1
|
Bendig T, Ulmer A, Luzia L, Müller S, Sahle S, Bergmann FT, Lösch M, Erdemann F, Zeidan AA, Mendoza SN, Teusink B, Takors R, Kummer U, Figueiredo AS. The pH-dependent lactose metabolism of Lactobacillus delbrueckii subsp. bulgaricus: An integrative view through a mechanistic computational model. J Biotechnol 2023; 374:90-100. [PMID: 37572793 DOI: 10.1016/j.jbiotec.2023.08.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Revised: 07/20/2023] [Accepted: 08/07/2023] [Indexed: 08/14/2023]
Abstract
The fermentation process of milk to yoghurt using Lactobacillus delbrueckii subsp. bulgaricus in co-culture with Streptococcus thermophilus is hallmarked by the breakdown of lactose to organic acids such as lactate. This leads to a substantial decrease in pH - both in the medium, as well as cytosolic. The latter impairs metabolic activities due to the pH-dependence of enzymes, which compromises microbial growth. To quantitatively elucidate the impact of the acidification on metabolism of L. bulgaricus in an integrated way, we have developed a proton-dependent computational model of lactose metabolism and casein degradation based on experimental data. The model accounts for the influence of pH on enzyme activities as well as cellular growth and proliferation of the bacterial population. We used a machine learning approach to quantify the cell volume throughout fermentation. Simulation results show a decrease in metabolic flux with acidification of the cytosol. Additionally, the validated model predicts a similar metabolic behaviour within a wide range of non-limiting substrate concentrations. This computational model provides a deeper understanding of the intricate relationships between metabolic activity and acidification and paves the way for further optimization of yoghurt production under industrial settings.
Collapse
Affiliation(s)
- Tamara Bendig
- BioQuant, Centre for Organismal Studies (COS), Heidelberg University, Heidelberg, Germany
| | - Andreas Ulmer
- Institute of Biochemical Engineering, University of Stuttgart, Stuttgart, Germany
| | - Laura Luzia
- Systems Biology Lab, Vrije Universiteit, Amsterdam, the Netherlands
| | - Susanne Müller
- Institute of Biochemical Engineering, University of Stuttgart, Stuttgart, Germany
| | - Sven Sahle
- BioQuant, Centre for Organismal Studies (COS), Heidelberg University, Heidelberg, Germany
| | - Frank T Bergmann
- BioQuant, Centre for Organismal Studies (COS), Heidelberg University, Heidelberg, Germany
| | - Maren Lösch
- Institute of Biochemical Engineering, University of Stuttgart, Stuttgart, Germany
| | - Florian Erdemann
- Institute of Biochemical Engineering, University of Stuttgart, Stuttgart, Germany
| | - Ahmad A Zeidan
- Systems Biology, R&D Discovery, Chr. Hansen A/S, Hørsholm, Denmark
| | | | - Bas Teusink
- Systems Biology Lab, Vrije Universiteit, Amsterdam, the Netherlands
| | - Ralf Takors
- Institute of Biochemical Engineering, University of Stuttgart, Stuttgart, Germany
| | - Ursula Kummer
- BioQuant, Centre for Organismal Studies (COS), Heidelberg University, Heidelberg, Germany.
| | - Ana Sofia Figueiredo
- BioQuant, Centre for Organismal Studies (COS), Heidelberg University, Heidelberg, Germany.
| |
Collapse
|
2
|
Bouix M, Ghorbal S, Picque D, Perret B, Saulou-Berion C. A rapid method for the assessment of the vitality of microorganisms using flow cytometry. Cytometry A 2022; 101:577-587. [PMID: 35324070 DOI: 10.1002/cyto.a.24553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Revised: 02/25/2022] [Accepted: 03/15/2022] [Indexed: 11/06/2022]
Abstract
Cultivability, viability and vitality make it possible to characterize the behavior of a cellular population. Vitality was assessed using the kinetic parameters of specific metabolisms depending on whether the strains were used, for example, for the acidification of lactic acid bacteria or for CO2 production in fermenting yeasts. However, these methods are time-consuming. We developed a cytometric descriptor based on the energy-dependent extrusion of carboxyfluorescein from cells, subsequent to carboxyfluorescein diacetate staining, and compared it to the measurements of metabolic activities of various bacteria and yeasts. For all of the microorganisms tested, the cytometric descriptor ΔFI15 was well correlated with the results of the metabolic measurements and, moreover, has the advantage of being easier and faster to use than metabolic methods. It can be very useful for evaluating the vitality of the starters before inoculation in industrial processes. This article is protected by copyright. All rights reserved.
Collapse
Affiliation(s)
- Marielle Bouix
- Université Paris-Saclay, AgroParisTech, INRAe, UMR SayFood, Thiverval-Grignon, France
| | - Sarrah Ghorbal
- Université Paris-Saclay, AgroParisTech, INRAe, UMR SayFood, Thiverval-Grignon, France
| | - Daniel Picque
- Université Paris-Saclay, AgroParisTech, INRAe, UMR SayFood, Thiverval-Grignon, France
| | - Bruno Perret
- Université Paris-Saclay, AgroParisTech, INRAe, UMR SayFood, Thiverval-Grignon, France
| | - Claire Saulou-Berion
- Université Paris-Saclay, AgroParisTech, INRAe, UMR SayFood, Thiverval-Grignon, France
| |
Collapse
|
3
|
Chen S, Gong P, Zhang J, Shan Y, Han X, Zhang L. Use of qPCR for the analysis of population heterogeneity and dynamics during Lactobacillus delbrueckii spp. bulgaricus batch fculture. ARTIFICIAL CELLS NANOMEDICINE AND BIOTECHNOLOGY 2021; 49:1-10. [PMID: 33356615 DOI: 10.1080/21691401.2020.1860074] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Direct molecular methods such as real-time polymerase chain reaction (qPCR) and propidium monoazide (PMA)-qPCR have been successfully used for quantifying viable microorganisms in the food industry. This study attempted to use qPCR and PMA-qPCR for quantifying Lactobacillus delbrueckii spp. bulgaricus sp1.1 physiological states. The qPCR standards of the 16S rRNA gene were employed to calibrate the qPCR assay, which contributed to an amplification efficiency of 98.42%. The number of copies of the 16S rRNA gene was linearly related to cell density, and this linear relationship was used to construct a quantitative curve (R2 =0.9981) with a detection limit of 15.1 colony-forming units mL-1·reaction-1. qPCR in combination with an optimal PMA concentration (60 μM) helped in discriminating and quantifying the viable cells, without any interference by heat-killed cells. Compared with the conventional methods, the population heterogeneity of viable, culturable, dormant-like and membrane-permeabilized cells were well identified and quantified using qPCR during L. delbrueckii spp. bulgaricus sp1.1 batch culture. Despite the restriction in the enumeration of lysed cells, qPCR-based methods facilitated reliable identification and quantification of bacterial physiological states and provided additional knowledge on the dynamics of L. delbrueckii spp. bulgaricus sp1.1 physiological states.
Collapse
Affiliation(s)
- Shiwei Chen
- School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, China
| | - Pimin Gong
- School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, China
| | - Jianming Zhang
- School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, China
| | - Yujuan Shan
- School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, China
| | - Xue Han
- School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, China
| | - Lanwei Zhang
- School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, China.,College of Food Science and Engineering, Ocean University of China, Qingdao, China
| |
Collapse
|
4
|
Imbalance between peptidoglycan synthases and hydrolases regulated lysis of Lactobacillus bulgaricus in batch culture. Arch Microbiol 2021; 203:4571-4578. [PMID: 34156502 DOI: 10.1007/s00203-021-02433-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 06/05/2021] [Accepted: 06/09/2021] [Indexed: 12/23/2022]
Abstract
Lactobacillus bulgaricus is an important starter culture in the dairy industry, cell lysis is negative to the high density of this strain. This work describes the response of peptidoglycan synthases and hydrolases in Lactobacillus bulgaricus sp1.1 when pH decreasing in batch culture. First, the cell lysis was investigated by measuring the cytosolic lactate dehydrogenase released to the fermentation broth, a continuous increase in extracellular lactate dehydrogenase was observed after the lag phase in batch culture. Then, the peptidoglycan hydrolases profile analyzed using the zymogram method showed that eight proteins have the ability of peptidoglycan hydrolysis, three of the eight proteins were considered to contribute lysis of L. bulgaricus sp1.1 according to the changes and extents of peptidoglycan hydrolysis. In silico analysis showed that three putative peptidoglycan hydrolases, including N-acetylmuramyl-L-Ala amidase (protein ID: ALT46642.1), amidase (protein ID: ALT46641.1), and N-acetylmuramidase (protein ID: WP_013439201.1) were compatible with these proteins. Finally, the transcription of the three putative peptidoglycan hydrolases was upregulated in batch culture, in contrast, the expression of four peptidoglycan synthases was downregulated. These observations suggested the imbalance between peptidoglycan synthases and hydrolases involved in the lysis of Lactobacillus bulgaricus sp1.1.
Collapse
|
5
|
Chen S, Gong P, Zhang J, Shan Y, Han X, Zhang L. Quantitative analysis of Lactobacillus delbrueckii subsp. bulgaricus cell division and death using fluorescent dye tracking. J Microbiol Methods 2020; 169:105832. [DOI: 10.1016/j.mimet.2020.105832] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2019] [Revised: 12/29/2019] [Accepted: 01/01/2020] [Indexed: 12/30/2022]
|
6
|
Buysschaert B, Byloos B, Leys N, Van Houdt R, Boon N. Reevaluating multicolor flow cytometry to assess microbial viability. Appl Microbiol Biotechnol 2016; 100:9037-9051. [PMID: 27687990 DOI: 10.1007/s00253-016-7837-5] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Revised: 08/29/2016] [Accepted: 09/01/2016] [Indexed: 01/14/2023]
Abstract
Flow cytometry is a rapid and quantitative method to determine bacterial viability. Although different stains can be used to establish viability, staining protocols are inconsistent and lack a general optimization approach. Very few "true" multicolor protocols, where dyes are combined in one sample, have been developed for microbiological applications. In this mini-review, the discrepancy between protocols for cell-permeant nucleic acid and functional stains are discussed as well as their use as viability dyes. Furthermore, optimization of staining protocols for a specific setup are described. Original data using the red-excitable SYTO dyes SYTO 59 to 64 and SYTO 17, combined with functional stains, for double and triple staining applications is also included. As each dye and dye combination behaves differently within a certain combination of medium matrix, microorganism, and instrument, protocols need to be tuned to obtain reproducible results. Therefore, single, double, and triple stains are reviewed, including the different parameters that influence staining such as stain kinetics, optimal stain concentration, and the effect of the chelator EDTA as membrane permeabilizer. In the last section, we highlight the need to investigate the stability of multicolor assays to ensure correct results as multiwell autoloaders are now commonly used.
Collapse
Affiliation(s)
- Benjamin Buysschaert
- Centre for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, 9000, Ghent, Belgium
| | - Bo Byloos
- Centre for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, 9000, Ghent, Belgium.,Unit of Microbiology, Belgian Nuclear Research Centre (SCK-CEN), Boeretang 200, 2400, Mol, Belgium
| | - Natalie Leys
- Unit of Microbiology, Belgian Nuclear Research Centre (SCK-CEN), Boeretang 200, 2400, Mol, Belgium
| | - Rob Van Houdt
- Unit of Microbiology, Belgian Nuclear Research Centre (SCK-CEN), Boeretang 200, 2400, Mol, Belgium
| | - Nico Boon
- Centre for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, 9000, Ghent, Belgium.
| |
Collapse
|
7
|
Hansen G, Johansen CL, Marten G, Wilmes J, Jespersen L, Arneborg N. Influence of extracellular pH on growth, viability, cell size, acidification activity, and intracellular pH of Lactococcus lactis in batch fermentations. Appl Microbiol Biotechnol 2016; 100:5965-76. [DOI: 10.1007/s00253-016-7454-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Revised: 03/06/2016] [Accepted: 03/09/2016] [Indexed: 11/27/2022]
|
8
|
Alonso S. Novel Preservation Techniques for Microbial Cultures. NOVEL FOOD FERMENTATION TECHNOLOGIES 2016. [DOI: 10.1007/978-3-319-42457-6_2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
|
9
|
Bouix M, Ghorbal S. Rapid assessment of Oenococcus oeni activity by measuring intracellular pH and membrane potential by flow cytometry, and its application to the more effective control of malolactic fermentation. Int J Food Microbiol 2015; 193:139-46. [DOI: 10.1016/j.ijfoodmicro.2014.10.019] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2014] [Revised: 10/03/2014] [Accepted: 10/17/2014] [Indexed: 11/28/2022]
|
10
|
Velly H, Fonseca F, Passot S, Delacroix-Buchet A, Bouix M. Cell growth and resistance of Lactococcus lactis
subsp. lactis
TOMSC161 following freezing, drying and freeze-dried storage are differentially affected by fermentation conditions. J Appl Microbiol 2014; 117:729-40. [DOI: 10.1111/jam.12577] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2014] [Revised: 05/31/2014] [Accepted: 06/12/2014] [Indexed: 11/30/2022]
Affiliation(s)
- H. Velly
- CNIEL; Paris Cedex 09 France
- INRA; UMR 782 Génie et Microbiologie des Procédés Alimentaires (GMPA); Thiverval-Grignon France
- AgroParisTech; UMR 782 Génie et Microbiologie des Procédés Alimentaires (GMPA); Thiverval-Grignon France
| | - F. Fonseca
- INRA; UMR 782 Génie et Microbiologie des Procédés Alimentaires (GMPA); Thiverval-Grignon France
- AgroParisTech; UMR 782 Génie et Microbiologie des Procédés Alimentaires (GMPA); Thiverval-Grignon France
| | - S. Passot
- INRA; UMR 782 Génie et Microbiologie des Procédés Alimentaires (GMPA); Thiverval-Grignon France
- AgroParisTech; UMR 782 Génie et Microbiologie des Procédés Alimentaires (GMPA); Thiverval-Grignon France
| | - A. Delacroix-Buchet
- INRA; UMR 1319 Microbiologie de l'alimentation au service de la santé (Micalis); Jouy-en-Josas France
- AgroParisTech; UMR 1319 Microbiologie de l'alimentation au service de la santé (Micalis); Jouy-en-Josas France
| | - M. Bouix
- INRA; UMR 782 Génie et Microbiologie des Procédés Alimentaires (GMPA); Thiverval-Grignon France
- AgroParisTech; UMR 782 Génie et Microbiologie des Procédés Alimentaires (GMPA); Thiverval-Grignon France
| |
Collapse
|
11
|
El Arbi A, Ghorbal S, Delacroix-Buchet A, Bouix M. Assessment of the dynamics of the physiological states of Lactococcus lactis ssp. cremoris SK11 during growth by flow cytometry. J Appl Microbiol 2011; 111:1205-11. [PMID: 21787374 DOI: 10.1111/j.1365-2672.2011.05114.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
AIMS The aim of this study was to improve knowledge about the dynamics of the physiological states of Lactococcus lactis ssp. cremoris SK11, a chain-forming bacterium, during growth, and to evaluate whether flow cytometry (FCM) combined with fluorescent probes can assess these different physiological states. METHODS AND RESULTS Cellular viability was assessed using double labelling with carboxyfluorescein diacetate and propidium iodide. FCM makes it possible to discriminate between three cell populations: viable cells, dead cells and cells in an intermediate physiological state. During exponential and stationary phases, the cells in the intermediate physiological state were culturable, whereas this population was no longer culturable at the end of the stationary phase. CONCLUSIONS, AND IMPACT OF THE STUDY We introduced a new parameter, the ratio of the means of the fluorescence cytometric index to discriminate between viable culturable and viable nonculturable cells. Finally, this work confirms the relevance of FCM combined with two fluorescent stains to evaluate the physiological states of L. lactis SK11 cells during their growth and to distinguish viable cells from viable but not culturable cells.
Collapse
Affiliation(s)
- A El Arbi
- AgroParisTech, INRA, UMR 782 Génie et Microbiologie des Procédés Alimentaires, Thiverval-Grignon, France
| | | | | | | |
Collapse
|
12
|
Roger P, Delettre J, Bouix M, Béal C. Characterization of Streptococcus salivarius growth and maintenance in artificial saliva. J Appl Microbiol 2011; 111:631-41. [PMID: 21672100 DOI: 10.1111/j.1365-2672.2011.05077.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
AIMS To help gain a better understanding of factors influencing the establishment within the oral cavity of Streptococcus salivarius K12, a commensal oral bacterium, we characterized its behaviour in artificial saliva. METHODS AND RESULTS Streptococcus salivarius K12 was grown in artificial saliva complemented with a representative meal, under oral pH and temperature conditions. Exponential growth phase was characterized by a high specific growth rate (2.8 h(-1)). During maintenance phase, an uncoupling between growth and lactic acid production occurred, which allowed maintaining viability (95%), intracellular pH (6.6) and membrane polarisation (95%), and thus proton motive force. However, in late stationary phase, viability (64%) and vitality were degraded as a result of lower synthesis of energetic and glycogen-related proteins as compared to a richer medium. CONCLUSIONS Streptococcus salivarius was able to rapidly grow in complemented artificial saliva. Nevertheless, a degradation of its physiological state was observed in late-stationary phase. SIGNIFICANCE AND IMPACT OF THE STUDY This work demonstrates, for the first time, that artificial saliva was a convenient medium that permitted Strep. salivarius to grow in oral conditions (physico-chemical environment, addition of meals) but not to maintain cellular viability and vitality in starvation conditions.
Collapse
Affiliation(s)
- P Roger
- AgroParisTech, INRA, UMR782, Thiverval-Grignon, France
| | | | | | | |
Collapse
|
13
|
Rault A, Bouix M, Béal C. Cryotolerance of Lactobacillus delbrueckii subsp. bulgaricus CFL1 is influenced by the physiological state during fermentation. Int Dairy J 2010. [DOI: 10.1016/j.idairyj.2010.05.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
|
14
|
Sträuber H, Müller S. Viability states of bacteria-Specific mechanisms of selected probes. Cytometry A 2010; 77:623-34. [DOI: 10.1002/cyto.a.20920] [Citation(s) in RCA: 133] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
15
|
Díaz M, Herrero M, García LA, Quirós C. Application of flow cytometry to industrial microbial bioprocesses. Biochem Eng J 2010. [DOI: 10.1016/j.bej.2009.07.013] [Citation(s) in RCA: 132] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
|
16
|
Metabolic impact and potential exploitation of the stress reactions in lactobacilli. Food Microbiol 2009; 26:700-11. [PMID: 19747603 DOI: 10.1016/j.fm.2009.07.007] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2009] [Revised: 07/09/2009] [Accepted: 07/13/2009] [Indexed: 01/03/2023]
Abstract
Lactic acid bacteria (LAB) are a functionally related group of organisms known primarily for their bioprocessing roles in food and beverages. The largest variety of metabolic properties is found in the group of lactobacilli the vast majority of which has been isolated in cereal environments, namely sourdoughs, in which their role ranges from sporadic contaminants to major fermentative flora. Growth or survival in each of these environmental niches depends on the ability of the organism to sense and respond to varying conditions such as temperature, pH, nutrients availability and cell population density. Fermentation process conditions, including temperature range, dough yield, oxygen, pH as well as the amount and composition of starter cultures, determine the cells' metabolic response. In fact, the exposure of microbial cells to stressful conditions during fermentation involves a broad transcriptional response with many induced or repressed genes. The complex network of such responses, involving several metabolic activities will reflect upon the metabolome of the fermentative flora, and thus on the composition and organoleptic properties of the final products. This review shall provide insight into stress response mechanisms and delineate the vast potential residing in the exploitation of the stress dependent metabolome of LAB focusing on bacteria of the sourdough environment as one of the richest sources of lactobacilli.
Collapse
|
17
|
Fermentation pH influences the physiological-state dynamics of Lactobacillus bulgaricus CFL1 during pH-controlled culture. Appl Environ Microbiol 2009; 75:4374-81. [PMID: 19429565 DOI: 10.1128/aem.02725-08] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
This study aims at better understanding the effects of fermentation pH and harvesting time on Lactobacillus bulgaricus CFL1 cellular state in order to improve knowledge of the dynamics of the physiological state and to better manage starter production. The Cinac system and multiparametric flow cytometry were used to characterize and compare the progress of the physiological events that occurred during pH 6 and pH 5 controlled cultures. Acidification activity, membrane damage, enzymatic activity, cellular depolarization, intracellular pH, and pH gradient were determined and compared during growing conditions. Strong differences in the time course of viability, membrane integrity, and acidification activity were displayed between pH 6 and pH 5 cultures. As a main result, the pH 5 control during fermentation allowed the cells to maintain a more robust physiological state, with high viability and stable acidification activity throughout growth, in opposition to a viability decrease and fluctuation of activity at pH 6. This result was mainly explained by differences in lactate concentration in the culture medium and in pH gradient value. The elevated content of the ionic lactate form at high pH values damaged membrane integrity that led to a viability decrease. In contrast, the high pH gradient observed throughout pH 5 cultures was associated with an increased energetic level that helped the cells maintain their physiological state. Such results may benefit industrial starter producers and fermented-product manufacturers by allowing them to better control the quality of their starters, before freezing or before using them for food fermentation.
Collapse
|