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Lactic acid bacteria (LAB) have the enzyme potential to transform amino acids into aroma compounds that contribute greatly to cheese flavour. Generally, amino acid conversion by LAB is limited by their low production of α-ketoglutarate since this α-ketoacid is essential for the first step of the conversion. Indeed, we have demonstrated that adding exogenous α-ketoglutarate to cheese curd, as well as using a genetically modified L. lactisstrain capable of producing α-ketoglutarate from glutamate, greatly increased the conversion of amino acid to potent aroma compounds in cheese. Here we report the presence of glutamate dehydrogenase (GDH) activity required for the conversion of glutamate to α-ketoglutarate in several ‘natural’ LAB strains, commonly used in cheese manufacturing. Moreover, we show that the ability of LAB to produce aroma compounds from amino acids is closely related to their GDH activity. Therefore, GDH activity appears to be a major criterion for the selection of flavour-producing LAB strains, which could be used as a starter or as an adjunct to intensify flavour formation in some cheeses.

l‐Methionine degradation products and catabolic enzymatic activities involved in methanethiol generation were investigated in Geotrichum candidumGcG. l‐Methionine was easily degraded by G. candidumand the transamination product, 4‐methylthio‐2‐oxobutyric acid (KMBA), was found to transiently accumulate. In parallel, considerable l‐methionine aminotransferase activity was found in this microorganism. l‐Methionine and KMBA demethiolating activities were also detected. The degradation of KMBA corresponded to an overall increase in the production of volatile sulfur compounds. These results show that the transamination pathway is of major importance in the initial breakdown of l‐methionine by this cheese‐ripening microorganism.

Volatile sulphur compounds are major flavouring compounds in many traditional fermented foods including cheeses. These compounds are products of the catabolism of L-methionine by cheese-ripening microorganisms. The diversity of L-methionine degradation by such microorganisms, however, remains to be characterized. The objective of this work was to compare the capacities to produce volatile sulphur compounds by five yeasts, Geotrichum candidum, Yarrowia lipolytica, Kluyveromyces lactis, Debaryomyces hansenii, Saccharomyces cerevisiae and five bacteria, Brevibacterium linens, Corynebacterium glutamicum, Arthrobacter sp., Micrococcus luteus and Staphylococcus equorum of technological interest for cheese-ripening. The ability of whole cells of these microorganisms to generate volatile sulphur compounds from L-methionine was compared. The microorganisms produced a wide spectrum of sulphur compounds including methanethiol, dimethylsulfide, dimethyldisulfide, dimethyltrisulfide and also S-methylthioesters, which varied in amount and type according to strain. Most of the yeasts produced methanethiol, dimethylsulfide, dimethyldisulfide and dimethyltrisulfide but did not produce S-methylthioesters, apart from G. candidum that produced S-methyl thioacetate. Bacteria, especially Arth. sp. and Brevi. linens, produced the highest amounts and the greatest variety of volatile sulphur compounds including methanethiol, sulfides and S-methylthioesters, e.g. S-methyl thioacetate, S-methyl thiobutyrate, S-methyl thiopropionate and S-methyl thioisovalerate. Cell-free extracts of all the yeasts and bacteria were examined for the activity of enzymes possibly involved in L-methionine catabolism, i.e. L-methionine demethiolase, L-methionine aminotransferase and L-methionine deaminase. They all possessed L-methionine demethiolase activity, while some (K. lactis, Deb. hansenii, Arth. sp., Staph. equorum) were deficient in L-methionine aminotransferase, and none produced L-methionine deaminase. The catabolism of L-methionine in these microorganisms is discussed.

Tryptic digests of fragment A299 585of penicilloylated serum albumin obtained from two penicillin‐treated patients or prepared by in vitro conjugation, were analyzed by a tandem immunoaffinity reversed‐phase HLPC. Determinations of benzyl penicilloyl groups (BPO) were performed on the different fractions. Three BPO containing peptides were identified by their amino acid sequence and the bound BPO were located on lysines 432, 541 and 545. Six major BPO binding sites were thus identified on the whole albumin molecule. All of them are lysine residues and correspond to a limited number of definite structures in which lysine and serine residues appear to be closely associated.

Tryptic digests of fragment A 299 585of penicilloylated serum albumin obtained from two penicillin-treated patients or prepared by in vitro conjugation, were analyzed by a tandem immunoaffinity reversed-phase HLPC. Determinations of benzyl penicilloyl groups (BPO) were performed on the different fractions. Three BPO containing peptides were identified by their amino acid sequence and the bound BPO were located on lysines 432, 541 and 545. Six major BPO binding sites were thus identified on the whole albumin molecule. All of them are lysine residues and correspond to a limited number of definite structures in which lysine and serine residues appear to be closely associated.

The enzymatic degradation of amino acids in cheeses is believed to generate aroma compounds. In lactococci, transamination is the f?rst step in the degradation of aromatic and branched-chain amino acids. Several aminotransferase activities have been detected and. an aromatic-aminotranferase has been purified and characterised. Ketoacids resulting from transamination are mainly degraded to carboxylic acids or to hydroxyacids, depending on the reaction conditions. These degradations could be catalysed by lactate dehydrogenase and pyruvate dehydrogenase which are involved in pyruvate catabolism. However, we also suggest the existence of other dehydrogenases, more specific for ketoacids from amino acids. Whereas amino acids catabolism need to be clarified, we can state that lactococci have the enzymatic equipment required for the transformation of aromatic and branched chain amino acids to volatile aroma compounds. ? Inra / Elsevier, Paris.La d?gradation enzymatique des acides amin?s est une voie possible pour la formation de mol?cules aromatiques dans les fromages. Chez les lactocoques, la transamination est la premi?re ?tape de d?gradation des acides amin?s aromatiques et des acides amin?s ? cha?ne ramifi?e. Plusieurs aminotransf?rases ont ?t? mises en ?vidence et. en particulier, une aminotransferase aromatique a ?t? purifi?e et caract?ris?e. Les c?toacides form?s au cours de la transamination sont ensuite essentiellement d?grad?s en acide, en absence de glucose, ou en hydroxyacide. en pr?sence de glucose. Ces d?gradations pourraient ?tre catalys?es par la lactate dehydrogenase et la pyruvate dehydrogenase intervenant dans le catabolisme du pyruvate. Toutefois, l'existence d'autres dehydrogenases plus sp?cifiques des c?toacides issus des acides amin?s est sugg?r?e. Bien que le catabolisme des acides amin?s ne soit pas encore totalement ?lucid?, la mise en ?vidence de ces activit?s de d?gradation des acides amin?s nous permet d'affirmer, d'ores et d?j?, que les lactocoques ont le potentiel enzymatique n?cessaire ? la d?gradation des acides amin?s aromatiques et des acides amin?s ? cha?ne ramifi?e en mol?cules volatiles aromatiques. ? Inra / Elsevier, Paris.

Benzyl penicilloyl groups (BPO) derive from penicillin G by cleavage of the β lactam ring; they covalently bind to proteins to give conjugates which have lost all antibiotic properties but are considered as the major allergenic determinants in penicillin allergy. A solid-phase Enzyme Immuno Assay (EIA) of BPO groups in different biological fluids is described. It is a competitive immunoassay using acetylcholinesterase as label. In all biological fluids, very low non-specific binding values are observed. The sensitivity and the precision of the assay are good since ca. 0.5 ng/ml can be measured with a coefficient of variation less than 10%. Cross reactions between BPO and penicillin or penicillin derivatives are nil or very low. This assay is more sensitive, much more rapid and easier to handle than the other methods available and is thus suitable for routine determinations. In association with reversed-phase high performance liquid chromatography this EIA has allowed an initial investigation of the location of BPO-binding sites on micro quantities of serum albumin (ca. 1 mg) from penicillin treated patients.

Tryptic digests of fragment C 124–298of penicilloylated serum albumin, obtained from a penicillin-treated patient or prepared by in vitro conjugation, were analyzed by HPLC. Determinations of benzyl penicilloyl groups (BPO) were performed on the different fractions. Three BPO-containing peptides were identified by their amino acid sequence and the bound BPO was located on lysines 190, 195 and 199 and serine 193. These four main BPO-binding sites are all located on a very short region (10 amino acid residues) of the albumin molecule at the junction of domains 1 and 2.

Cyanogen bromide and tryptic fragments of penicilloylated serum albumin from penicillin-treated patients were separated by HPLC. Determinations of benzylpenicilloyl (BPO) were performed on the different fractions. A BPO containing peptide was identified by its amino acid sequence and the bound BPO group was located on the lysine residue 199.

Tryptic digests of fragment C124–298of penicilloylated serum albumin, obtained from a penicillin‐treated patient or prepared by in vitro conjugation, were analyzed by HPLC. Determinations of benzyl penicilloyl groups (BPO) were performed on the different fractions. Three BPO‐containing peptides were identified by their amino acid sequence and the bound BPO was located on lysines 190, 195 and 199 and serine 193. These four main BPO‐binding sites are all located on a very short region (10 amino acid residues) of the albumin molecule at the junction of domains 1 and 2.

The efficiency of colostral protein digestion was studied in nine newborn lambs fed one meal of bovine colostrum 3 h after birth. The results were compared with those obtained in two unfed lambs and four lambs fed bovine milk. The protein and peptide composition [immunoglobulins G1 (IgG1), β-lactoglobulin, α-lactalbumin, caseins and peptides resulting from casein hydrolysis] of digesta, gastrointestinal tissues, blood and urine were determined in samples taken 0.75 or 4 h after feeding. The amounts of ingested proteins in lambs fed colostrum were much higher than in those fed the milk diet, and their abomasal emptying was faster. α-Lactalbumin was highly degraded by abomasal and intestinal proteases, whereas β-lactoglobulin and in particular the immunoglobulins were less sensitive. The gastric emptying of caseins was delayed in and the kinetics of appearance of peptides originating from casein hydrolysis was comparable to that observed in lambs fed milk and in 1-mo-old preruminant calves. Thirty-five percent of dietary amino acids ingested as colostrum were available within 4 h for amino acid metabolism; this percentage was 54% in the milk-fed lambs. In the lambs fed colostrum, these amino acids were provided by β-lactoglobulin, casein and IgG1 (0.52, 0.43 and 0.30 g/kg body wt, respectively), whereas in milk-fed animals casein and β-lactoglobulin were the most important sources of these amino acids (0.40 and 0.20 g/kg, respectively).

Cyanogen bromide and tryptic fragments of penicilloylated serum albumin from penicillin‐treated patients were separated by HPLC. Determinations of benzylpenicilloyl (BPO) were performed on the different fractions. A BPO containing peptide was identified by its amino acid sequence and the bound BPO group was located on the lysine residue 199.

l-Methionine degradation products and catabolic enzymatic activities involved in methanethiol generation were investigated in Geotrichum candidum GcG. l-Methionine was easily degraded by G. candidum and the transamination product, 4-methylthio-2-oxobutyric acid (KMBA), was found to transiently accumulate. In parallel, considerable l-methionine aminotransferase activity was found in this microorganism. l-Methionine and KMBA demethiolating activities were also detected. The degradation of KMBA corresponded to an overall increase in the production of volatile sulfur compounds. These results show that the transamination pathway is of major importance in the initial breakdown of l-methionine by this cheese-ripening microorganism.