Marinated meat and fish products have in recent years gained popularity. Marinades have been added to provide flavour and in some cases tenderness but they have rarely been associated with prolonged shelf-life.
The objective of this study was to enhance the microbial stability of marinated meat and fish products. Several preserving techniques were evaluated, including natural antimicrobials, innovative packaging and protective cultures.
A characterization of the bacterial spoilage flora in marinated pork meat showed that the flora at the end of the storage time depended on the quality of the raw material and on the production environment. There was no correlation between the type of marinade that was used and the bacterial flora. Several bacterial strains were isolated and tested for their spoilage potential and odour evaluations showed that strains of Lactobacillus algidus and Leuconostoc mesenteroides promoted the development of off-odours.
Several natural preservatives, including thymol, cinnamaldehyde, allyl isothiocyanate (AIT), citric acid, ascorbic acid, a rosemary extract and a grapefruit seed extract were tested for their antimicrobial activity against a range of spoilage and non-spoilage bacteria isolated from marinated pork. All compounds except ascorbic acid showed antibacterial effect in a microplate model system and several synergistic effects were observed, especially between organic acids and thymol or AIT. However, when antimicrobials were added to pork meat at concentrations that inhibited bacterial growth in the plate assay, no growth inhibition was observed. As even higher concentrations showed no effect in the meat, the use of these natural antimicrobials alone to prolong the shelf-life of vacuum-packed meat is believed to be of no practical use in marinated meat, at least under the chosen conditions.
The effect of organic acids in combination with a dissolving CO2 headspace was evaluated in a novel packaging system. Results showed that combinations of 1 % acetic acid and 3 % citric acid in a brine solution and CO2 (initial gas / product ratio 0.2 / 1.0) inhibited the bacterial growth in fresh salmon. CO2 dissolved completely in the product, yielding a product with the outer appearance of a vacuum package. While each treatment alone inhibited bacterial growth, the effect was enhanced when all three treatments were combined. Corresponding experiments with pork meat showed the same bacterial inhibition. However, while the outer appearance of salmon was not altered by the addition of acids and CO2, pork samples containing citric acid showed significant precipitation in the package. As a result, 3 % citric acid at pH 5 may not be applicable in pork meat, at least not in clear marinades.
Three strains of Leuconostoc carnosum, two isolates from marinated pork and one commercial protective culture were evaluated as protective cultures to inhibit the growth of the specific spoilage organisms (SSO’s) Lact. algidus and Leuc. mesenteroides. All three strains alone and in combination inhibited the growth of these spoilage bacteria. Although the commercial strain showed highest inhibition in an agar overlay model, the two pork isolates grew faster in the meat and thereby showed greater inhibition of SSO growth in pork.
In conclusion, the use of innovative packaging methods with CO2 in combination with natural preservatives (organic acids) showed efficient growth inhibition of specific spoilage bacteria in marinated salmon and pork. Plant-derived antimicrobials alone were not able to prolong the shelf-life of marinated meat at sensorically acceptable concentrations. The use of pork-derived lactic acid bacteria as protective starter cultures showed promising results in inhibiting specific spoilage bacteria in pork.