” and to select strains that could be used in “Alheira” production. Isolates displaying antibacterial activity against Listeria innocua and L. monocytogenes were investigated for the nature of the antibacterial compounds active against these microorganisms. Results showed that two LAB cultures retained activity in the supernatants after neutralization and catalase treatment. These two strains were both identified as Pediococcus pentosaceus. The final aim of this work was to test the antilisterial activity of these two strains during storage of “Alheira mass” (sterilized), at 4 °C. The growth of L. innocua population was significantly suppressed in the paste of “Alheira” when the samples were co-inoculated with the LAB strains, in comparison with the paste only inoculated with L. innocua or co-inoculated with a bacteriocin negative strain of Ped. pentosaceus (ca. 1 × 10⁷ CFU/g after 28 days of incubation).     

Isolation of lactic acid bacteria with inhibitory activity against pathogens and spoilage organisms associated with fresh meat

The use of lactic acid bacteria (LAB) as protective cultures in vacuum-packed chill-stored meat has potential application for assuring and improving food quality, safety and market access. In a study to identify candidate strains suitable for evaluation in a meat model, agar-based methods were employed to screen 181 chilled meat and meat process-related LAB for strains inhibitory to pathogens and spoilage organisms of importance to the meat industry. Six meat-derived strains, including Lactobacillus sakei and Lactococcus lactis, were found to be inhibitory to one or more of the target strains Listeria monocytogenes, Brochothrix thermosphacta, Campylobacter jejuni and Clostridium estertheticum. The inhibitory agents appeared to be either cell-associated or molecules released extracellularly with bacteriocin-like properties. Variations detected in the antimicrobial activity of LAB associated with changes to test parameters such as substrate composition underlined the importance of further in situ evaluation of the inhibitory strains in stored meat trials.