Topic- In-vitro study on bacterial inhibition by essential oils of chicken-borne bacteria
Research Question- To what extent can the in-vitro bioactivity of the essential oils of
oregano (Origanum vulgare), thyme (Thymus vulgaris), clove (Syzygium aromaticum),
coriander seed (Coriandrum sativum) and rosemary (Rosmarinus officinalis) inhibit growth
of bacterial strains found in raw chicken breast?
Biology
May 2018
Word Count: 3992
Personal Code: glq523
Contents Page
,1.0 Introduction......................................................................................................................................... 2
1.1 Research Rationale..................................................................................................................................... 3
1.2 The Nature and Origins of Essential Oils.............................................................................................. 4
1.3 Chemical Components and Biological Activity of Essential Oils....................................................4
1.4 Chicken-borne bacteria and Interaction with Essential Oils.........................................................7
2.0 Hypotheses........................................................................................................................................... 8
3.0 Variables............................................................................................................................................... 9
4.0 Materials and Method..................................................................................................................... 10
4.1 Materials...................................................................................................................................................... 10
4.2 Method......................................................................................................................................................... 12
5.0 Data Collection.................................................................................................................................. 15
6.0 Data Processing................................................................................................................................ 17
7.0 Data Analysis..................................................................................................................................... 18
7.1 Analysis of Variation (ANOVA) Test.................................................................................................... 18
7.2 Tukey’s Post-Hoc Test.............................................................................................................................. 19
8.0 Discussion.......................................................................................................................................... 20
8.1 Essential Oil bacterial inhibition in comparison with water.......................................................20
8.2 Comparison between Essential Oils.................................................................................................... 21
9.0 Evaluation.......................................................................................................................................... 24
10.0 Conclusion....................................................................................................................................... 26
11.0 Bibliography................................................................................................................................... 26
12.0 Appendices...................................................................................................................................... 29
1.0 Introduction
2
,1.1 Research Rationale
Increasing the shelf-life of meat products such as chicken is a constant challenge for the
food industry; the food matrix of meat provides the preferential environment for bacterial
colonisation, and therefore spoilage due to bacterial decomposition occurs rapidly. This
bacterial contamination also poses a risk to human health. Pathogenic strains can be
ingested, as well as antibiotic-resistant strains that propagate due to over usage of
antibiotics for growth promotion in the livestock industry. Meat also decomposes through
lipid oxidation, whereby oxygen free radicals react with fatty acids in the meat, producing
lipid peroxides that are responsible for the undesirable odours and tastes that characterise
spoilage.1 This process can be accelerated by the release of lipase enzyme by bacteria. In
order to maximise shelf-life and minimise health risk therefore, bacterial contamination
must be restricted.
Many current methods to increase shelf-life of chicken slow the growth of bacteria rather
than directly target it. Salting is effective in producing an unfavourable water activity for
bacteria, however an increasingly negative public perception towards added salt and
sugar, combined with research revealing the dangers of synthetic meat preservatives, has
led to a need for new, plant-based preservatives 2. Essential oils (EOs) possess
antibacterial properties, and current research has shown promising results for their use as
meat additives. For example, an edible film consisting of chitosan incorporated with thyme
EO has been formulated for ready-to-eat meat, 3 showing a decrease in bacterial growth
while producing positive organoleptic effects. Furthermore, if EOs can be shown to
effectively kill bacteria in meat, there will be less of a need for excessive antibiotic usage in
livestock, decreasing the rising prevalence of antibiotic-resistant strains that are
transferred to humans via ingestion.
Hence, this research aims to investigate to what extent the EOs of thyme, rosemary,
oregano, clove and coriander seed can inhibit bacterial growth in raw chicken breast in
1
Cheng JH (2016) 'Lipid Oxidation in Meat', Journal of Nutrition and Food Sciences, 6(3), pp. 494
[Online]. Available at: https://www.omicsonline.org/open-access/lipid-oxidation-in-meat-2155-9600-
1000494.pdf
2
Don L. Zink (1997) 'The Impact of Consumer Demands and Trends on Food
Processing', Emerging Infectious Diseases, 3(4), pp. 467-468 [Online]. Available
at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2640073/pdf/9366598.pdf
3
Jesús Quesada, Esther Sendra, Casilda Navarro, and Estrella Sayas-Barberá (2016)
'Antimicrobial Active Packaging including Chitosan Films with Thymus vulgaris L. Essential Oil for
Ready-to-Eat Meat', Foods, 5(3), pp. 57 [Online]. Available
at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5302392/
3
, comparison with water. A microbiological analysis of raw chicken breast after treatment
with these EOs will be carried out using the spread plate method, and bacterial
contamination will be compared to assess which EO is most effective against the
microbiome of raw chicken.
1.2 The Nature and Origins of Essential Oils
EOs are volatile, aromatic secondary metabolites of plants. They are not synthesized with
relation to the primary functions of growth and reproduction, instead serving as a form of
chemical communication between plant and the environment for either a defence or
attraction function, for example attracting pollinators for seed dispersion, or protecting
against herbivores.4 As EO production plays an important role in the ability of a plant to
adapt to a changing environment, in evolutionary terms it would be expected that EOs
synthesised to deter bacterial contamination would be the most inhibitive.
Within a plant, EOs can originate from various sources yet are often more concentrated in
one area. EOs are commonly synthesised in the organs of the plant, including the stem,
roots and leaves; EOs from separate origins may have different chemical compositions.
EOs form as globules within specialised plant cells, secretory cavities or glandular hairs,
and can be excreted into the environment via the cells lining intercellular spaces called
schizogenous ducts.
1.3 Chemical Components and Biological Activity of Essential Oils
The following five EOs have been chosen as they are commonly used as spices in cuisine,
and if EOs are to have potential within the food industry they must possess favourable
organoleptic properties. Although the chemical makeup of each EO can vary with
differences in environment, season, extraction method and quality of extraction apparatus,
their antibacterial activity is usually attributed to only the main components, which are
outlined below.
1.3.1 Oregano (Origanum vulgare)
Oregano EO is rich in monoterpenes and sesquiterpenes: hydrocarbons that do not have
direct antibacterial effects but are thought to enhance the bioactivity of other components.
4
Cláudia L. PrinsI, Ivo J. C. VieiraII, Silvério P. FreitasI (2010) 'Growth regulators and essential oil
production', Brazilian Journal of Plant Physiology, 22(2) [Online]. Available
at: http://dx.doi.org/10.1590/S1677-04202010000200003
4
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