PhD Vermeiren Lieve Compleet - Hogeschool Gent

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1.5.1. Fermentation end-products 1.5.1.1. Organic acids Lactic acid bacteria are characterised primarily by their ability to form organic acids from the fermentation of carbohydrates. Depending on their homo- or heterofermentative nature, only lactic acid or lactic acid and other organic acids, e.g. acetic acid and propionic acid, are produced. The antimicrobial activity of these acidic end-products and the concomitant low pH constitute the most important antimicrobial system of LAB (De Vuyst & Vandamme, 1994a). The organic acids produced by LAB are weak acids and follow the common equilibrium reaction and equation HA H + + A - + − [ H ] ⋅ [ A ] a [ HA] where [H + ] is the concentration of protons, [A - ] is the concentration of anions, [HA] is the concentration of undissociated acid and Ka is the dissociation constant (Eklund, 1989). Only in their undissociated and uncharged form, organic acids are able to penetrate the microbial cell to act antimicrobially (Russell, 1992; Stratford, 2000). From the above equation it can be derived that the inhibitory activity of organic acids is determined by the pH, the dissociation constant (Ka) and the acid concentration. The antimicrobial activity of organic acids increases with decreasing pH-value since a greater proportion of undissociated molecules exists as the pH decreases. Because they are weak acids, organic acids have high pKa values (acetic acid, pKa = 4.73 and lactic acid, pKa = 3.86) (Eklund, 1989; Bogaert & Naidu, 2000). At a given pH and acid concentration, the acid with the highest pKa will have the most undissociated acid present, resulting in the strongest antimicrobial activity. This explains partly why, at a given pH, acetic acid is more inhibitory than lactic acid (Stratford, 2000). Traditionally, the antimicrobial activity of organic acids was explained by reduction of the pH below the minimum pH for growth and inhibition by undissociated acid (Russell, 1992). The mechanism of action is complex and the uncoupling theory (Russell, 1992) or weak acid theory (Stratford, 2000) has been developed (Figure 1.3). This theory states that when Chapter 1 – Antagonistic micro-organisms for biopreservation of food products 9 K =
undissociated acid molecules enter a microbial cell, at the higher intracellular pH, they dissociate in charged anions and protons, both unable to diffuse out of the cell thus reducing the intracellular pH (Eklund, 1989; Russell, 1992). A low cytoplasmic pH causes structural changes in proteins, nucleic acids and phospholipids, influences rates of enzyme action and in this way interferes with essential metabolic functions and prevents active transport requiring a ΔH + -gradient (Eklund, 1989; Stratford, 2000). To maintain or raise internal pH, a compensating transport of protons out of the cell takes place by membrane-bound H + - ATPases but consumes excessive ATP (Stratford, 2000). The remaining anion inside the cell can be driven to the outside of the cell by the electrochemical gradient. The anion is protonated again to repeat the cycle until the proton motive force is dissipated and the cell is inhibited by energy depletion (Eklund, 1989; Russell, 1992; Stratford, 2000). The last decade, however, the organic acids are regarded as having not one but several mechanisms of action and inhibition of active nutrient transport by neutralisation of the proton motive force only XCOOH XCOOH is not believed to fully explain their XCOO antimicrobial activity (Eklund, 1989; Russell, 1992). Lactic acid is acting partly according Figure 1.3. Weak acid theory and dissipation of the proton to the weak acid theory, motive force (modified from Russell, 1992 and Stratford, 2000) but other mechanisms of inhibition are also involved (Eklund, 1989; Bogaert & Naidu, 2000; Stratford, 2000). Furthermore, it has been shown that the effects of lactic acid on microbial growth at different pH can only be explained if both the undissociated and the dissociated form are taken into account (Gonçalves et al., 1997). Organic acids have a wide inhibitory spectrum including Gram-positive and Gram-negative bacteria, yeasts and moulds. Lactic acid mainly acts against bacteria and is ineffective against yeast and moulds (Eklund, 1989; Bogaert & Naidu, 2000). Lactic acid and its salts are reported to have an inhibitory effect on LAB (Houtsma et al., 1993), spore-forming Clostridia and Bacillus spp. (Bogaert & Naidu, 2000), Listeria monocytogenes (Houtsma et al., 1993) as well as on Gram-negative pathogens such as E. coli 0157:H7 and Salmonella spp. This property makes organic acids attractive food preservatives. - H + XCOO - H + ADP + Pi ATP H + Chapter 1 – Antagonistic micro-organisms for biopreservation of food products 10
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 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 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
Page 80 and 81: prevent them from growth of food bo
Page 82 and 83: The application of the host-specifi
Page 84 and 85: Multiplicity of infection (MOI) Pha
Page 86 and 87: using Leuc. carnosum 4010 in frankf
Page 88 and 89: activity of LAB in general, this se
Page 90 and 91: effect (Gram et al., 2002). Several
Page 92 and 93: for one or more of these vitamins o
Page 94 and 95: clinical cases, patients were immun
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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
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2. ILSI Europe 2nd International Sy
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13. EFSA Colloquium On Microorganis
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PhD Vermeiren Lieve Compleet - Hogeschool Gent

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