Improving the Quality of European Hard Cheese by controlling interactions between Lactic Acid Bacteria and Propionic Acid Bacteria (LAB/PAB) (Stimulation of Propionic Acid Bacteria by Lactic

End of Project ReportTeagasc acknowledges with gratitude grant aid under the EU Framework Programme (FAIR 96-CT-1024).In the manufacture of Swiss-type cheese two successive fermentations occur. During manufacture, lactic acid bacteria (LAB), particularly Streptococcus thermophilus, Lactobacillus helveticus and Lb. delbrueckii subsp. lactis, convert lactose to lactate while, during ripening, propionic acid bacteria (PAB) convert lactate to propionic acid, acetic acid and carbon dioxide (CO2). CO2 is responsible for eye formation and propionic acid results in the typical nutty flavour of Swiss-type cheese. There have been a few reports of interactions between a small number of LAB and PAB but the compounds involved have not been identified. A better understanding of this phenomenon is necessary to select strains of PAB for cheesemaking and improve the quality of hard cheeses. Cheese cannot be used for such a study because of its complexity and the length of time it is ripened. Hence, a simple whey-based model developed by Piveteau et al (1995) was successfully used to study the interactions between LAB and PAB. In this procedure, the LAB were grown overnight in milk and the whey was collected by centrifugation. After neutralisation and filter-sterilisation, the growth of strains of PAB in this whey and in a control whey produced from the same milk by acidification with lactic acid were compared. The objectives of this study were to refine the model of Piveteau et al (1995) to study the interactions between LAB and PAB and to determine the nature of the stimulant(s) produced by the LAB. * Thirty-two combinations of different commercial strains of PAB and LAB were evaluated in a modified whey model. None showed any inhibition and all showed some degree of stimulation but the extent of the stimulation depended on the particular pair of PAB and LAB used. * An inhibitor of PAB was found in milk, which prevented the growth of PAB from low (105 cfu/ml) but not from high inocula (107 cfu/ml). The inhibitor was heat stable (to autoclaving for 15 min), of low molecular mass and could be removed by pre-growth of some but not all starter LAB in milk. * Growth of P. freudenreichii DPC 3801 in control whey was stimulated by peptone, tryptone, casein hydrolysed by the crude proteinase of Lb. helveticus DPC 4571 and by pre-growth of the lactobacillus in milk, but not by vitamins (riboflavin, thiamine, PABA, Ca panthothenate, biotin and nicotinic acid) or minerals (MgSO4, MnCl2, CoCl2 and CuSO4). * Growth of Lb. helveticus DPC 4571 in milk resulted in significant increases in peptide and amino acid production but the amino acids produced did not stimulate the growth of the PAB. Based on these results it was concluded that the stimulation was due to production of peptides by the LAB from casein. * The whey model developed by Piveteau et al (1995) to study the interactions between PAB and LAB was shown to be reproducible. Adjustment of the pH of the whey to 5.4 rather than 6.0, incubation at 24ºC rather than 30ºC and addition of 1% NaCl, to simulate cheese ripening conditions allowed growth of all the PAB tested. * Several chromatographic procedures, including ion-exchange, gel permeation and reverse-phase, high-pressure liquid chromatography failed to categorically identify the peptide(s) responsible for the stimulation of the PAB. In some of these chromatographic systems,the stimulatory activity was shown to be present in several peaks implying that different peptides were involved.European Unio

Thin films of calcium phosphate and titanium dioxide by a sol-gel route: a new method for coating medical implants

Titanium is a commonly used biomaterial for dental and orthopaedic applications. To increase its ability to bond with bone, some attempts were made to coat its surface with calcium phosphate (CaP). This paper describes a new type of coating. Instead of a pure CaP layer, a mixing of titanium dioxide (TiO2) and CaP is fabricated and deposited as a coating. These layers are deposited by a sol-gel route on pure titanium substrates using various pre-treatments. The method consists of mixing a solution of tetrabutyl ortho-titanate or a sol of titanium dioxide with a solution of calcium nitrate and phosphorous esters. This composite is deposited on to commercially pure titanium plates, mechanically polished or blasted with pure crystalline aluminum oxide, using the spin-coating technique. These coatings are then fired at 650 or 850°C for various times. The samples are characterized by X-ray diffraction for their crystallinity, X-ray photoelectron spectroscopy for their surface chemical composition and scanning electron microscopy for their topography. Samples treated at 850°C present a well-pronounced crystallinity, and a high chemical purity at the surface. The topography is strongly related to the viscosity of the precursor and the substrate pre-treatment. Possibilities to structure the outermost layer are presented. © 1999 Kluwer Academic Publisher

Quantum Hall effect anomaly and collective modes in the magnetic-field-induced spin-density-wave phases of quasi-one-dimensional conductors

We study the collective modes in the magnetic-field-induced spin-density-wave (FISDW) phases experimentally observed in organic conductors of the Bechgaard salts family. In phases that exhibit a sign reversal of the quantum Hall effect (Ribault anomaly), the coexistence of two spin-density waves gives rise to additional collective modes besides the Goldstone modes due to spontaneous translation and rotation symmetry breaking. These modes strongly affect the charge and spin response functions. We discuss some experimental consequences for the Bechgaard salts.Comment: Final version (LaTex, 8 pages, no figure), to be published in Europhys. Let

Influence of Enterococci and Thermophilic Starter Bacteria on Cheddar Cheese Flavour

End of Project ReportThis project set out to identify suitable enterococci and thermophilic starter strains which could be added to the cheese during manufacture (as starter adjuncts) with the specific aims of enhancing flavour during ripening as well as facilitating flavour diversity - a trait sought by many commercial Cheddar companies. This project confirmed the potential of thermophilic lactic acid strains to affect flavour when used as starter adjuncts in Cheddar cheese manufacture. Their use can also lead to the development of novel flavours. Many adjunct cultures proposed to-date to enhance Cheddar flavour are composed of strains of lactococcal starter, selected for their flavouring capacity. However, application of such strains in industry would lead to increased probability of phage attack on the primary starter. On the other hand, thermophilic lactic acid strains are phage unrelated to conventional starter and thus would not lead to the introduction of starter specific phage into the cheese plant. A thermophilic strain from the Moorepark collection (DPC 4571) was shown to have major commercial potential as a flavour enhancer.Department of Agriculture, Food and the Marin

Magneto-Roton Modes of the Ultra Quantum Crystal: Numerical Study

The Field Induced Spin Density Wave phases observed in quasi-one-dimensional conductors of the Bechgaard salts family under magnetic field exhibit both Spin Density Wave order and a Quantized Hall Effect, which may exhibit sign reversals. The original nature of the condensed phases is evidenced by the collective mode spectrum. Besides the Goldstone modes, a quasi periodic structure of Magneto-Roton modes, predicted to exist for a monotonic sequence of Hall Quantum numbers, is confirmed, and a second mode is shown to exist within the single particle gap. We present numerical estimates of the Magneto-Roton mode energies in a generic case of the monotonic sequence. The mass anisotropy of the collective mode is calculated. We show how differently the MR spectrum evolves with magnetic field at low and high fields. The collective mode spectrum should have specific features, in the sign reversed "Ribault Phase", as compared to modes of the majority sign phases. We investigate numerically the collective mode in the Ribault Phase.Comment: this paper incorporates material contained in a previous cond-mat preprint cond-mat/9709210, but cannot be described as a replaced version, because it contains a significant amount of new material dealing with the instability line and with the topic of Ribault Phases. It contains 13 figures (.ps files

Sign reversals of the Quantum Hall Effect in quasi-1D conductors

The sign reversals of the Quantum Hall Effect observed in quasi-one-dimensional conductors of the Bechgaard salts family are explained within the framework of the quantized nesting model. The sequence of reversals is driven by slight modifications of the geometry of the Fermi surface. It is explained why only even phases can have signign reversals and why negative phases are less stable than positive ones.Comment: 4 LaTex pages, 3 Postscript figure

Fully relativistic calculation of magnetic properties of Fe, Co and Ni adclusters on Ag(100)

We present first principles calculations of the magnetic moments and magnetic anisotropy energies of small Fe, Co and Ni clusters on top of a Ag(100) surface as well as the exchange-coupling energy between two single adatoms of Fe or Co on Ag(100). The calculations are performed fully relativistically using the embedding technique within the Korringa-Kohn-Rostoker method. The magnetic anisotropy and the exchange-coupling energies are calculated by means of the force theorem. In the case of adatoms and dimers of iron and cobalt we obtain enhanced spin moments and, especially, unusually large orbital moments, while for nickel our calculations predict a complete absence of magnetism. For larger clusters, the magnitudes of the local moments of the atoms in the center of the cluster are very close to those calculated for the corresponding monolayers. Similar to the orbital moments, the contributions of the individual atoms to the magnetic anisotropy energy strongly depend on the position, hence, on the local environment of a particular atom within a given cluster. We find strong ferromagnetic coupling between two neighboring Fe or Co atoms and a rapid, oscillatory decay of the exchange-coupling energy with increasing distance between these two adatoms.Comment: 8 pages, ReVTeX + 4 figures (Encapsulated Postscript), submitted to PR

Sign reversals of the quantum Hall effect and helicoidal magnetic-field-induced spin-density waves in quasi-one-dimensional organic conductors

We study the effect of umklapp scattering on the magnetic-field-induced spin-density-wave phases, which are experimentally observed in the quasi-one-dimensional organic conductors of the Bechgaard salts family. Within the framework of the quantized nesting model, we show that umklapp processes may naturally explain sign reversals of the quantum Hall effect (QHE) observed in these conductors. Moreover, umklapp scattering can change the polarization of the spin-density wave (SDW) from linear (sinusoidal SDW) to circular (helicoidal SDW). The QHE vanishes in the helicoidal phases, but a magnetoelectric effect appears. These two characteristic properties may be utilized to detect the magnetic-field-induced helicoidal SDW phases experimentally.Comment: 4 pages, latex, 3 figure

Effect of umklapp scattering on the magnetic-field-induced spin-density waves in quasi-one-dimensional organic conductors

We study the effect of umklapp scattering on the magnetic-field-induced spin-density-wave (FISDW) phases which are experimentally observed in the quasi-one-dimensional organic conductors of the Bechgaard salts family. Within the framework of the quantized nesting model, we show that the transition temperature is determined by a modified Stoner criterion which includes the effect of umklapp scattering. We determine the SDW polarization (linear or circular) by analyzing the Ginzburg-Landau expansion of the free energy. We also study how umklapp processes modify the quantum Hall effect (QHE) and the spectrum of the FISDW phases. We find that umklapp scattering stabilizes phases which exhibit a sign reversal of the QHE, as experimentally observed in the Bechgaard salts. These ``negative'' phases are characterized by the simultaneous existence of two SDWs with comparable amplitudes. As the umklapp scattering strength increases, they may become helicoidal (circularly polarized SDWs). The QHE vanishes in the helicoidal phases, but a magnetoelectric effect appears. These two characteristic properties may be utilized to detect the magnetic-field-induced helicoidal SDW phases experimentally.Comment: Revtex, 27 pages, 9 figure

Collective modes in a system with two spin-density waves: the `Ribault' phase of quasi-one-dimensional organic conductors

We study the long-wavelength collective modes in the magnetic-field-induced spin-density-wave (FISDW) phases experimentally observed in organic conductors of the Bechgaard salts family, focusing on phases that exhibit a sign reversal of the quantum Hall effect (Ribault anomaly). We have recently proposed that two SDW's coexist in the Ribault phase, as a result of Umklapp processes. When the latter are strong enough, the two SDW's become circularly polarized (helicoidal SDW's). In this paper, we study the collective modes which result from the presence of two SDW's. We find two Goldstone modes, an out-of-phase sliding mode and an in-phase spin-wave mode, and two gapped modes. The sliding Goldstone mode carries only a fraction of the total optical spectral weight, which is determined by the ratio of the amplitude of the two SDW's. In the helicoidal phase, all the spectral weight is pushed up above the SDW gap. We also point out similarities with phase modes in two-band or bilayer superconductors. We expect our conclusions to hold for generic two-SDW systems.Comment: Revised version, 25 pages, RevTex, 7 figure