PhD Vermeiren Lieve Compleet - Hogeschool Gent

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with a high glucose content of about 1.3% (w/w) glucose. The difficulty in quantifying such an interaction was to individually follow the growth of the homofermentative LAB-strain on the one hand and the growth of the heterofermentative LAB-strain on the other hand when growing in co-culture on the MCH. To resolve this issue, the medium TC8-MRS-agar, consisting of MRS-agar supplemented with tetracycline at 8 µg/ml, was developed. This agar medium allowed the differentiation of LM4-colonies from 10A-colonies or LS5-colonies after incubation for three days at 30°C under anaerobic conditions. When artificially contaminating the MCH with BT1 at 10 2 cfu/g in combination with 10A at 10 5 cfu/g, the growth of BT1 was significantly slower compared to its simultaneous monoculture growth. In a similar experiment with LM4, this strain reached a level of 10 7 cfu/g approximately 14 days later when LM4 grew together with L. sakei 10A compared to its growth in mono-culture. The lactocin S producing LS5 did not demonstrate an inhibitory action towards LM4 or BT1. On the MCH with low glucose content as well as on the MCH with high glucose content, antagonistic interactions of L. sakei 10A towards LM4 and BT1 occurred; the antagonistic effect of L. sakei 10A was not eliminated when glucose was abundant in the product. The results of this chapter indicated that L. sakei 10A has potential as protective culture for the shelf-life prolongation of CMP, while Lactobacillus sakei LS5 had not. Chapter 5 investigated the same potential protective cultures that had been studied in chapter 4, being the Lactobacillus sakei subsp. carnosus strain (10A) and the lactocin S producing Lactobacillus sakei 148 (LS5). Their capacity to increase the food safety and in particular to control the growth of L. monocytogenes on CMP was investigated. The interaction between these LAB and a cocktail of three L. monocytogenes strains was examined in co-culture studies on a MCH. Furthermore, the influence of the inoculum level (10 5 cfu/g versus 10 6 cfu/g), storage temperature (4°C versus 7°C) and packaging type (vacuum packaging versus modified atmosphere packaging) on the interaction phenomena was investigated. At 7°C, applying L. sakei 10A at 10 6 cfu/g limited the growth of L. monocytogenes to a level
10A and an atmosphere containing 50% of CO2 completely inhibited the growth of L. monocytogenes. Sensory assessment and pH-measurements confirmed that L. sakei 10A, even when present at a high level (>7 log10(cfu/g)) for prolonged storage times (up to 42 days), did not acidify the cooked ham to a point of sensory rejection. Biopreservation has been proven to be a promising natural preservation technique, but the impact of protective cultures on the sensory properties of CMP is not well documented. Chapter 6 presented a case study on the protective culture L. sakei 10A to obtain a clear view on the real consequences of using protective cultures on the sensory quality of CMP. A preliminary screening study on 13 different CMP and more elaborate application trials at 7°C on vacuum packaged pâté, cooked ham, cooked sausage and two cooked poultry products demonstrated that L. sakei 10A inhibits the growth of the endogenous LAB-flora and of artificially inoculated Leuc. mesenteroides, B. thermosphacta and L. monocytogenes cells. Despite these promising antagonistic effects, the application of L. sakei 10A to CMP was in some cases limited by a significant acidification resulting in an acid taste of the product. This was most obvious in pâté and cooked sausage and less obvious in cooked turkey fillet. The hypothesis could be derived that high buffering capacity and low glucose content are essential properties to avoid sensory deviations when applying protective cultures on CMP. The study presented in chapter 7 investigated possible mechanisms by which the nonbacteriocinogenic L. sakei 10A inhibits L. monocytogenes. First, the antagonistic character of L. sakei 10A was confirmed by the observation of growth inhibition of L. monocytogenes in the presence of 10A in buffered BHI-broth (b-BHI) (7°C, anaerobic). When assessing the growth of L. monocytogenes in the cell free supernatants (CFS), obtained after centrifugation of a 10A-culture at different time points during its growth in b-BHI, it became clear that the older the culture was, the more inhibitory properties it had, meaning that either production of (an) antimicrobial compound(s) or nutrient competition caused the inhibition. The precise role of lactic acid production and nutrient competition was more obvious during co-culture experiments in two types of broth, differing from each other in their glucose level and in the presence/absence of yeast extract, Mn 2+ and Mg 2+ . The presence of more nutrients did not prevent the growth inhibition of L. monocytogenes by L. sakei 10A. In the nutrientpoor broth, inhibition coincided with the moment of glucose depletion. In the nutrient-rich broth, an increased lactic acid production was thought to cause the inhibition. Subsequent Summary xiv
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 18 and 19: Introduction and objectives In rece
Page 20 and 21: • Sub-objective 5 Chapter 5 aimed
Page 22: Summary
Page 25: Chapter 3 presented a systematic st
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
Page 68 and 69: 3.2.2. Organic acids In general, re
Page 70 and 71: Furthermore, protective LAB can be
Page 72 and 73: Fish, fish products and seafood Spo
Page 74 and 75: Table 1.3. Effect of (non-)bacterio
Page 76 and 77:
performance as a biopreservative in
Page 78 and 79:
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
Page 221 and 222:
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
Page 240:
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
Page 274 and 275:
References 1. Aasen, I.M., Markusse
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26. Berry, E.D., Liewen, M.B., Mand
Page 278 and 279:
50. Buncic, S., Avery, S.M. & Moorh
Page 280 and 281:
75. Devlieghere, F., Debevere, J. &
Page 282 and 283:
99. Foegeding, P.M., Thomas, A.B.,
Page 284 and 285:
125. Hudson, J.A., Billington, C.,
Page 286 and 287:
150. Korkeala, H., Alanko, T., Mäk
Page 288 and 289:
174. Marceau, A., Zagorec, M. & Cha
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nonbacteriocinogenic Carnobacterium
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style green olive fermentations. Ap
Page 294 and 295:
253. Stratford, M. (2000). Traditio
Page 296:
277. Vitas, A.I. & Garcia-Jalon, V.
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Curriculum vitae Curriculum vitae L
Page 302 and 303:
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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