Production of sulfur flavors by ten strains of Geotrichum candidum
ABSTRACT Ten strains of Geotrichum candidum were studied on a liquid cheese model medium for the production of sulfur compounds which contribute to the aroma of cheeses. The volatile components produced by each cultured strain were extracted by dynamic headspace extractions, separated and quantified by gas chromatography (GC), and identified by GC-mass spectrometry. It was shown that four strains of this microorganism produced significant quantities of S -methyl thioacetate, S -methyl thiopropionate, S -methyl thiobutanoate, S -methyl thio iso butanoate, S -methyl thio iso valerate, and S -methyl thiohexanoate. This is the first example of the production of these compounds by a fungus. In a…
Dialysis of flavour compounds: Yields of extraction on model solution
The extraction of 58 flavour compounds by Nafion membrane dialysis was studied using a model solution. Reproducibility and yield of the method were investigated. The coefficient of variation of the extraction yield was less than 15% for 48 of the 58 compounds tested. When the number of carbon atoms increased, the extraction yield fell to zero for compounds with more than ten carbon atoms. Flavour compounds with a cyclic structure showed a better diffusion rate through the membrane than other compounds with the same number of carbon atoms. The extraction yield seems to be correlated mainly to the hydrophobicity of the molecule. The use of the method for quantitative analysis was studied. Ext…
Comparison of odour sensory profiles performed by two independent trained panels following the same descriptive analysis procedures
Odour sensory profiling of 28 associations of cheese ripening micro-organisms was performed by two panels of 10 assessors on two different sites. Sample preparation, training protocols and references, tasting procedures and scoring were similar in the two laboratories. Panel 2 used 10 attributes and panel 1 used these terms plus 4 extra descriptors. Analysis of variance and multivariate methods (canonical variate analysis, generalised procrustes analysis and STATIS) exhibited differences between assessors within a panel and between panels concerning the use of the scoring scale and the strength of product discrimination by attribute. Panel 1 was more sensitive to fruity notes and panel 2 to…
Effect of culture parameters on the production of styrene (vinyl benzene) and 1-octene-3-ol by Penicillium caseicolum
SummaryPenicillium caseicolum has been shown to completely synthesize styrene. A medium was developed to test the capacity of different strains for this synthesis. In a synthetic medium, styrene production began only after the glucose was entirely consumed. This production depended on storage temperature and occurred simultaneously with 1-octene-3-ol formation.
Review : Compounds involved in the flavor of surface mold-ripened cheeses : Origins and properties
Abstract Cheese flavor is obtained through a series of chemical changes that occur in the curd during the early stages of ripening. Lipid hydrolysis leads to FFA, which serve as substrates for further reactions. Peptides and amino acids, which results from proteolysis, also lead to aroma compounds through enzymic and chemical reactions. This paper is a review of the current knowledge about the compounds that contribute to flavor in mold-ripened cheeses, especially Camembert-type cheese. Discussed are the pathway of formation, the sensory properties (odorous notes and perception thresholds), and the quantities of the main volatile compounds encountered in these types of cheeses.
Effect of the association of surface flora on the sensory properties of mould-ripened cheese
Summary - In cheese, flavour and taste are, in great part, generated by the starters during the ripening stage. Proteolysis and lipolysis are the first steps of the elaboration of a large number of taste and odour compounds directly invol ved in the sensory quality of cheeses. The pathways used by the microorganisms to produce flavour compounds are still unclear in many cases. It would be useful for the starter-producing industry to have screening criteria permitting diversification of the starter quality, and for the cheese industry to know which strain to associate to obtain cheeses with specifie sensory properties. The production of experimental cheeses with different associations of sur…
Regulation of the synthesis of aryl metabolites by phospholipid sources in the white-rot fungus Bjerkandera adusta
The white-rot basidiomycete Bjerkandera adusta was cultivated in a liquid medium enriched with l-phenylalanine and various phospholipid sources (lecithin, egg yolk and asolectin). Three aromatic metabolites (benzaldehyde, benzyl alcohol and benzoic acid) were produced under these culture conditions. High concentrations of benzaldehyde (404 mg l–1) were obtained when the cultures were supplemented with 10 g lecithin l–1. Benzyl alcohol production was promoted when the strain was grown with 5 or 10 g lecithin l–1. In the absence of or with a low concentration of lecithin (2.5 g l–1), benzoic acid was the major aryl metabolite synthesized. The results presented here indicate that aryl alcohol …
Volatile compounds produced by the ligninolytic fungus Phlebia radiata Fr. (Basidiomycetes) and influence of the strain specificity on the odorous profile
Abstract The odorous volatile compounds produced by 3 strains (out of 25 strains tested) of Phlebia radiata Fr. were investigated on six synthetic media and identified by GC-MS analysis. One of the 3 strains was odourless. Aromatic primary alcohols and a sesquiterpenic alcohol, α-bisabolol, were the most abundant metabolites for both of the other strains, which exhibited similar flavours and a similar gas chromatographic profile.
Methylthioacetaldehyde, a possible intermediate metabolite for the production of volatile sulphur compounds from L-methionine by Lactococcus lactis
Volatile sulphur compounds (VSCs) production from L-methionine was studied in Lactococcus lactis. In vitro studies with radiolabelled L-methionine and resting cells of L. lactis revealed that L-methionine was initially converted to alpha-keto-gamma-methylthiobutyrate (KMBA) by a transamination reaction. A part of KMBA was subsequently chemically converted to methylthioacetaldehyde, methanethiol and dimethylsulphides. Chemical conversion of KMBA to methylthioacetaldehyde was dependent on pH, Mn(II) and oxygen. Since methanethiol and dimethylsulphide production was highly related to that of methylthioacetaldehyde, the latter compound was proposed as being an intermediate in VSCs production by…