Secundilactobacillus collinoides within the cider microbiome: understanding and preventing the appearance of acrolein in cider products
16 May 2024
Job Information
- Organisation/Company
Université de Caen Normandie- Research Field
Biological sciences- Researcher Profile
First Stage Researcher (R1)- Country
France- Application Deadline
14 Jun 2024 - 17:00 (Europe/Paris)- Type of Contract
Temporary- Job Status
Full-time- Hours Per Week
35- Offer Starting Date
2 Sep 2024- Is the job funded through the EU Research Framework Programme?
Not funded by an EU programme- Is the Job related to staff position within a Research Infrastructure?
No
Offer Description
As part of the laboratory's research work, we are particularly interested in the place of lactic acid bacteria in these microbiomes. Indeed, this abundant and diverse flora is responsible for malolactic fermentation which makes it possible to soften ciders by lowering the pH by converting malic acid into lactic acid. But this lactic flora can also metabolize residual carbon sources, whether fructose, glycerol or lactic acid, and thus be the cause of alterations including the acroleic bite which remains the one of the main concerns of the cider industry. In fact, previous studies carried out by the Chamber of Agriculture have shown that more than 90% of producers are affected by acrolein problems (Esters and typicality program). Faced with this problem, calvados producers have adapted, choosing to distill their product at the least handicapping stage, that is to say when the precursor of acrolein, present in distillation ciders, has transformed into allyl alcohol. Thanks to this practice, the impact of acrolein in calvados brandies is relatively limited, however postponing distillation to allow the acrolein precursor to be converted into allyl alcohol has two disadvantages:
- Risk of a loss of “fruitiness” linked to the degradation of acetate esters by Brettanomyces yeasts which develop late in distillation ciders.
- Presence in spirits of molecules (including allyl alcohol) which beyond their possibly negative organoleptic impact could have a negative impact on health.
The production of acrolein in ciders is closely linked to the metabolism of glycerol, one of the products of yeast metabolism during alcoholic fermentation and whose content in distilled ciders reaches approximately 5 g/L. This compound can be degraded at the end of alcoholic fermentation by certain lactic acid bacteria. This degradation of glycerol leads to organoleptic disorders by developing a bitter taste known as acroleic sting. If the production of acrolein is observed in numerous bacterial species in cider it is closely linked to the presence of a lactic acid bacteria, Secundilactobacillus collinoides, capable of converting glycerol into 3-hydroxypropionaldehyde (3-HPA), precursor of acrolein. Under conditions of acidic pH and/or high temperature, for example during the distillation of ciders for brandies, 3-HPA is transformed into acrolein by dehydration.
Previous work carried out as part of the MoNArC project (Modulation of Aromatic Notes of Calvados, Feder Innovation, 2017-2020) allowed us to constitute a collection of 72 strains of Secundiactobacillus (of which 70 belong to the collinoides species, one to species brevis and one to the species diolivorans) isolated from distillation ciders. Within this collection, two types of pdu operon (operon which codes for the enzymes involved in glycerol metabolism) were characterized: one (qualified as type I) similar to that of the reference S. collinoides strain LMG18850 known to degrade glycerol and the second (qualified as type II) associated with the reference S. collinoides strain DSM20515T, which does not degrade glycerol. All strains possessing the type I operon are capable of degrading glycerol while 31% of strains possessing the type II operon are incapable of doing so. Thus, 3 genetic and metabolic profiles could be highlighted. This work made it possible to establish a link between the production of acrolein and the presence of S. collinoides; however, the presence of this species in a cider is not sufficient to assess the risk of acrolein sting. To go further, a comparative analysis of eight genomes of S. collinoides strains isolated from ciders was also carried out within the framework of MoNArC. Genomic analyzes showed low variability in the main genomic characteristics between strains but a major difference in the organization of these two types of operons lies in the type of transcriptional regulator located upstream of the operon. For the first type of operon, the regulator is identified as PocR, while it is a regulator from the AraC family in the case of the second type of operon.
Thus, understanding the mechanisms of acrolein production in ciders remains a real problem which requires an analysis of subpopulations of S. collinoides, a study of the regulation of the expression of the pduC gene and the dynamics of microbial interaction. . The CELAD project is a continuation of research carried out within the MALIM team. After a necessary descriptive phase, the results and tools previously developed are available to carry out an in-depth scientific study on the influence of biotic and abiotic factors on the appearance of acroleic sting in ciders to be distilled. The MALIM team will build on the partnership it has established with the cider industry through previous projects.
Requirements
- Research Field
- Biological sciences » Biodiversity
- Education Level
- Master Degree or equivalent
Specific Requirements
Knowledge of molecular biology, microbial ecology and bioinformatics is required
- Research Field
- Biological sciences » Biodiversity
Additional Information
Selection process
Candidates selected on the basis of their academic results in Master 1 and Master 2 will be interviewed according to the following methods:
the candidate will have 10 minutes to present and his presentation must focus in particular on:
- a summary of the academic career;
- the place of the master's internship subject in the literature and the objectives of the host UR;
- the summarized and critical presentation of the master's results;
- the scientific and methodological perspectives of the thesis project;
- the place of the doctorate in the candidate's professional project.
This presentation will be followed by a 15-minute question period.
Additional comments
The job concerns a thesis offer for a period of three years
Work Location(s)
- Number of offers available
- 1
- Company/Institute
- Université de Caen Normandie
- Country
- France
- State/Province
- Normandy
- City
- CAEN
- Postal Code
- CS14032
- Street
- Esplanade de la Paix
- Geofield
Where to apply
[email protected]
Contact
- City
Caen- Website
https://abte.eu/index.php/presentation/- Street
Esplanade de la Paix 14032 CAEN CEDEX- Postal Code
CS 14032
[email protected]
STATUS: EXPIRED