PhD Vermeiren Lieve Compleet - Hogeschool Gent

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Introduction and objectives In recent years there has been an increase in consumer concern about the use of chemical additives to ensure product safety and to extend the shelf-life of foods. In response to these concerns, efforts have been made to introduce alternative biological preservatives (Guinane et al., 2005). In view of the consumer trends towards natural and healthy food products, preservation by the use of micro-organisms and/or their metabolites has been proposed. In biopreservation the applied micro-organisms are mostly bacteria, in particular lactic acid bacteria, and they are designated as protective cultures (Holzapfel et al., 1995; Lücke, 2000). Considerable research has been done on the ability to inhibit growth of food born pathogens and in particular Listeria monocytogenes by means of protective cultures. The potential of these cultures to control growth of spoilage micro-organisms, including the endogenous lactic acid flora, has not been examined to the same extent (Leisner et al., 1996). The majority of the work in the field of biopreservation had the intention of demonstrating the effect of protective cultures being active through bacteriocin production. However, the sometimes limited effectiveness of these cultures in the meat substrate (Rodriguez et al., 2002) and the concern for resistance development (Ennahar et al., 2000) has driven the search for alternative non-bacteriocinogenic protective cultures. Furthermore, the concept of biopreservation has been well developed for applications in fermented products since it is common to use bacteria as starter cultures in these products. However, the addition of micro-organisms to nonfermented products is a rather new concept. Recently, there is also an increased interest in the use of bacteriophages, viruses that infect and kill bacteria, as a means of inactivating food born pathogens (Hudson et al., 2005). The primary objective of this work was to investigate the possibility of preserving sliced, cooked meat products (CMP), which are packaged either under vacuum or under a modified atmosphere, by means of non-bacteriocinogenic micro-organisms and to study the mechanism of action behind this non-bacteriocinogenic type of biopreservation. The main part (Chapters 2 to 7) of this work studied biopreservation by means of nonbacteriocinogenic lactic acid bacteria and this using an integrated approach since all different aspects concerning this preservation technology were investigated: effectiveness, sensory aspects and mechanism of inhibition. To realise the stipulated objectives, one particular protective LAB-culture had to be selected during the research to use this culture as a case Introduction and objectives vii
study. The results from the case-study could then be used to derive general conclusions on this biopreservation technology. In the final chapter (Chapter 8) of this <strong>PhD</strong>-work, preservation of cooked meat products by means of bacteriophages was introduced as an additional subject of research. The outline of this work is schematically presented in Figure 0.1. The following subobjectives of this work can be stipulated: • Sub-objective 1 Before starting this <strong>PhD</strong>-work, it was of primary importance to study the existing knowledge in literature concerning antagonistic micro-organisms for biopreservation of food products (Chapter 1). • Sub-objective 2 In chapter 2, collected and isolated meat born lactic acid bacteria were tested for their suitability to be candidate protective cultures for cooked meat products. Besides testing whether the cultures had a ‘protective’ activity, they also needed to be adapted to the product/storage conditions (psychrotrophic character, salt tolerance). Furthermore, it was of primary concern to evaluate, already at this early stage of the work, the effect of the cultures on the sensory properties of a model cooked meat product. • Sub-objective 3 Chapter 3 aimed to better understand spoilage caused by different types of spoilage organisms, associated with vacuum packaged sliced CMP. The systematic study on the behaviour of several spoilage organisms on a model product, imitating cooked ham, was meant to establish the relationship between microbial growth, pH-evolution, metabolite formation and the occurrence of organoleptic deviations. • Sub-objective 4 Chapter 4 had the objective to examine the interaction between the candidate protective cultures, that had been selected in chapter 2, and the spoilage organisms, that were shown to be most relevant for anaerobically packaged sliced CMP in chapter 3. Chapter 4 aimed to answer the question: can homofermentative non-bacteriocinogenic lactic acid bacteria be used to prolong the shelf-life of CMP? Introduction and objectives viii
Page 1: Hogeschool Gent Biopreservation of
Page 4 and 5: ir. Lieve Vermeiren Biopreservation
Page 6 and 7: Woord vooraf Proefbuizen, labojasse
Page 8: Table of contents
Page 11 and 12: 3.4. EFFECT OF PROTECTIVE LAB ON TH
Page 13 and 14: 1. INTRODUCTION....................
Page 15 and 16: 2.8. STATISTICAL ANALYSES 189 3. RE
Page 20 and 21: • Sub-objective 5 Chapter 5 aimed
Page 22: Summary
Page 25 and 26: Chapter 3 presented a systematic st
Page 27 and 28: 10A and an atmosphere containing 50
Page 30: Samenvatting
Page 33 and 34: werden deze stammen beschouwd als m
Page 35 and 36: ewaartemperatuur (4°C versus 7°C)
Page 37 and 38: In-vitro testen toonden aan dat de
Page 40 and 41: Chapter 1 Antagonistic micro-organi
Page 42 and 43: esides lactic acid, including carbo
Page 44 and 45: 1.4.3. The genus Pediococcus This g
Page 46 and 47: taxonomy) and the present phylogene
Page 48 and 49: 1.5.1. Fermentation end-products 1.
Page 50 and 51: The ability of lactic acid to rotat
Page 52 and 53: 1.5.2. Bacteriocins Bacteriocins, p
Page 54 and 55: molecule inserts into the membrane
Page 56 and 57: 1.5.3. Other antagonistic systems 1
Page 58 and 59: explains why CMP, immediately after
Page 60 and 61: Weissella Weissella viridiscens has
Page 62 and 63: 2.3.3.3. Discolouration Green disco
Page 64 and 65: eported an incidence of L. monocyto
Page 66 and 67: The use of micro-organisms or their
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3.2.2. Organic acids In general, re
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Furthermore, protective LAB can be
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Fish, fish products and seafood Spo
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Table 1.3. Effect of (non-)bacterio
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performance as a biopreservative in
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Table 1.6. Studies on the effect of
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prevent them from growth of food bo
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The application of the host-specifi
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Multiplicity of infection (MOI) Pha
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using Leuc. carnosum 4010 in frankf
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activity of LAB in general, this se
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effect (Gram et al., 2002). Several
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for one or more of these vitamins o
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clinical cases, patients were immun
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different degrees and classify them
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this way an equal distribution over
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Chapter 2 Evaluation of meat born l
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temperatures, the characterisation
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dextranicum LMG 6908 T , Leuc. carn
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2.6. Behaviour of 12 selected putat
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considered as unacceptable. Finally
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From the 74 remaining strains, only
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Among the isolates, 76% (28/37) was
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Within the group of isolated strain
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with fast growth rates at low tempe
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pH 6.3 6.2 6.1 6.0 5.9 5.8 5.7 0 5
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34th day of the storage period, alt
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Table 2.5. Summary of the LAB-count
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Chapter 3 In-vitro and in-situ grow
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1. Introduction A considerable part
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7°C and revived by transferring a
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The sensory quality of cooked ham s
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lesser extent compared to the LAB s
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LC2 and LM3 not significantly decre
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Sensory rejection was mainly based
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log10(cfu/g), respectively. It migh
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Chapter 4 Co-culture experiments de
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1. Introduction Interest in the rol
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growth characteristics, antibacteri
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1 g/l Peptone (Oxoid)) was prepared
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were sensitive to 8/11 tested antib
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Log10(cfu/g) Log10(cfu/g) 9 8 7 6 5
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On the other hand, no significant (
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Table 4.3. Evolution of the glucose
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Log10(cfu/g) Log10(cfu/g) 9 8 7 6 5
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day 28 in the HG-product. However,
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glucose. Buchanan & Bagi (1997) als
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Chapter 5 The interaction of the no
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1. Introduction Several authors hav
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(3) an interaction study at 7°C be
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3. Results and discussion The chemi
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Log10(cfu/g) 9 8 7 6 5 4 3 2 1 0 0
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Clearly, the growth of L. sakei 10A
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Table 5.2. Evolution of the pH of t
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Chapter 6 The sensory acceptability
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1. Introduction During the last dec
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mixture of Leuc. mesenteroides LM2
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to a sensory panel of 18 non-traine
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inoculation, 200 g portions of prod
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Buffering capacity (mmol lactic aci
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where LAB-growth results in sensory
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3.2.1. Antagonistic activity of L.
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In all five products, L. sakei 10A
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the glucose consumption in 10A-samp
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In general, CMP with such low pH-va
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3.3. Discussion 3.3.1. Antagonistic
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that cooked ring sausages were deem
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Chapter 7 The contribution of lacti
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1. Introduction The last two decade
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Table 7.1. Composition of the diffe
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In all three experiments, growth of
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2.5.2. Challenge experiment in CFS
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3. Results and discussion 3.1. Co-c
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However, cell numbers were analysed
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Log10(cfu/ml) or pH Log10(cfu/ml) o
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Log10(cfu/ml) Log10(cfu/ml) 10 9 8
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Log10(cfu/ml) Log10(cfu/ml) 9 8 7 6
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that case the pH of the CFS would h
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Log10(cfu/ml) Log10(cfu/ml) 9 8 7 6
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these experiments when there was st
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Chapter 8 Treatment with bacterioph
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1. Introduction Listeria monocytoge
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(7°C and 30°C). Experiments were
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L. monocytogenes cocktail, 100 µl
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3. Results and discussion 3.1. Effe
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susceptibility of the genus Listeri
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end-point for the microbial shelf-l
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therefore, be sufficient to control
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contaminated cooked meat products,
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General discussion, conclusions and
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possible that the bacteriocin was n
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manufactured cooked meat products (
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deviations can be prevented and led
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List of abbreviations
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pfu plaque forming unit PPS Pepton
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References 1. Aasen, I.M., Markusse
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26. Berry, E.D., Liewen, M.B., Mand
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50. Buncic, S., Avery, S.M. & Moorh
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75. Devlieghere, F., Debevere, J. &
Page 282 and 283:
99. Foegeding, P.M., Thomas, A.B.,
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125. Hudson, J.A., Billington, C.,
Page 286 and 287:
150. Korkeala, H., Alanko, T., Mäk
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174. Marceau, A., Zagorec, M. & Cha
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nonbacteriocinogenic Carnobacterium
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style green olive fermentations. Ap
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253. Stratford, M. (2000). Traditio
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277. Vitas, A.I. & Garcia-Jalon, V.
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Curriculum vitae Curriculum vitae L
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of Listeria monocytogenes by the no
Page 304 and 305:
2. ILSI Europe 2nd International Sy
Page 306:
13. EFSA Colloquium On Microorganis
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PhD Vermeiren Lieve Compleet - Hogeschool Gent

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