The effects of freezing and frozen storage of ewe's milk cheese on the viability and proteolytic activity of lactococci used as a starter

A study has been conducted on the effect of two freezing conditions (slow and fast) and frozen storage of ewe's milk cheese (?20 °C for 4 months) on the viability and the proteolytic (cascinolytic and aminopeptidase) activity ofLactococcus lactis subsp.lactis andL. lactis subsp.cremoris used as starters in the manufacture of cheese. The study was carried out on the lactococci subjected to freezing and frozen storage, either in the cheeses or in curds simulating a model system. As well as other parameters used to quantity microbial activity, the total viable counts during the subsequent cheese ripening have been analysed in the frozen cheeses. Frozen storage of the investigated lactococci, either in the cheese or in model systems, gave rise to significant decreases in the caseinolytic and aminopeptidase activities greater than did freezing alone. No clear differences were found in enzymatic activity values when using slow or fast freezing conditions. Storage of the cheeses under frozen conditions also affected microbial viability and consequently caused a greater decrease of the viable flora during subsequent ripening of the frozen stored cheeses.     

Plasma-induced polymerization

Summary Preliminary results on plasma-induced bulk homopolymerization of styrene, acrylic acid, methacrylic acid, ethyl acrylate and on plasma-induced solution homopolymerization of N-vinyl carbazole, styrene and acrylamide are presented. Experimental data suggest that a radical mechanism of polymerization has to be considered to explain this new approach to polymer synthesis.     

Global interinsic kinetics of wood oxidation

Weight loss curves of two wood species (beech and Douglas fir) have been measured in air for four heating rates between 5-40 K/min and a final temperature of 873 K. A four-step series mechanism describes well the details of the thermogravimetric curves of the devolatilization/combustion process. The rates of the first three reactions are linear in the solid mass fraction and the activation energies are 106, 226 and 114 kJ/mol, respectively. The fourth step presents a power-law dependence (n=1.54) on the solid mass fraction and an activation energy of 183 kJ/mol. Pre-exponential factors and stoichiometric coefficients take into account the differences between the two wood species.     

Morphology and surface properties of side-chain modified polysulfones

Two series of modified polysulfones containing siloxane-aliphatic pendant moieties were analysed by optical microscopy, transmission electron microscopy, electron diffraction, contact angles measurements and X-ray photoelectron spectroscopy (XPS or ESCA), in order to establish the microstructure and surface properties. All samples exhibited biphasic bulk morphology due to a crystallization tendency induced by the pendant moiety, and silicon enriched surface irrespective of the substitution degree. The values of the surface tension calculated from contact angle measurements were in agreement with the hypothesis of surface enrichment.     

A system analysis of technological changes in the Romanian high voltage power network

Increasing demand for energy requires large-scale construction of power plants and adequate growth of the transmission network. Currently, several high-voltage transmission subsystems (110, 220, 400, 500, and 750 kV) coexist in the same network. We investigate the mechanism of substitution of voltage for the medium-size energy system in Romania by using the Marchetti-Nakicenovic model and Romanian data of the period 1965–1981. The horizon of our prediction is up to the year 2030.     

Optimization of the heterogeneous Fenton-oxidation of the model pollutant 2,4-xylidine using the optimal experimental design methodology

Among advanced oxidation processes (AOP), the photochemically enhanced Fenton reaction (photo-Fenton) may be particularly effective for the treatment of industrial waste water, and the possibility to use solar light is an additional advantage of this process. In the present work, a Fe³⁺-exchanged zeolite Y was tested as a heterogeneous photo-Fenton catalyst for the degradation of the model organic pollutant, 2,4-xylidine. The performance of the catalyst was investigated using a bench photochemical reactor as well as solar reactors. The incident solar radiant powers (determined by ferrioxalate actinometry) showed linear correlations with the outputs of a Si-photodiode and a bolometer mounted on the solar unit, and could therefore be easily estimated from the on-line observation of the sensor outputs. The experimental design methodology was used for planning the experiments under normalized conditions and for modeling the rates of 2,4-xylidine oxidation as a function of the concentrations of the additives (Fe³⁺-exchanged zeolite catalyst and hydrogen peroxide). Although a direct quantitative comparison between both reactors is difficult (different geometries and volumes, different spectral distribution of the radiation sources), the performance of the solar reactor appears to compare favorably with that of the bench photochemical reactor.     

Integral Evaluation for Hydrotreating Catalyst Activity

A procedure for the evaluation of activity for industrial hydrotreating catalysts is described in detail. The evaluation of the catalyst quality and its performance is carried out on different experimental levels. The first corresponds to the analytic characterization of physical and chemical properties of the catalyst. Levels 2 and 3 correspond to the evaluation of its catalytic properties in a micro reactor and pilot plant, respectively. A comparison of the experimental results with those calculated using mathematical models constitutes the next evaluating level. With all these results we can have a preliminary diagnosis of the catalyst's quality. If data from the operation of the catalyst at industrial plant are available, it is possible to make a comparison with those obtained in the different experimental levels. With all of this information it is also possible to make performance predictions in terms of activity, selectivity, and stability. The obtained results are very consistent at different levels of evaluation and allow us to establish the quality of the catalyst with great confidence.     

Wettability of glass substrates by molten nylon-6

A study of the adhesion of molten nylon-6 to glass, vitreous silica and dehydrated silica is performed by the sessile drop method at 243°C. The influence of polymerization conditions, nature of substrate, thermal pretreatment of the polymer and lithium chloride addition on wettability is examined. The most relevant results show that thermal pretreatment of the polymer is a determining step in wettability and that LiCl addition causes an increase of contact angle, as a consequence of the decrease in the substrate-molten polymer interactions. The results are interpreted by means of an interfacial model based on additive polar and dispersion forces.     

Characterization of eutectic mixtures in different natural fat blends by thermal analysis

Samples of cacao butter (CB), mango seed almond fat (Mangifera indica var. Manila) (MAF), and zapote mamey seed almond fat (Pouteria sapota) (ZMAF), were analyzed for their fatty acid composition and were mixed according to a 3‐factor simplex‐lattice design. Mixtures were stabilized, their fusion and crystallization thermal behavior, and solid fat contents were evaluated using differential scanning calorimetry. Ternary phase behavior was analyzed with isosolid diagrams. Results showed that the main fatty acids in the fats were oleic, stearic, and palmitic acids: CB: 31.1, 35.5, and 27.8%; MAF: 37.5, 42.6 and 9.9%, and ZMAF: 50.0, 27.2 and 12.0%, respectively. Fusion behavior showed a single curve with only one maximum and one small shoulder for CB and MAF, and three maximum points for ZMAF. Crystallization was also a single curve with only one maximum for the three fats. Solid fat contents at 21.1 °C were: CB: 87.5; MAF: 68.5 and ZMAF: 6.6%. Ternary phase behavior showed that these fats can support preparation of mixtures with different compositions that could become equivalent to cocoa butter for use in alimentary, pharmaceutical, and cosmetic industries.     

Iberian ham headspace: odorants of intermuscular fat and differences with lean

The odorants from the intermuscular fat of Iberian ham were characterised for the first time and compared with those of the lean. A headspace extraction method and gas chromatography–olfactometry based on the detection frequency method were used. Compounds contributing to intermuscular fat odour were aldehydes (9), ketones (3), esters (2), nitrogen‐containing compounds (2), and one alcohol (1‐octen‐3‐ol). Eight odorants were identified for the first time as constituents of dry‐cured ham fat. The most potent odorants were hexanal and (Z)‐3‐hexenal, 3‐methylbutanal, 1‐octen‐3‐one and 1‐octen‐3‐ol and 2‐methylpropanal. Significant differences with odorants from the lean of the same hams were found; the largest differences appeared in sulfur‐containing compounds (specifically hydrogen sulfide, methanethiol and 2‐methyl‐3‐furanthiol), which seem not to contribute to fat odour but are some of the most potent odorants of lean. Significant and large differences were also found for other compounds such as 1‐octen‐3‐one and 1‐octen‐3‐ol, ethyl 2‐methylpropanoate, 2‐pentanone and 2,3‐butanedione. Copyright © 2004 Society of Chemical Industry