Kinetics of xanthan gum production from whey by constructed strains of Xanthomonas campestris in batch fermentations

Two new constructed strains of X. campestris XLM1521 and XMT1, either alone or in mixed cultures were used for the production of xanthan gum in batch fermentations from whey. Fermentations were carried out at three different pH levels of 6.0, 7.0 and 8.0 and the results were compared with those previously reported for fermentations in Erlenmeyer flasks without controlling the pH. The kinetics of cultures of the strain X. campestris XLM1521 were studied in a batch reactor at constant pH values. A mathematical model, based on the Luedeking-Piret equation, was used and experimental design was employed in order to correlate model's parameters with pH variation. The highest xanthan gum concentration, 17.3 g/l, was observed at pH 8.0. This is the largest amount of xanthan gum reported so far.     

Robust sliding-mode control applied to a 5-link biped robot

In this paper the application of robust control to a 5-link biped robotic model is investigated through the sliding mode approach, and compared to pure computed torque control. The biped consists of five links, namely the torso and two links in each leg. These links are connected via four (two hip and two knee) rotating joints which are considered to be friction-free and driven by independent d.c. motors. The locomotion of the biped is assumed to be constrained on the sagittal plane. The paper provides a full derivation of the biped dynamic model (single-leg support phase, biped-in-the-air phase) and an outline of the computed torque and sliding mode control algorithms. The simulation results were derived with two sets of parameters (one of which corresponds to a human-sized biped) and several degrees of parametric uncertainty (from 10% to 200%). In all cases the results obtained through the sliding mode control were much better than those obtained with the computed torque control. This superiority was shown to become stronger as the degree of uncertainty and the size of the biped increases.     

Comparative mutagenicity studies on fried minced beef,grilled sausage and grilled hamburgers

The mutagenicity of the basic fractions of fried beef patties, grilled hamburgers and grilled sausages was determined in the Ames test using activation systems (S9-mix) derived from untreated and Aroclor-pretreated rats and hamsters, and from rats pretreated with 3-methylcholanthrene or phenobarbitone. In order to indicate whether the mutagenic activity was due to the presence of thermally generated amino imidazo aza-arenes of the type previously identified in heated meat products (i.e. 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo-[4,5-f]quinoline (MeIQ) and 2-amino-3,8-dimethylimidazo[4,5-f]quin-oxaline), these compounds were assayed under the same conditions. The mutagenicity of the basic fractions of the cooked foods and of the three aza-arenes varied with the activation system used. The activation patterns of the basic fractions from fried beef and grilled sausages resembled that of IQ, whereas that of grilled hamburgers was more similar to that of MeIQ. Interestingly the total mutagenic activity of fried beef patties was greater than that of grilled hamburgers.