Jean-Louis Berdagué

Volatile components of dry cured Iberian ham

Abstract A study was conducted to identify the volatile compounds in aged Iberian hams, processed in the traditional way. The volatiles from aged hams were entrained in cold traps after distillation under high vacuum. The distillate was collected with dichloromethane and analysed by gas-chromatography-mass-spectrometry (GC-MS). Seventy-seven compounds were tentatively identified in the volatile fraction. Alkanes (12), branched alkanes (14), aldehydes (13), and aliphatic alcohols (9) dominated the volatiles. Small amounts of lactones (5), esters (9) and ketones (7) and other miscellaneous compounds were also present. The possible origins of these compounds and their relationship with the characteristic flavour of this product are discussed.

Lipolysis, proteolysis and formation of volatile components during ripening of a fermented sausage with Pediococcus pentosaceus and Staphylococcus xylosus as starter cultures

Bacterial growth, formation of acids, lipolysis, proteolysis, fat oxidation, formation of volatile compounds and flavour characteristics were followed during ripening and storage of a fermented sausage. The starter culture used was composed of Pediococcus pentosaceus and Staphylococcus xylosus. The number of Pediococcus sp. increased by 1.5 log cfu/g during the first day of processing and remained constant at this level for 3 weeks. The corresponding initial increase in the numbers of Staphylococcus sp., 0.4 log cfu/g, was followed by a rapid decrease in the viable numbers. Lactic acid, mainly d-lactic acid, and acetic acid were formed during ripening. The triglycerides were hydrolysed to 1,2-diglycerides and free fatty acids at the beginning of ripening, followed by the formation of 1,3-diglycerides and monoglycerides, indicating lipolytic activity. Moreover, the nonprotein nitrogen increased during ripening as a result of the proteolytic activity. Most of the changes with respect to pH, formation of d-lactic acid, acetic acid, peroxides and flavour development occurred during the initial 3 days of ripening, when growth of Pediococcus sp. and Staphylococcus sp. occurred. Lipolysis as well as proteolysis continued after this initial period. The volatile compounds identified belonged to several chemical families, viz. aliphatic and aromatic hydrocarbons, aldehydes, ketones, alcohols, phenols, carboxylic acids, esters, nitrogen compounds, sulphur compounds, chloride compounds, terpenes and furans. Many of the volatile compounds probably originated from smoke and seasoning (onion/garlic and pepper), while others were a result of the activities of muscle enzymes and bacteria.

Desorbed terpenes and sesquiterpenes from forages and cheeses

The composition and sensory characteristics of matured cheeses are controlled by a number of factors, among which the type of feed is important. The influence of feeding can be reflected by the presence in cheeses of terpenes and sesquiterpenes, compounds typically indicating their vegetable origin (Mariaca et al . 1997). Indeed, several investigators have already established that these compounds could characterize the forage even to a specific geographical location. Dumont & Adda (1978), Dumont et al . (1981), Guichard et al . (1987), Bosset et al . (1994) and Moio et al . (1996) were thus able to distinguish cheeses from lowland and upland regions. In most of these studies, the conditions under which milk was produced and processed were not completely controlled. Furthermore, all these studies analysed only the volatile fraction of cheeses and did not examine the volatile compounds in the forages used. Recently Bosset et al . (1994), in one part of the project described by Jeangros et al . (1997), showed that highland grass with a highly diversified botanical composition produces milk and cheeses with significantly different chemical compositions from those from lowland grass. To improve our understanding of the relationship between animal feed and cheese composition, we have investigated under controlled experimental conditions both the composition of the terpene and sesquiterpene fractions of four forages with different botanical diversities and the influence of those forages on the terpene fraction of cheeses.

Production of flavor esters by lipases of Staphylococcus warneri and Staphylococcus xylosus

The present paper describes the potential of Staphylococcus warneri and Staphylococcus xylosus lipases in the production of a variety of flavor esters. Both immobilized lipases produced ethyl esters from hexanoic to oleic acids with an optimum at decanoic acid. They esterified aliphatic and branched chain primary alcohols from ethanol to hexanol. Under our standard conditions, acetic, butyric, 2-methyl butyric, 3-methyl butyric, and valeric acids underwent slight esterification.

Rapid discrimination of meat products and bacterial strains using semiconductor gas sensors

The aim of this study is to test, in ambient conditions, the capacities of semiconductor gas sensors to discriminate cured products (dry sausages of various origins or cured hams of different qualities) as well as aromatic or pathogenic bacterial strains commonly used for curing or sometimes encountered in meat products. An overall analysis of the dynamic headspace desorbed by the different substrates analysed has been carried out by six gas sensors with different characteristics. Using factorial discriminant analysis, we classify 94% of dry sausages, 87% of cured hams and 98% of bacterial strains into their respective groups. Cross-validation of the discriminant functions confirms the stability of the results. The results of this study show that with a limited number of semiconductor gas sensors, it is possible to classify rapidly and reliably various products, on the basis of the volatile compounds which they desorb.

Fast characterization of foodstuff by headspace mass spectrometry (HS-MS)

Abstract The field of the rapid characterization of products by HS-MS is reviewed. The general principle of HS-MS systems consists of introducing volatile components present in the HS of a sample without prior chromatographic separation into the ionization chamber of a mass spectrometer. The spectrum resulting from simultaneous ionization and fragmentation of the mixture of molecules introduced constitutes a “fingerprint” that is characteristic of the product being analyzed. Exploitation of this spectral information allows one determine the composition of the sample.

Comparative Analysis of Extracellular and Intracellular Proteomes of Listeria monocytogenes Strains Reveals a Correlation between Protein Expression and Serovar

ABSTRACT Listeria monocytogenes, the etiologic agent of listeriosis, remains a serious public health concern, with its frequent occurrence in food environments coupled with a high mortality rate. Among the 13 serovars, human listeriosis is mostly associated with the serovar 4b, 1/2b, and 1/2a strains. To investigate the diversity of L. monocytogenes, the intracellular and extracellular proteins of 12 strains were analyzed by two-dimensional gel electrophoresis. These strains had different origins, belonged to different serovars (4b, 1/2a, and 1/2b), and presented with different levels of virulence in chicken embryos. The clustering of the strains in two groups based on proteomic patterns is in agreement with the L. monocytogenes phylogenetic lineages. Statistical analysis did not allow for identification of proteins specific to the isolate origin or the virulence level of the strains, but 26 and 21 protein spots were shown to be significantly overexpressed and underexpressed, respectively, in the six strains of serovar 1/2a (lineage II) compared to strains of serovar 1/2b or 4b. Moreover, a penicillin-binding protein was specific for serovar 1/2b and two protein spots identified as a serine protease were specific to serovar 4b. These protein spots, identified through peptide mass fingerprinting using matrix-assisted laser desorption ionization-time of flight mass spectrometry, were essentially found in the extracellular proteome and may have uses as potential markers for serotyping and risk analysis.

Effect of nitrite on the odourant volatile fraction of cooked ham

The aim of this work was to reliably identify the key odour compounds in cooked ham and acquire new knowledge on the role of sodium nitrite on the formation of its aroma. Gas chromatography coupled with mass spectrometry and (or) olfactometry was used. In all, 24 odourants were identified in the volatile fraction of cooked ham. Their main origins are discussed. Orthonasal sniffing of the hams was used to study how these substances contributed to the overall aroma of the product. The aroma of cooked ham is a balance between that of certain sulfur compounds produced during cooking and that of oxidation compounds commonly found in cooked meats. In the absence of nitrite, this balance is disturbed by extensive formation of oxidation compounds that mask the meaty notes induced by the sulfur compounds.

Fast characterization of Camembert cheeses by static headspace-mass spectrometry

Abstract An application of the static headspace–mass spectrometry (SHS–MS) method for the rapid characterization of cheeses was described. After an equilibration step, the volatile components of the headspace were injected directly into a mass spectrometer via a short transfer line. The mass spectrum thereby obtained, without prior chromatographic separation, represents a “fingerprint” of the analyzed product. For data analysis the mass fragments of each spectrum were taken as potential descriptors of the headspace composition. Five batches of cheeses of the Camembert-type were classified by factorial discriminant analysis to evaluate the discriminating power of SHS–MS. The effect of heating duration and temperature on the overall signal intensity and on the abundance of some specific fragments (water, sulfur compounds, ketones) was studied. The results show that the analysis of samples at ambient temperature affords the best classification of the cheese batches. Even so, the amounts of the volatile components extracted by static headspace are small and so limit the discriminating power of this system.

Rapid discrimination of Micrococcaceae species using semiconductor gas sensors

Abstract The headspace generated by bacteria grown in an agar medium (APT) was analyzed by a 6 gas sensor array. The bacterial species studied were the following: Staphylococcus carnosus, Staphylococcus xylosus, Staphylococcus saprophyticus, Staphylococcus warneri, Staphylococcus epidermidis, Staphylococcus aureus and Micrococcus varians. A statistical analysis of the signals by factorial discriminant analysis meant it was possible to classify 100% of bacterial species into their respective groups. A cross-validation of the discriminating axes classified 90.5% of bacterial strains. These results show that gas sensors are an efficient tool for the discrimination of bacteria in culture.