Influence of different reactor types on Nannochloropsis oculata microalgae culture for lipids and fatty acid production

Greenhouse gases emitted into the atmosphere by burning of fossil fuels cause global warming. One option is obtaining biodiesel. Nannochloropsis oculata was cultured under different light intensities and reactors at 25°C for 21 days with f/2 medium to assess their effects on cell density, lipid, and fatty acids (FAs). N. oculata improved cell density on fed-batch glass tubular reactor (7 L) at 200 μmol E m⁻² s⁻¹, yielding 3.5 × 10⁸ cells ml⁻¹, followed by fed-batch Erlenmeyer flask (1 L) at 650 μmol E m⁻² s⁻¹ with 1.7 × 10⁸ cells ml⁻¹. The highest total lipid contents (% g lipid × g dry biomass⁻¹) were 44.4 ± 0.8% for the reactor (1 L) at 650 μmol E m⁻² s⁻¹ and 35.2 ± 0.2% for the tubular reactor (7 L) at 200 μmol E m⁻² s⁻¹, until twice as high compared with the control culture (Erlenmeyer flask 1 L, 80 μmol E m⁻² s⁻¹) with 21.2 ± 1%. Comparing the total lipid content at 200 μmol E m⁻² s⁻¹, tubular reactor (7 L) and reactor 1 L achieved 35.2 ± 0.2% and 28.3 ± 1%, respectively, indicating the effect of shape reactor. The FAs were affected by high light intensity, decreasing SFAs to 2.5%, and increased monounsaturated fatty acids + polyunsaturated fatty acids to 2.5%. PUFAs (20:5n-3) and (20:4n-3) were affected by reactor shape, decreasing by half in the tubular reactor. In the best culture, fed-batch tubular reactor (7 L) at 200 μmol E m⁻² s⁻¹ contains major FAs (16:0; 38.06 ± 0.16%), (16:1n-7; 30.74 ± 0.58%), and (18:1n-9; 17.15 ± 0.91%).     

Effect of selected yeast strains on the sensory properties of dry fermented sausages

This study examines the role of yeasts in the sensorial characteristics of dry fermented sausages. A total of 172 yeast strains were isolated from commercially obtained dry fermented sausages and their enzymatic activities studied. Those most active against meat proteins and pork fat were selected. Experimental sausages were manufactured and the yeasts inoculated onto the surface or into the mince. Control batches were manufactured similarly, but without inoculation. After ripening, the composition of the protein and lipid fractions were studied. The sensory properties of the products were evaluated by trained judges. Despite the enzymatic activity of the yeasts, the organoleptic characteristics of the sausages—irrespective of inoculation site—did not differ significantly from those of the controls. The influence of yeasts on the ripening of dry fermented sausages is, therefore, doubtful.     

Comparison of volatile components in raw and cooked green beans by GC-MS using dynamic headspace sampling and microwave desorption

 The effects of four culinary treatments (steaming and boiling in a covered pot, a pressure cooker or a microwave oven) on the volatile component profile of green beans were evaluated. Volatile compounds in raw and cooked beans were analysed by means of dynamic headspace sampling onto an adsorbent, followed by microwave desorption into a gas chromatograph equipped with a mass spectrometric detector. Twenty-seven compounds were identified, including alcohols, aldehydes, ketones, esters, terpenes, sulphur compounds and alkenes. All of the thermal treatments caused important changes in the volatile compound profile in particular an increase in carbonyl compounds and a decrease in alcohol compounds, most notably in the case of the covered pot. It is concluded that the change in aroma during the cooking of green beans depends on compounds from lipid oxidation as well as compounds from other types of reactions, for instance the Strecker degradation. Received: 8 March 1999 / Revised version: 23 April 1999     

The evaluation of scientific production: Towards a neutral impact factor

Measurement of research activity still remains a controversial question. The use of the impact factor from the Institute for Scientific Information (ISI) is quite widespread nowadays to carry out evaluations of all kinds; however, the calculation formula employed by ISI in order to construct its impact factors biases the results in favour of knowledge fields which are better represented in the sample, cite more in average and whose citations are concentrated in the early years of the articles. In the present work, we put forward a theoretical proposal regarding how aggregated normalization should be carried out with these biases, which allows comparing scientific production between fields, institutions and/or authors in a neutral manner. The technical complexity of such work, together with data limitations, lead us to propose some adjustments on the impact factor proposed by ISI which — although they do not completely solve the problem — reduce it and allow glimpsing the path towards more neutral evaluations. The proposal is empirically applied to three analysis levels: single journals, knowledge fields and the set of journals from the Journal Citation Report.     

Smooth sliding-mode observers for specific growth rate and substrate from biomass measurement

This paper addresses the estimation of specific growth rate and substrate concentration from biomass measurements in fermentation processes. Specifically, sliding-mode observers are proposed, for which finite-time global convergence is demonstrated using Lyapunov stability theory and concepts of variable structure systems. Two observers are developed for specific growth rate estimation, one producing a discontinuous estimation which is used afterwards for substrate estimation, and the other one – based on high-gain observers – that generates a smooth estimation with first-order dynamics and finite-time bounded convergence error. In the case of substrate estimation, an observer that increases the convergence rate to a vicinity of the real substrate concentration while achieving asymptotic convergence despite kinetic model uncertainties in properly excited processes is designed. This observer also exhibits first-order dynamics.     

Acidic Activated Carbons: An Efficient Catalyst for the Epoxide Ring-Opening Reaction with Ethanol

The epoxides (styrene oxide and 1,2-epoxyhexane) reaction with ethanol was carried out, catalysed with acidic activated carbons. The reactions were carried out under microwave irradiation. In the 1,2-epoxyhexane reaction, high yields were attained in some of the reaction conditions tested, although the regioselectivity was not high. For the styrene oxide reaction, the conversion was higher and the regioselectivity was high in most cases. For comparison, the reactions have been also performed in a batch reactor system under thermal activation.