MODELISATION PRINCIPLES FOR DRYING OF GELS

ABSTRACT

When one wants to understand and model the drying of high water content gels, one needs to gather all thermal physical parameters and to derive a physical model based on independently measured parameters. We chose to work experimentally and theoretically on water diffusion and drying of spheres of polyacrylamide gel.

We have demonstrated the strong influence of vitreous transition on the relationship of water diffusivity with moisture content. Values of the diffusion coefficient and temperature shift factor for diffusion have been proposed.

Convective and micro-wave drying kinetics show the presence of a drying phase purely specific to radiation absorption. Finally, we have proposed a mathematical model containing independent physical parameters, which' not only predicts mass fluxes but also analyses critical physical phenomena.     

High resolution two-dimensional electrophoresis as a tool to differentiate wild from farmed cod (Gadus morhua) and to assess the protein composition of klipfish

Tris and CHAPS–urea extracts from wild and farmed cod muscle and from rehydrated cod klipfish fillets were analyzed by one (1DE) and two-dimensional electrophoresis (2DE). 2DE maps of tris extracts from farmed cod differed from the wild in a series of spots of Mw 35 and 45 kDa. The CHAPS–urea extracts from farmed cod had a several spots of Mw between 100 and 45 kDa, which were hardly detectable in wild cod and very prominent in klipfish. Klipfish was clearly different from the other samples: the myosin heavy chain was hardly detectable in these samples, and the tris extracts contained fewer, and the CHAPS–urea more spots than the corresponding extracts from the raw muscles. Further identification of these potentially diagnostic spots will make it easier the differentiation of farmed from wild cod and the evaluation of klipfish processing on the protein content of the product.     

Electroless cobalt deposition from a glycinate solution using morpholine borane as a reducing agent

Electroless cobalt films were deposited from a neutral pH glycinate solution without additives using morpholine borane (MB) as a reducing agent. The rate of deposition rises with increase in concentration of solution components (Co ions, MB and glycine), and pH. The efficiency of cobalt discharge increases when the deposition is performed from the Co(II) complex with glycine. XPS data indicate that boron and oxygen are incorporated into the cobalt films. Two forms of boron (elemental and its oxide) were detected in the electrolessly deposited cobalt films.     

The Role of Cu(I) in the Process of Forming Cu2–xS Coatings by a Chemical Route

The interaction of the Cu₂O adsorbed with Na₂S_n (n = 1–4), during formation of the Cu_2–xS coatings has been investigated by cyclic voltammetry.

The summarized reaction of this process has been shown to correspond to the equation:

Na₂S_n + Cu₂O_ad + H₂0 → Cu₂S_ad + (n–1)S^o + 2NaOH,

where S^o/Cu=(n–1)/2. Such a stoichiometry of reaction can be explained by the formation of an intermediate—the adsorbed polysulphide of Cu(I)—and by its subsequent decomposition into Cu₂S and S^o.

When a thicker coating is being formed, i.e., when the surface being coated is repeatedly immersed into an ammoniate solution of Cu(I) and S^o fully bounded:

S^o_ad + 2 Cu⁺ → CuS + Cu²⁺.

At the same time due to different solubility products (L=2.5·10^?48 and 6.3·10^?36 for Cu₂S and CuS respectively), an exchange

CuS_ad + 2(1–x)Cu⁺ → Cu_2–xS_ad+ (1–x)Cu²+ occurs.

After formation of Cu²⁺, parallel processes characteristic for the interaction of Cu(II) with Na₂S_n start to take place, during which S^o is also formed.     

Dynamic pricing of wind futures

Daily average wind speeds are dynamically modelled by a continuous-time autoregressive model with seasonal mean and volatility. Futures prices based on an index of aggregated wind speeds are derived, and it is shown that the Samuelson effect breaks down. The volatility of these futures will decrease when approaching maturity, an effect which is explained by the memory in higher-order autoregressive models.     

Interactions between flavour release and rheological properties in model custard desserts: Effect of starch concentration and milk fat

The influence of the concentration of various reagents and of the storage time on the flavour release of custard desserts was evaluated by headspace solid-phase microextraction and supported by rheological measurements. The presence of milk fat induced a significant decrease of the headspace concentration of flavour compounds, mainly due to hydrophobic matrix–flavour interactions. An elevated starch concentration enhanced the strength of the custard gels considerably. However, the increasing starch concentration resulted in an increased flavour release at low flavour concentrations, while a tendency to flavour retention was noted at higher flavour concentrations. During storage time, a denser network was formed as shown by rheological measurements, but no significant difference in flavour release was noted upon storage (three days). These results show that the complex interactions between flavour compounds and the food matrix in a model custard are difficult to predict and have to be carefully evaluated by a combination of rheological parameters and physicochemical interactions.