M.J. Fernández

Factors influencing biogenic amines accumulation in dairy products

Fermented foods are among the food products more often complained of having caused episodes of biogenic amines (BA) poisoning. Concerning milk-based fermented foods, cheese is the main product likely to contain potentially harmful levels of BA, specially tyramine, histamine, and putrescine. Prompted by the increasing awareness of the risks related to dietary uptake of high biogenic amine loads, in this review we report all those elaboration and processing technological aspects affecting BA biosynthesis and accumulation in dairy foods. Improved knowledge of the factors involved in the synthesis and accumulation of BA should lead to a reduction in their incidence in milk products. Synthesis of BA is possible only when three conditions converge: (i) availability of the substrate amino acids; (ii) presence of microorganisms with the appropriate catabolic pathway activated; and (iii) environmental conditions favorable to the decarboxylation activity. These conditions depend on several factors such as milk treatment (pasteurization), use of starter cultures, NaCl concentration, time, and temperature of ripening and preservation, pH, temperature, or post-ripening technological processes, which will be discussed in this chapter.

Biogenic amines degradation by Lactobacillus plantarum: toward a potential application in wine

Biogenic amines (BA) in wine represent a toxicological risk for the health of the consumer, with several trade implications. In this study 26 strains of Lactobacillus plantarum were analyzed for their ability to degrade BA commonly found during wine fermentation. Two strains of L. plantarum were selected in reason of their ability to degrade putrescine and tyramine. The degradation was assessed in vitro, both in presence of the BA and in presence of the specific chemical precursor and of producer bacteria. The two L. plantarum biotypes were found capable to work synergically. In addition, the survival in wine-like medium and the aptitude to degrade malic acid after alcoholic fermentation of the selected L. plantarum strains was analyzed. Our results suggest the potential application of wine L. plantarum strains to design malolactic starter cultures able to degrade BA in wine.

Bifidogenic effect and stimulation of short chain fatty acid production in human faecal slurry cultures by oligosaccharides derived from lactose and lactulose

Bifidogenic effect and stimulation of short chain fatty acid (SCFA) production by fractions of oligosaccharides with a DP> or =3 and Gal beta(1-6) linkages synthesised from lactose or lactulose by Pectinex Ultra SP-L and Lactozym 3000 L HP G were evaluated in human faecal slurries. Results were compared with those obtained for the commercial oligosaccharide mixture Vivinal-GOS. Quantitative real-time PCR showed that all galacto-oligosaccharide (GOS) fractions stimulated slightly higher bifidobacteria growth than lactose, lactulose and Vivinal-GOS. GOS fractions promoted the production of total SCFA and acetic acid in a similar way to Vivinal-GOS and more than glucose, lactose and lactulose. In conclusion, oligosaccharides derived from lactose and lactulose may represent a suitable alternative to lactulose for the design of new functional food ingredients.

Isolation and characterization of tyramine-producing Enterococcus faecium strains from red wine.

Enterococcus faecium strains were isolated from red wines undergoing malolactic fermentation and identified by comparison of their 16S rDNA gene sequences with those included in the GenEMBL Databases. The tyrosine decarboxylase gene was identified in all the strains analysed by PCR using gene-specific primers and the ability to produce tyramine in a synthetic media was analysed by RP-HPLC. Survival of an E. faecium strain was also evaluated in microvinification assays using two different musts with different ethanol concentrations (10% and 12% (v/v)). Tyramine production was monitored during the vinification trials. Our results suggest that E. faecium strains isolated from wine are able to produce tyramine and tolerate wine conditions following a pre-acidic stress.

Role of Tyramine Synthesis by Food-Borne Enterococcus durans in Adaptation to the Gastrointestinal Tract Environment

ABSTRACT Biogenic amines in food constitute a human health risk. Here we report that tyramine-producing Enterococcus durans strain IPLA655 (from cheese) was able to produce tyramine under conditions simulating transit through the gastrointestinal tract. Activation of the tyramine biosynthetic pathway contributed to binding and immunomodulation of enterocytes.

Hydrosilylation of alkenes by iridium complexes

Abstract Iridium complexes prepared by reaction of binuclear 1,5-cycloocta-diene (COD) compounds of the type [IrX(COD) 2 ] (X = OMe, Cl) with monodentate Group Vb atom donor ligands (NPh 3 , PPh 3 , AsPh 3 , SbPh 3 ) yield a mixture of hexenyl(triethyl)silanes as well as the expected hexyl-(triethyl)silane from the catalytic hydrosilylation of hex-1-ene by triethyl-silane, in 1,2-dichloroethane at 60 °C. The most effective catalysts are those derived from [IrCl(COD)] 2 + 2 PPh 3 + 2 AsPh 3 and [Ir(OMe)(COD)] 2 + 2 As-Ph 3 . The latter system has been also found to be active for hydrosilylation reactions involving ethylene and propylene. The catalyst systems studied include [IrX(COD)] 2 + 2 L (X = OMe, L = NPh 3 , PPh 3 , AsPh 3 , SbPh 3 ; X = Cl , L = PPh 3 , AsPh 3 ), [Ir(OMe)(COD)] 2 + 4L (L = PPh 3 , AsPh 3 ) and [IrX(COD)] 2 + 2 PPh 3 + 2 AsPh 3 (X = OMe, Cl).

Differentiation of red wines using an electronic nose based on surface acoustic wave devices

An electronic nose, utilizing the principle of surface acoustic waves (SAW), was used to differentiate among different wines of the same variety of grapes which come from the same cellar. The electronic nose is based on eight surface acoustic wave sensors, one is a reference sensor and the others are coated by different polymers by spray coating technique. Data analysis was performed by two pattern recognition methods; principal component analysis (PCA) and probabilistic neuronal network (PNN). The results showed that electronic nose was able to identify the tested wines.

Detection of toxic gases by a tin oxide multisensor

A tin oxide multisensor with eight sensor elements has been utilized to detect different gases that are emitted from the chemical industry. The different sensors have been prepared using the RF reactive sputtering technique. Some components of this multisensor were doped with Pt and Cr by sputtering. Each sensor has been characterized by electrical measurements for detection of atmospheric pollution (nitrogen dioxide, carbon monoxide, toluene, and propanal). The detected gases are toxic and their extreme concentrations recommended in air oscillate from 1 ppm to hundreds of ppm. Detections were carried out with a single gas or a gas mixture (two gases) in dry air at 250/spl deg/C. The sensitivity and selectivity to these gases were studied. Backpropagation neural networks and their classification results were discussed.

Environmental applications of gas sensor arrays: combustion atmospheres and contaminated soils

Abstract Gas sensor arrays have been used to analyze volatile organic compounds in contaminated soils and exhaust gases coming from combustion processes. Sputtered thin films of semiconductor metal oxides were used as gas sensors in the sensor arrays. Combustion gases such as NOx, SO2 and benzene were detected in a highly toxic atmosphere formed by N2, O2, H2S, HF, HCl and water vapour. Sensitivities by 100% were obtained for different sensors when exposed to NOx and SO2. Six volatile organic compounds coming from contaminated soils were successfully identified using different pattern recognition methods such as principal component analysis and backpropagation neural networks. In both cases the use of the normalized fractional conductance change as preprocessing algorithm was decisive. Quantitative determinations of the mixtures of the volatile compounds were performed with relative prediction errors ranging from 2 to 50% for the calibration set. Higher errors were found using the validation data set. Backpropagation neural networks with partially connected hidden layer resulted in general more satisfactory than multiple linear regression methods because the response models were not well satisfied for all the sensors. The use of the normalized fractional conductance change as preprocessing algorithm gave the best results with the neural networks.

Activation of a vinyl carbon–hydrogen bond in a tris(pyrazolyl)boratoiridium complex. The X-ray crystal structure of [IrH{HB(pz)3}(σ-C8H13)(η2-C8H14)]

Reaction between [(Ir(µ-Cl)(C8H14)2}2](C8H14= cyclo-octene) and Na[ HB(pz)](pz = pyrazolyl) affords the vinyl hydrido complex [IrH{HB(pz)3}(σ-C8H13)(η2-C8H14)]. Protonation of this complex gives [IrH{HB(pz)3}(η2-C8H14)2]BF4. Treatment of [IrCl(C2H4)4] with Na[HB(pz)3] yields [Ir{HB(pz)3)(η2-C2H4)2]. The molecular structure of [IrH{HB(pz)3}(σ-C8H13)(η2-C8H14)](1) has been determined by X-ray analysis. Crystals of (1) are monoclinic, space group P21/n, with a= 20.284(2), b= 12.265(1), c= 20.554(2)A, β= 97.103(7)°, and Z= 8. The co-ordination around the iridium atom is distorted octahedral involving the three N atoms from the tris(pyrazolyl) borato on one side, and a hydride, a π-bonded cycle-octene, and a π-bonded cyclo-octenyl group on the other; the last three ligands are mutually cis.