Catabolism of leucine to branched-chain fatty acids in Staphylococcus xylosus

Abstract

Aims: Staphylococcus xylosus is an important starter culture in the production of flavours from the branched-chain amino acids leucine, valine and isoleucine in fermented meat products. The sensorially most important flavour compounds are the branched-chain aldehydes and acids derived from the corresponding amino acids and this paper intends to perspectivate these flavour compounds in the context of leucine metabolism. Methods and Results: GC and GC/MS analysis combined with stable isotope labelling was used to study leucine catabolism. This amino acid together with valine and isoleucine was used as precursors for the production of branched-chain fatty acids for cell membrane biosynthesis during growth. A 83AE3% of the cellular fatty acids were branched. The dominating fatty acid was anteiso-C 15:0 that constituted 55% of the fatty acids. A pyridoxal 5¢-phosphate and a-ketoacid dependent reaction catalysed the deamination of leucine, valine and isoleucine into their corresponding a-ketoacids. As a-amino group acceptor a-keto-b-methylvaleric acid and a-ketoisovaleric acid was much more efficient than a-ketoglutarate. The sensorially and metabolic key intermediate on the pathway to the branched-chain fatty acids, 3-methylbutanoic acid was produced from leucine at the onset of the stationary growth phase and then, when the growth medium became scarce in leucine, from the oxidation of glucose via pyruvate. Conclusions: This paper demonstrates that the sensorially important branched-chain aldehydes and acids are important intermediates on the metabolic route leading to branched-chain fatty acids for cell membrane biosynthesis. Significance and Impact of the Study: The metabolic information obtained is extremely important in connection with a future biotechnological design of starter cultures for production of fermented meat.

Branched chain aldehydes: production and breakdown pathways and relevance for flavour in foods

“…Yvon et al (1999) were the first to show that adding α-keto glutarate to cheese curd leads to increased flavour levels due to increased transamination capacity. Later, this was also shown for other cheese types and for sausages (Larrouture et al 2000;Banks et al 2001;Ur-Rehman and Fox 2002;Beck et al 2004;Herranz et al 2004;Tjener et al 2004a;Williams et al 2004). Instead of adding α-ketoglutarate to cheese, the α-ketoglutarate can be recycled using the enzyme glutamate dehydrogenase (GDH,4).…”

Mesophilic and Psychrotrophic Bacteria from Meat and Their Spoilage Potential In Vitro and in Beef

“…3-Methyl-1-butanol (isoamyl alcohol, which was present in an M42-inoculated sample at 30 days also as isoamyl acetate) could derive from the proteolytic activity of the strains and from leucine catabolism (57). In fact, small-branched alcohols and aldehydes are key intermediates in the branched-chain amino acid catabolism, which can serve various purposes, such as the formation of branched-chain fatty acids for cell membrane synthesis in several microbial species (3,44,57). Sulfur compounds usually arise from sulforated amino acids catabolism (2,44).…”

The Use of Starter Cultures in Traditional Meat Products

“…Besides, other authors have described the capability of S. xylosus and S. carnosus strains to modulate aroma through the degradation of amino acids and free fatty acids (FFAs) [55][56][57].…”