Ildefonso Caro

Alkaline and alkaline peroxide pretreatments at mild temperature to enhance enzymatic hydrolysis of rice hulls and straw.

The current study explores alkaline and alkaline peroxide pretreatments in order to achieve a method to improve saccharification of agricultural residues for ethanol production. The effects of reagent concentration and pretreatment time at 30°C and atmospheric pressure on biomass dissolution after the pretreatment and enzymatic hydrolysis of the pretreated biomass were investigated. In fact, although all pretreatments tested improved enzymatic hydrolysis of native residues, the best results were not achieved for the highest biomass loss. The maximum conversions to reducing sugars in the hydrolysis stage of 77.5% and 92.6% were obtained for rice hulls and straw pretreated by alkaline peroxide (4%, 24h) and alkaline (1%, 48 h) methods, respectively. For both pretreated residues, the reduction to more than half the recommended enzyme loading allowed obtaining more than 94% the reducing sugars attained with the recommended dose.

Xylanase production by Aspergillus awamori under solid state fermentation conditions on tomato pomace

Inthiswork,� tomatopomace,� awasteabundantlyava ilableintheMediterraneanandothertemperate� climatesagrofoodindustries,�hasbeenusedasraw �materialfortheproductionofsomehydrolyticenz ymes,� includingxylanase,�exopolygalacturonase�(exoPG), �cellulase�(CMCase)�and�α�amylase.�Theprincipalst ep� oftheprocessisthesolidstatefermentation�(SSF )�ofthisresiduebyAspergillus awamori.�Inseveral� laboratoryexperiments,�maximumxylanaseandexoPG �activitiesweremeasuredduringthefirstdaysof�

Comparative study of alcohol dehydrogenase activity in flor yeast extracts

The highest activities of alcohol dehydrogenase were obtained when flor yeasts were grown on L-lactic acid as the main carbon source. The strains with the lowest average of alcohol dehydrogenase activities, grown on glucose and ethanol, make up the velum on wines during the early stages ageing. One of the strains studied ( Saccharomyces cerevisiae, M10) may be a suitable source from which to isolate this enzyme (32 units of activity per mg protein).

Comparative study of crossflow microfiltration with conventional filtration of sherry wines

Abstract The present work reports, firstly, on the application of the gel-polarisation model to the crossflow microfiltration of sherry wines and brandies, in order to calculate the model parameters. In a preliminary set of experiments, the influence of the transmembrane pressure (TP) on the filtrate flow was studied, at several feed flows. The obtained results show a constant ratio between the optimum TP (TPopt) and the feed flow of 32×10 −4 l h −1 Pa with a TPopt of 11×104 Pa, for a feed flow of 360 l h −1 for all products. The obtained values of D for the different products can indicate that the average size of the particles in the gel layer is from 10 to 50 nm. Secondly, it has compared crossflow microfiltration process with classic filtration processes, which are used in the standard production system. The results show that the microfiltration has a higher effectiveness than conventional filtration, except in the case of brandy, where conventional filtration is more effective.

A kinetic model for growth of Acetobacter aceti in submerged culture

Abstract This paper proposes a kinetic model for growth, in low alcohol media, of Acetobacter aceti in submerged culture. The model combines the influence of substrate (ethanol) concentration, product (acetic acid) concentration and dissolved oxygen on the specific microorganism growth rate. Experimental data were obtained, both in the laboratory and industrially, using a variety of discontinuous fermentation apparatus with automatic control, and either open or closed gas recirculation systems. The operation conditions applied were those typical of acetic fermentation processes in the food industry. Examination of the results obtained makes it possible to determine the characteristic influence of each of the variables indicated, and to calculate the values of the different parameters of the proposed growth equation.

Kinetic equation for growth of Thiobacillus ferrooxidans in submerged culture over aqueous ferrous sulphate solutions

Abstract This paper proposes a useful equation for ferrous sulphate oxidation processes by Thiobacillus ferrooxidans in batch operations. It is based on the equation proposed by Liu and Branion and predicts the specific growth rate as a function of the concentration of substrate (Fe +2 ) and product (Fe +3 ). This expression is based on the thesis that growth of Thiobacillus ferrooxidans is competitively inhibited by product. The fit of this equation to the experimental data gives a high theoretical-experimental determination coefficient ( r 2 = 95%).

Comparison of industrially viable pretreatments to enhance soybean straw biodegradability.

This study explores acid and alkaline pretreatments in order to enhance soybean straw biodegradability. The effects of sulfuric acid and sodium hydroxide for different pretreatment times at 30°C and 121°C on biomass dissolution and the subsequent enzymatic hydrolysis were investigated. The highest total conversion to reducing sugars of 93.9% was attained when soybean straw was pretreated with acid (4% H2SO4, 121°C, 1 h) and subsequently subjected to the enzymatic process. However, conversion of 86.5%, were reached only with the hydrolysis of the pretreated residue using mild conditions, (0.5% NaOH, 30°C, 48 h), involving the reduction cost of the process. In addition to this, this result was dramatically decreased when pectinase was removed from the enzyme cocktail. It has been also demonstrated that the reduction of the enzyme loading to less than half allowed obtaining about 96% of the reducing sugars attained with the highest enzyme dose.

Optimum operating conditions in closed-system industrial acetifiers (semi-continuous operation): a study by computer simulation

Abstract This work analyzes the behaviour of an industrial acetification process in a closed system, by means of simulation techniques, testing several semi-continuous strategies, under different conditions of feed and discharge criteria. The simulator is based on a global model for the growth of Acetobacter aceti in submerged culture, which reflects the combined effects of acetic acid, ethanol and oxygen. The optimum operating conditions have been calculated for processes with both discharge at a set time and discharge at a set product concentration (acetic acid). In both cases, the effect on the evolution of the fermentation process by the ethanol and acetic acid concentration in the feed has been analyzed.

Viability reduction of Acetobacter aceti due to the absence of oxygen in submerged cultures

In this work, the influence that an aeration interruption may have upon acetic acid fermentation processes is studied. As a result, a kinetic model is proposed that foretells the cellular specific death rate in situations lacking in oxygen. Such a model collects the combined influences of substrate (ethanol) and product (acetic acid).

The influence of ripeness grade on the composition of musts and wines from Vitis vinifera cv. Tempranillo grown in a warm climate

Fruit ripeness has an influence on the phenolic and aromatic composition of grapes and musts and, therefore, on the sensorial characteristics of the resulting wine. The aim of the work described here was to assess the influence of the harvest date on the analytical composition of the musts and wines from the Vitis vinifera cv. Tempranillo grape grown in a warm climate. A hydroalcoholic medium was employed to extract the musts and simulate a traditional maceration process. Phenolic compounds were analysed by colorimetric methods and aroma compounds by gas chromatography/mass-spectrometry. Furthermore, the wines were tested by a sensory panel. A good correlation was obtained between the parameters measured in the must and in the corresponding wine, as well as in the scores recorded in the sensory analysis. In summary, grape ripening was found to have a marked influence on the wine composition and it was possible to establish the key parameters that need to be measured in the must during ripening to identify the optimal harvest date to obtain the best quality wine.