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Antimicrobial Activity of Oregano Essential Oil Incorporated in Sodium Alginate Edible Films: Control of Listeria monocytogenes and Spoilage in Ham Slices Treated with High Pressure Processing - PubMed

  • ️Tue Jan 01 2019

Antimicrobial Activity of Oregano Essential Oil Incorporated in Sodium Alginate Edible Films: Control of Listeria monocytogenes and Spoilage in Ham Slices Treated with High Pressure Processing

Foteini Pavli et al. Materials (Basel). 2019.

Abstract

The aim of the study was to evaluate the efficacy of oregano essential oil (OEO) incorporated in Na-alginate edible films when applied to sliced ham inoculated with a cocktail of Listeria monocytogenes strains, with or without pretreatment by high pressure processing (HPP). Microbiological, physicochemical and sensory analyses (in Listeria-free slices) were performed, while, the presence/absence and the relative abundance of each Listeria strain, was monitored by pulsed field gel electrophoresis (PFGE). The OEO incorporation in the films, caused approximately 1.5 log reduction in Listeria population at 8 and 12 °C at the end of the storage period, and almost 2.5 log reduction at 4 °C. The HPP treatment caused 1 log reduction to the initial Listeria population, while levels kept on decreasing throughout the storage for all the tested temperatures. The pH of the samples was higher in the cases where HPP was involved, and the samples were evaluated as less spoiled. Furthermore, the presence of OEO in the films resulted in color differences compared to the control samples, whilst the aroma of these samples was improved. In conclusion, the combined application of HPP and OEO edible films on the slices, led to a significant reduction or absence of the pathogen.

Keywords: Listeria monocytogenes; Ready-To-Eat meat, antimicrobial packaging; antimicrobial compounds; non-thermal processing, Infrared spectroscopy; spoilage.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1

Growth curves of the different bacterial populations in ham stored at 4 °C for the control samples (I), samples with edible film free from oregano essential oil- (OEOF) (II) and samples with edible film supplemented with oregano essential oil- OEOS (III), without (a) and after (b) the high pressure processing treatment. (♦) Lactic acid bacteria, (■) lactococci/streptococci and (▲) total viable counts. The bars represent the mean values ± standard deviations.

Figure 2
Figure 2

Growth curves of the different bacterial populations in ham stored at 8 °C for the control samples (I), samples with edible film free from oregano essential oil-OEOF (II) and samples with edible film supplemented with oregano essential oil-OEOS (III), without (a) and after (b) the high pressure processing treatment. (♦) Lactic acid bacteria, (■) lactococci/streptococci and (▲) total viable counts. The bars represent the mean values ± standard deviations.

Figure 3
Figure 3

Growth curves of the different bacterial populations in ham stored at 12 °C for the control samples (I), samples with edible film free from oregano essential oil-OEOF (II) and samples with edible film supplemented with oregano essential oil-OEOS (III), without (a) and after (b) the high pressure processing treatment. (♦) Lactic acid bacteria, (■) lactococci/streptococci and (▲) total viable counts. The bars represent the mean values ± standard deviations.

Figure 4
Figure 4

Survival curves of Listeria monocytogenes cocktail strains in ham stored at 4 °C (I), 8 °C (II) and 12 °C (III), without (a) and after (b) high pressure processing treatment. (♦) Control samples, (■) samples with edible film free from oregano essential oil-OEOF and (▲) samples with edible film supplemented with oregano essential oil-OEOS. Open symbols (◊, □, Δ), indicate absence of Listeria monocytogenes after application of the enrichment method. The bars represent the mean values ± standard deviations.

Figure 5
Figure 5

Changes in pH values for ham slices without (a) and after (b) high pressure processing treatment, during storage at 4 °C (I), 8 °C (II) and 12 °C (III). Values regarding control and OEOF samples (without essential oil), are common with those reported in our previous study [52].

Figure 6
Figure 6

Changes in C* values for ham slices without (a) and after (b) high pressure processing treatment, during storage at 4 °C (I), 8 °C (II) and 12 °C (III). Values regarding control and OEOF samples (without essential oil), are common with those reported in our previous study [52].

Figure 7
Figure 7

Sensory scores for ham slices without and after the high pressure processing treatment, during storage at 4 (upper line), 8 (middle line) and 12 °C (bottom line). The “total” value represents the mean value of aroma, taste and appearance of each sample rounded to the closest value. Scores regarding control and OEOF samples (without essential oil), are common with those reported in our previous study [52].

Figure 8
Figure 8

Distribution (%) of Listeria monocytogenes strains recovered from ham slices at three time points (beginning, middle, end) during storage at 4 °C based on the pulsed field gel electrophoresis (PFGE) profiles, for control samples (I), samples with edible film free from oregano essential oil—OEOF (II), samples with edible film supplemented with oregano essential oil—OEOS (III), without (a) or after (b) high pressure processing treatment.

Figure 9
Figure 9

Distribution (%) of Listeria monocytogenes strains recovered from ham slices at three time points (beginning, middle, end) during storage at 8 °C based on the pulsed field gel electrophoresis (PFGE) profiles, for control samples (I), samples with edible film free from oregano essential oil—OEOF (II), samples with edible film supplemented with oregano essential oil—OEOS (III), without (a) or after (b) high pressure processing treatment.

Figure 10
Figure 10

Distribution (%) of Listeria monocytogenes strains recovered from ham slices at three time points (beginning, middle, end) during storage at 12 °C based on the pulsed field gel electrophoresis (PFGE) profiles, for control samples (I), samples with edible film free from oregano essential oil—OEOF (II), samples with edible film supplemented with oregano essential oil—OEOS (III), without (a) or after (b) high pressure processing treatment.

Figure 11
Figure 11

Typical raw FTIR spectra in the range of 4000–650 cm−1, at the end of the shelf-life at 12 °C, without (A) or after (B) high pressure processing treatment for control samples ( – ), samples with oregano essential oil-free edible films—OEOF ( – ), and samples with edible films supplemented with oregano essential oil—OEOS ( – ).

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