A comparative study of a fluidised bed reactor and a gas lift loop reactor for the IBE process: Part I. Reactor design and scale down approach

For the continuous production of isopropanol-butanol mixtures by immobilised Clostridium spp. (the IBE process) two reactor types were studied: a fluidised bed reactor with liquid recycling (FBR) and an external loop gas lift reactor (GLR). A large scale design (50–65 m³) was made for both reactors. A regime analysis, by evaluating the time constants for e.g. mixing and conversion, identified the ruling regime. Via the scale down approach two representative model reactors were developed: a 10 dm³ FBR reactor (H/D=25, D=0.08 m) and a 15 dm³ external loop GLR (H/D = 12.5, D_r=D_d=0.08 m). For both reactors the hydrodynamical behaviour and the total reactor performance were studied and are described in parts II and III of this study.     

Production of olive oil enriched with medium chain fatty acids catalysed by commercial immobilised lipases

Structured triacylglycerols, containing medium chain fatty acids, were produced by acidolysis of virgin olive oil with caprylic or capric acid, at a molar ratio of olive oil:fatty acid of 1:2, at 45 °C for 24 h, in solvent-free media or in n-hexane, catalysed by Thermomyces lanuginosa (Lipozyme TL IM), Rhizomucor miehei (Lipozyme RM IM) and Candida antarctica (Novozym 435) immobilised lipases. Incorporations were always greater for capric than for caprylic acid. For both acids, higher incorporations were always attained in solvent-free media: the highest caprylic acid incorporations were obtained with Novozym 435 (25.5 mol%) and Lipozyme RM IM (25.7 mol%), while similar capric acid incorporations were obtained with all biocatalysts (27.1–30.4 mol%).     

Inhibition of angiotensin I-converting enzyme by wheat gliadin hydrolysates

A tryptic gliadin hydrolysate was fractionated into peptide fractions, which were assigned to either the central domain (CD) or terminal domains (TD) of gliadins. The domains were expected to contain amino acid (AA) sequences which, when released from the parent protein, inhibit the angiotensin I-converting enzyme (ACE), which plays a key role in regulating blood pressure. A proline (Pro) poor TD related fraction, containing the smallest peptides, showed the highest ACE inhibitory activity (IC₅₀ = 0.33 mg/ml). Additional peptidases were selected based on their in silico predicted ability to release ACE inhibitory peptides. Further hydrolysis of the tryptic hydrolysate fractions with thermolysin, Clarex, Alcalase and Esperase increased ACE inhibitory activities. Immobilised Ni²⁺-ion affinity chromatography (IMAC) purification of a TD related peptide fraction obtained by sequential hydrolysis with trypsin and thermolysin yielded a fraction with an IC₅₀ value of 0.02 mg/ml. This IMAC fraction was enriched in histidine and hydrophobic AA (Pro, Val, Ile, Leu and Phe).     

Optimisation of polyacrylamide gel composition as support for enzyme immobilisation by covalent linking

A methodology based on experimental design to optimise a polyacrylamide gel as the support for enzyme immobilisation by covalent linking is described. A proper selection of the variables responsible for the gel structure, the amount of the linking agent, the support enzyme and suitable synthesis conditions lead to an increase in the activity retained by the gel. The maximum retained activity is chosen with the response surface methodology in terms of gel composition. © 2000 Society of Chemical Industry     

Steady state behaviour of three phase air lift bioreactors – an integrated model and experimental verification

Beneckea natriegens growing both in suspension and immobilised on diatomaceous earth (silica) support particles, in a 3 dm three phase air lift bioreactor (TPALB), was employed to demonstrate the relationship between substrate loading rate and immobilised biomass loading at steady state. Sterile conditions were maintained during the experiments, while the hydraulic conditions and the inlet flowrate remained constant. The experiment ran for 12 days, whilst the inlet substrate (n‐propanol) concentration was varied both upwards and downwards between 250 and 750 mg dm⁻³. The bulk liquid substrate concentration and the immobilised biomass loading were found to vary between 6–120 mg dm⁻³ and 71–159 mg(dry biomass) g⁻¹ (silica), respectively. The experimental results demonstrated that there is a positive relationship between substrate loading and immobilised biomass loading. A mathematical model is proposed to calculate biofilm thickness and bulk liquid substrate concentration (for steady state) using the inlet flowrate and the inlet substrate concentration as input parameters. The model was able to predict both biofilm thickness and immobilised biomass loading for the lower substrate loading rates applied. © 1999 Society of Chemical Industry     

HORACE BROWN MEMORIAL LECTURE A REALISTIC VIEW ON THE ROLE OF RESEARCH IN THE BREWING INDUSTRY TODAY

Present-day economic pressures stimulate technological innovations toward more rapid processing and to minimise both capital and production costs. Fermentation and maturation practices in most production plants are essentially unchanged from the low productivity batch processes. In terms of process economics two alternatives exist—moving to greater volume accelerated-batch processing and applying fully continuous high rate fermentation systems. Central to these issues are the growth controlling aspects of yeast performance in brewery fermentations. The importance of dissolved oxygen on lipid metabolism, yeast growth and beer flavour, the precise role of storage carbohydrates and the critical nature of the glycolytic/gluconeogenic junction in controlling fermentation performance are reviewed. The objectives of process optimisation are to build up sufficient yeast concentrations to gain optimal rate and extent of attenuation and desired flavour development whilst balancing but not over-expending wort nutrients for growth and maintenance. In this regard great promise may lie with new technologies including yeast oxygenation and immobilised cell systems. Particular emphasis is placed upon the ways in which this may be technically achieved and attention is drawn to the complexity of innovation management. Practical implications of factors benefiting and adversely affecting fermentation efficiency and beer flavour in both traditional and continuous immobilised cell systems are discussed.     

纤维素酶的应用研究进展

植物纤维原料是地球上极为丰富、廉价而又可再生的资源,它的利用一直是国内外的研究热点。纤维素酶是一种高活性生物催化剂,是一组能够降解纤维素生成葡萄糖的酶的总称,在食品、饲料、酿酒、纺织、中药提取和造纸等众多的工业领域有广泛的应用价值。     

Analytical effectiveness calculations concerning the formation of an inhibitive fermentation product associated with growth of biomass films immobilized in or around carriers

A reaction engineering model is presented for the bioproduction of chemicals associated with the growth of immobilized biomass in or around carriers. The model describes multiple-substrate diffusion limitations and first-order growth inhibition by one of the products. Analytical solutions are presented for intra-biofilm substrate and product concentrations, active biofilm thickness, biocatalyst effectiveness factor and degree of catalyst utilization. Simple criteria for optimal catalyst design are derived. Where applicable, the presented explicit analytical solutions for the biocatalyst effectiveness factor are much more convenient to incorporate into a macro-reactor model than the numerical alternatives.     

Intrinsic kinetic constants of an immobilised glucose-isomerase

The isomerization of glucose into fructose using a commercial immobilised glucose-isomerase has been studied and an initial transitory state of the enzyme, probably due to an establishment of stationary concentration profiles, was observed. Operational conditions to minimise the effects of external and internal mass transfer were determined using immobilised enzyme particles with diameters less than 0.064 mm. Thermal enzyme deactivation of the enzyme was insignificant if it was pre-treated with cobalt. The intrinsic kinetic constants of the reversible reaction Michaelis—Menten equation were calculated, in operational conditions free of mass transfer effects.