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Key enzymes and metabolic pathways involved in the biosynthesis of 3-methylbutanal from leucine catabolism among LAB
The catabolism of leucine during cheese ripening is mainly initiated by the action of microbial aminotransferases, although chemical degradation (Strecker degradation) can also occur (Ardo, 2006; Smit et al., 2009; Yvon et al., 1997; Yvon and Rijnen, 2001). Among LAB, the deamination of glutamate to α-ketoglutarate (α-KG) catalyzed by glutamate dehydrogenase (GDH) is usually linked to a transamination route.
Aminotransferase and glutamate dehydrogenase
Aminotransferase activity (AT) was found to be present in a large group of cheese related LAB. Activities varied and diversity existed among the strains (Brandsma et al., 2008; Fernández de Palencia et al., 2006; Smit et al., 2004; Yvon et al., 1997). Yvon et al. (1997) purified and characterized the major aromatic aminotransferase (AraT) from L. lactis and demonstrated the role of this enzyme in the initiation of degradation of several amino acids including leucine, which was responsible for the synthesis of precursors of aroma compounds usually found active under cheese ripening conditions. Moreover, it was found to exhibit overlapping substrate specificities towards both branched chain and aromatic amino acids (Yvon et al., 1997; Yvon and Rijnen, 2001). The role of both aromatic and branched chain aminotransferases (AraT/BcaT) was studied by Rijnen et al. (2003) in a cheese model and it was demonstrated that both BcaT and AraT were involved in the degradation of leucine. Leucine was converted into α-ketoisocaproate by aminotransferase enzyme and during this conversion the amino group of leucine was transferred to α-ketoglutarate resulted in the formation of glutamic acid.
To intensify cheese aroma, Tanous et al. (2002) pointed the importance of GDH activity as major criterion for the selection of flavour-producing LAB strains. Later on, a beneficial effect on aroma formation was observed by using a combination of GDH positive lactobacilli with L. lactis ssp. cremoris NCDO763 (Kieronczyk et al., 2004). Tanous et al. (2005) explored the biosynthetic pathways for α-KG formation and its impact on cheese aroma development and it has been shown that the citrate-oxaloacetate pathway, that requires citrate permease (CitP), citrate lyase (CitL) and aspartate aminotransferase, was operative for L. lactis ssp. diacetylactis and hence stimulated the conversion of amino acids.
Major metabolic pathways for the biosynthesis of 3-methylbutanal
The transamination of leucine results in α-ketoisocaproate, which is the central metabolite in leucine catabolism (Smit et al., 2004), and gives rise to 3-methylbutanal either directly as a result of non-oxidative decarboxylation by α-ketoacid decarboxylase (KADC) or indirectly via an oxidative decarboxylation by the activity of α-ketoacid dehydrogenase (KADH) (Helinck et al., 2004; Larrouture-Thiveyrat and Montel, 2003). In the literature, the direct pathway for the biosynthesis of 3-methylbutanal was very well documented in LAB. On the contrary, the indirect pathway was not studied extensively (Table 1).
Regulation of 3-methylbutanal biosynthesis
The biosynthesis of 3-methylbutanal in bacteria depends on the functionality of intracellular pathways and is mainly regulated by redox environment (NAD+/NADH, H+ yield, presence/absence of oxygen). Indeed, high formation of 3-methylbutanal in L. lactis (Kieronczyk et al., 2006) and Proteus vulgaris (Deetae et al., 2011) has been attributed towards the presence of oxygen or stimulation of KADC enzyme activity.
Presence and role of 3-methylbutanal in various varieties of cheeses
An overview of previous studies on flavour characteristics of some cheeses revealed the presence and crucial role of 3-methylbutanal for the unique flavour development in these cheese types (Table 2).
The presence of Strecker aldehydes in hard cheddar cheese made from cow’s pasteurized milk was reported to be responsible for a nutty/balanced flavour and was considered as desirable (Avsar et al., 2004; Hannon et al., 2006). However, on the contrary, Egyptian Ras and Manchego cheese usually made from either cow/buffalo/sheep’s raw milk revealed an unclean/burnt flavour (Ayad et al., 2004a; Centeno et al., 2002), which was considered as non desirable. This unclean/burnt flavour was attributed to the high levels of aldehydes and alcohols and was related to the poor quality milk used for cheese manufacture. The flavour perception and desirability of aldehydes in Parmigiano Reggiano, Parmesan and Roncal cheese made from either cow/sheep’s raw and pasteurized milk were not clearly reported (Barbieri et al., 1994; Bosset and Gauch, 1993; Irigoyen et al., 2007).
The perceived chocolate-like aroma after six weeks of cheese ripening in semi-hard Proosdij-type cheese made from cow’s pasteurized milk using a mesophilic strain L. lactis ssp. lactis B851 with acidifying mesophilic and an adjunct thermophilic culture was attributed to the presence of high concentration of 3-methylbutanal (Ayad et al., 2003). A similar chocolate-like flavour was perceived as well in Gouda/Proosdij type cheese and was considered as desirable (Engels et al., 1997; Van Leuven et al., 2008). During the study of aroma development in reduced-fat semi-hard cheese using culture adjunct of Lactobacillus paracasei (CHCC 4256), 4 times higher concentration of aldehydes and alcohols were determined as compared to controls but flavour perception/desirability was not clearly mentioned (Thage et al., 2005). Some wild strains of L. lactis isolated from ewes’ raw milk cheeses were reported to produce high levels of aldehydes and alcohols, which were considered as responsible for abnormal odours (Morales et al., 2003).
Aldehydes and alcohols were generally present and considered as potent odorants in soft cheeses. At low concentrations, they were perceived as a fruity flavor and considered desirable, while at high concentration, they resulted in rather off-flavour and highly non desirable (Sable and Cottenceau, 1999). The impact of various microorganisms on aromatic profiles of soft cheese has started to be elucidated (Bintsis and Robinson, 2004; Deetae et al., 2009; Irlinger et al., 2012; Massouras et al., 2006). A richer pattern of aroma compounds namely aldehydes, alcohols and esters were achieved using L. paracasei subsp. paracasei and Debaryomyces hansenii as adjuncts in the manufacture of Feta-type cheese (Bintsis and Robinson, 2004). During the study of aromatic profile of Teleme cheese made from either sheep’s or goat’s milk or a combination of both, Massouras et al. (2006) found the highest level of volatile compounds in cheese made from sheep’s milk.
Table of contents :
Chapitre I : Synthèse bibliographique
I. Le genre Carnobacterium
The genera Carnobacterium
Abstract
1. Introduction
2. Characteristics of the genus and relevant species
3. Identification tools
4. Importance of the genus and individual species in the food industry
Further Reading
Carnobacterium maltaromaticum: Identification, isolation tools, ecology and technological aspects in dairy products
Abstract
1. Introduction
2. Taxonomy
3. Identification tools
4. C. maltaromaticum in dairy products
5. Preservation
6. Safety assessment
7. Potential interest in cheese technology
References
Biosynthesis and role of 3-methylbutanal in cheese: major metabolic pathways, enzymes involved and strategies for control
Abstract
1. Introduction
2. Key enzymes and metabolic pathways involved in the biosynthesis of 3-methylbutanal from leucine catabolism among LAB
3. Presence and role of 3-methylbutanal in various varieties of cheeses
4. Strategies for control of 3-methylbutanal concentration in cheese
5. Conclusions
Chapitre II : Résultats
I.1 Introduction
I.2 Carnobacterium maltaromaticum: Impact and interaction as a barrier species against the undesired flora of soft cheese
Abstract
1. Introduction
2. Material and methods
3. Results
4. Discussion
5. Conclusion and perspectives
References
I.3 Contributions de l’article
II. Identification de la voie de biosynthèse du 3-méthylbutanal à partir du catabolisme de la leucine chez Carnobacterium maltaromaticum LMA 28
II.1 Introduction
II.2 Identification of metabolic pathways involved in the biosynthesis of flavor compound 3 methylbutanal from leucine catabolism by Carnobacterium maltaromaticum LMA 28
Abstract
1. Introduction
2. Material and methods
3. Results
4. Discussion
5. Conclusion and perspectives
References
II.3 Contributions de l’article
III. Effet de l’oxygène sur la biosynthèse du 3-méthylbutanal chez Carnobacterium maltaromaticum LMA 28
III.1 Introduction
III.2 Effect of oxygen on the biosynthesis of flavor compound 3-methylbutanal from leucine catabolism during batch culture in Carnobacterium maltaromaticum LMA 28
1. Introduction
2. Material and methods
3. Results and discussion
4. Conclusion
References
III.3 Contributions de l’article
Chapitre III : Conclusion générale et perspectives
Références bibliographiques
Annexes
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