Volatile fraction and sensory characteristics of Manchego cheese. 2. Seasonal variation

An automatic purge and trap apparatus, coupled to a GC-MS was used to study the seasonal variability of the volatile fraction of raw milk Manchego cheese. Both season and dairy significantly affected abundance of most volatile compounds. Most aldehydes, methyl ketones, n-alcohols, and secondary alcohols reached significantly higher concentrations in spring cheeses. Branched chain alcohols showed significantly higher concentrations in autumn and winter cheeses, while significantly higher amounts of diketones were found in summer cheeses. Most ethyl esters reached higher concentrations in spring and winter cheeses and lower in autumn cheeses. Lower concentrations of alpha-pinene were found in spring cheeses, and higher amounts of limonene were observed in winter cheeses. Heptane and octane were significantly more abundant in summer cheeses. No significant seasonal differences were found either for quality or intensity scores.     

Quantification of significant volatile components of pacharán

 Pacharán is a traditional drink from Navarra (Spain). This liqueur is obtained by maceration of sloe berries (Prunus spinosa L.) with aqueous ethanol and subsequent addition of sugar and essential oils of anise (Pimpinella anisum L. or Illicium verum H.). The following volatile components of pacharán were identified and quantified: cis-anethol; trans-anethol; anisaldehyde; benzaldehyde; benzyl alcohol; γ-butyrolactone; 1,1-diethoxyethane; ethyl benzoate; ethyl lactate; diethyl malate (hydroxybutanedioic acid diethyl ester); estragol (methyl chavicol); eugenol [2-methoxy-4-(2-propenyl)-phenol]; 2-furaldehyde; linalool; cis-3-hexen-1-ol; (4-methoxyphenyl)propanone; 2-phenylethanol and vanillin. Received: 3 November 1997 / Revised version: 29 December 1997     

Volatile compounds in fresh meats subjected to high pressure processing: Effect of the packaging material

The effect of high pressure treatment (400MPa, 10min at 12°C) on the volatile profile of minced beef and chicken breast, packaged with or without aluminum foil in a multilayer polymeric bag, was investigated. The analysis of the volatile fraction was carried out by dynamic headspace extraction coupled to gas chromatography-mass spectrometry. Pressurization produced significant changes in the levels of some volatile compounds presumably coming from microbial activity. Some alcohols and aldehydes decreased, while other compounds, such as 2,3-butanedione and 2-butanone, were more abundant in high pressure processed meats. A significant migration of compounds from the plastic material was observed, mainly branched-chain alkanes and benzene compounds. Two functions built by the principal component analysis explained a high percentage of the variance and could be used to separate the samples into four distinct groups, according to high pressure treatment and packaging material.     

A study on the importance of colour in pacharán

 Pacharán is a traditional drink of Navarra (Spain). This liqueur is an alcoholic drink which ranges from intense pink to red in colour and is based on sloe (Prunus spinosa, L.), essential oils of aniseed, and sugar. A sensory analysis was performed using samples from 21 different brands of commercial pacharán. Stepwise regression was employed to identify the physicochemical parameters responsible for the sensory attributes of colour, visual intensity of colour, and overall impression. The physicochemical variables which best predicted the sensorial attribute colour were colour intensity and titratable acidity. For the visual intensity of colour, key indicators were colour intensity, titratable acidity and hue, the last-mentioned variable having a negative effect. With respect to the overall impression, pH, ethanol content and colour intensity correlated to quality. Received: 12 February 1998 / Revised version: 13 May 1998     

Effect of a food-grade enzyme preparation fromAspergillus oryzae on free fatty acid release in Manchego-type cheese from ovine and bovine milk

The addition of 50 mg Flavor Age (blend of lipase, proteinases and peptidases fromAspergillus oryzae) per kilogram of mixed ovine plus bovine milk for the manufacture of Manchego-type cheese caused the release of abundant free fatty acids (FFA), especially the short-chain fatty acids (C₄ to C₁₀). The effect accentuated with ripening time, the cheeses reaching a level of FFA around 2% at 120 days. The high concentration of FFA could have partially inhibited the growth of starter culture, as can be deduced from the higher residual lactose content of enzyme-treated cheeses. The results are compared and related to those obtained in a previous study on proteolysis and flavour development by the same enzyme preparation. They suggest that in the case of Man-chego-type cheese the liberation of FFA, although necessary, could be less important for flavour enhancement than the production of free amino acids.     

Biodegradable Polycaprolactone-Titania Nanocomposites: Preparation,Characterization and Antimicrobial Properties

Nanocomposites obtained from the incorporation of synthesized TiO₂ nanoparticles (≈10 nm average primary particle size) in different amounts, ranging from 0.5 to 5 wt.%, into a biodegradable polycaprolactone matrix are achieved via a straightforward and commercial melting processing. The resulting nanocomposites have been structurally and thermally characterized by transmission electron microscopy (TEM), wide/small angle X-ray diffraction (WAXS/SAXS, respectively) and differential scanning calorimetry (DSC). TEM evaluation provides evidence of an excellent nanometric dispersion of the oxide component in the polymeric matrix, with aggregates having an average size well below 100 nm. Presence of these TiO₂ nanoparticles induces a nucleant effect during polymer crystallization. Moreover, the antimicrobial activity of nanocomposites has been tested using both UV and visible light against Gram-negative Escherichia coli bacteria and Gram-positive Staphylococcus aureus. The bactericidal behavior has been explained through the analysis of the material optical properties, with a key role played by the creation of new electronic states within the polymer-based nanocomposites.     

Densification of silicon nitride powder by spark plasma extrusion

The simultaneous extrusion and sintering of ceramic materials using the spark plasma extrusion (SPE) technique is an alternative densification route for the powders examined in this study. SPE with Y₂O₃ and Al₂O₃ as the additives was employed for the concurrent densification and extrusion of pure α-Si₃N₄ commercial powder. Three compositions of α-Si₃N₄ powders, namely SN-4, SN-12, and SN-20, were studied to understand the effect of additives on the sinter-extrusion process. The number in the mixture name corresponded to the weight percentage of additives in the samples. A mechanical shaker was used to thoroughly mix the selected powder compositions in isopropanol for 24 h at 720 rpm. It was then dried in a furnace at 100 °C for 3 h. The sinter-extrusion treatment was conducted for a holding time of 5 min at a heating rate of 300 °C/min and a sintering temperature of 1500 °C with a pressure in the range of 12–63 MPa. The maximum degree of extrusion was attained when the total amount of additives was at 20 wt% (SN-20 series). As the total amount of additives increased, the capillary pressure gradients led to an inhomogeneous liquid distribution throughout the specimen, which in turn promoted further densification of the Si₃N₄ ceramics. Owing to the conical geometry of the graphite die used for the extrusion process in this study, the largest densification values observed in the extruded ceramics corresponded to the base and the middle sections of the SN-20 series (relative density ~92%). The latter could only take place once the α-to β-Si₃N₄ phase transformation occurred, leading to significant shrinkage of the material.     

Growth and Characterization of TCNQ-Doped Ni(II)TAAB Thin Film As a New π-Conjugated Organic Semiconductor

Semiconductors - The aim of this work was to obtain a π-conjugated organic semiconductor with the macrocycle Ni(II)(TAAB) ([tetrabenzo (b, f, j, n) [1,5,9,13]tetraazacyclohexadecine]Ni(II) and...