Roland Verhé

Total and individual carotenoids and phenolic acids content in fresh, refrigerated and processed spinach (Spinacia oleracea L.).

The carotenoid and phenolic acid contents in fresh, stored and processed (blanched, frozen and boiled) spinach were comparatively determined by spectrophotometric and HPLC analyses. The major carotenoids identified after HPLC analysis in saponified samples were lutein (37-53μg/kg), β-carotene (18-31μg/kg), violaxanthin (9-23μg/kg) and neoxanthin (10-22μg/kg). These carotenoids were all affected by storage and/or heating. The content of carotenoids was best preserved after storage for one day at 4°C. The total phenolic content in the fresh spinach was 2088mg GAE/kg FW. After LC-MS analysis three phenolic acids were identified and quantified. These being ortho-coumaric acid (28-60mg/kg FW), ferulic acid (10-35mg/kg) and para-coumaric acid (1-30mg/kg) depending on the sample type. After storage of spinach at different temperatures (4°C or -18°C) the amount of total phenolic compounds decreased by around 20%, while the amount of individual phenolic acids increased by four times on average.

Analysis of volatiles of malt whisky by solid-phase microextraction and stir bar sorptive extraction

Blended Scotch whisky was analysed by solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE) to study the composition of the volatiles. For SPME analysis, three different fibres were compared, poly(dimethylsiloxane) (PDMS) (100 microm). poly(acrylate) (PA) (85 microm) and divinylbenzene-Carboxen on poly(dimethylsiloxane) (DVB-CAR-(PDMS) (50/30 microm). It was found that the PDMS and DVB-CAR-PDMS fibres showed a higher enrichment capacity than PA as well as a better reproducibility. The influence of sampling time, temperature and salt addition on the enrichment of volatiles as well as the difference between liquid and headspace SPME were studied. An optimum SPME method was developed. Finally a more recent sample preparation technique, namely SBSE was evaluated to extract whisky volatiles.

Flavour analysis of Greek white wine by solid-phase microextraction-capillary gas chromatography-mass spectrometry.

Solid-phase microextraction (SPME) was optimised for the qualitative determination of the volatile flavour compounds responsible for the aroma of Greek Boutari wine. Several factors influencing the equilibrium of the aroma compounds between the sample and the SPME fiber were taken into account, including the extraction time, the extraction temperature, the sampling mode (headspace and direct immersion or liquid SPME), and the presence of salt. Four different SPME fibers were used in this study. namely poly(dimethylsiloxane) (PDMS), poly(acrylate), carbowax-divinylbenzene and divinylbenzene-carboxen on poly(dimethylsiloxane). The best results were obtained using the PDMS fiber during headspace extraction at 25 degrees C for 30 min after saturating the samples with salt. The optimised SPME method was then applied to investigate the qualitative aroma composition of three other Greek wines, namely Zitsa, Limnos and Filoni.

Heat resistance of Bacillus cereus emetic toxin, cereulide

Aims:  The study describes the effects of heating temperature and exposure time on the thermal stability of cereulide under different conditions (pH, presence/absence of oil phase and cereulide concentration).

Chemical and physical transitions of periodate oxidized potato starch in water

Abstract Physical and chemical transitions of dialdehyde starch in aqueous suspensions have been determined as a function of temperature and pH. The pH conditions were restricted to neutral or lower, since alkaline degradation is commonly recognized. Physical alterations were determined by measuring viscosity transitions at room temperature and upon heating. Chemical degradation was surveyed by controlling the amount of aldehydes, the production of carboxylic acids and the decrease in molecular weight. At neutral conditions and upon heating at 90 °C extensive chemical degradation occurred. This was manifested by a gradual conversion of aldehydes into carboxylic acids and alcohols, accompanied by a decrease in molecular weight. Degradation upon heating was minimized by reducing the pH to 3. At ambient temperature, the granular integrity was lost beyond pH 5 or 6 depending on the degree of oxidation of the material.

Modeling of alpha-tocopherol loss and oxidation products formed during thermoxidation in triolein and tripalmitin mixtures.

The degradation of α-tocopherol and the formation of α-tocopherol and triacylglycerol oxidation products at high temperatures (150–250°C) over a heating period (0–4h) for a model system ranging between triolein and tripalmitin were modeled by use of an experimental design. The oxidation products of α-tocopherol formed under these conditions were α-tocopherolquinone (1.4–7.7%) and epoxy-α-tocopherolquinones (4.3–34.8%). The results indicate a very high susceptibility of α-tocopherol to capture peroxyl radicals upon oxidation, leading to the formation of polar tocopherol oxidation products. Both α-tocopherolquinone and epoxy-α-tocopherolquinones were not stable upon prolonged heating and were further degraded to other unknown oxidation products. The kinetics of α-tocopherol oxidation were significantly influenced by the triolein/tripalmitin ratio. By increasing the level of triacylglycerol unsaturation the rate of α-tocopherol recovery after heating increased significantly from 2.2 to 44.2% whereas in the meantime triacylglycerol polymerization increased from 0 to 3.7%.

Reactivity of α-chloro-aldimines☆

Abstract A series of secondary N-1-(2-chloroalkylidene)amines has been prepared by condensation of disubstituted acetaldehydes with primary amines followed by chlorination with N-chlorosuccinimide in carbontetrachloride. A study of the reactivity of these N-homologues of α-chloroaldehydes is described. Treatment of the title compounds with sodium methoxide in methanol gave high yields of α,β-unsaturated aldimines. However, N-1-(2-chloro-2-methylpropylidene)amines afforded a mixture of elimination and rearrangement products, which proceeded via an aziridine intermediate. On the other hand, α-phenyl-substituted α-chloro aldimines on treatment with methoxide in methanol underwent α-substitution, consistent with an S N 1 mechanism. Powerful nucleophiles such as sodium thiophenolate in methanol and sodium azide in acetone caused α-substitution. Reaction of α-chloro aldimines with Grignard reagents produced coupling of two aldimine units or α-alkylation. Finally the reactivity of α-chloro aldimines was compared with the reactivity of the corresponding oxygen-analogues, i.e. α-chloro aldehydes.

Effect of rosemary extract dose on lipid oxidation, colour stability and antioxidant concentrations, in reduced nitrite liver pâtés

The oxidative stability of liver pâté was investigated in relation to different doses of rosemary extract (RE) and sodium nitrite. Colour stability, lipid oxidation (TBARS) and concentrations of ascorbic acid, α-tocopherol, carnosic acid and nitrite were measured on the batters before cooking and on the cooked liver pâté before and after exposure to light and air for 48 h at 4°C. Results showed that the use of RE significantly reduced lipid oxidation, whereas it had no effect on colour stability. Ascorbic acid and nitrite concentrations were significantly higher and lower respectively when RE was added. RE dose-dependently increased the concentration of carnosic acid. Lower sodium nitrite doses resulted in significantly lower nitrite concentrations and slightly lower TBARS values. It was concluded that in liver pâté sodium nitrite levels may be lowered to 80 mg/kg without negatively affecting colour and lipid stability and that the use of RE may help in maintaining lipid stability.

A Facile Synthesis of 1,2-Disubstituted Aziridines

Abstract In spite of the fact that a number of methods are available for the preparation of aziridines, general synthetic routes leading to 1,2-disubstituted aziridines remained laborious in most cases(2-6). A convenient and versatile synthesis is desirable in order to permit studies of this important biologically active heterocyclic system.

The gelation of dialdehyde starch

The rheological behaviour of periodate oxidized potato starches has been investigated in both dilute and concentrated aqueous dispersions. On heating, low viscosity solutions were obtained at low concentrations and viscoelastic gels at high concentrations. During the gelation process, two types of gel structure were distinguished. First a particle gel is formed, and on continued heating and shearing, deformation and disruption of the granules is observed, resulting in the formation of a polymer network. The increasing stability of the particle gels with increasing degree of oxidation has been attributed to an increase in particle rigidity. The aldehyde groups in dialdehyde starch are supposed to reinforce the granular structures, as a result of intragranular hemiacetalization. The gel stability could be improved by adding native potato starch to the premix.