Dennis J. O'Brien

Ethanol production in a continuous fermentation/membrane pervaporation system

The productivity of ethanol fermentation processes, predominantly based on batch operation in the U.S. fuel ethanol industry, could be improved by adoption of continuous processing technology. In this study, a conventional yeast fermentation was coupled to a flat-plate membrane pervaporation unit to recover continuously an enriched ethanol stream from the fermentation broth. The process employed a concentrated dextrose feed stream controlled by the flow rate of permeate from the pervaporation unit via liquid-level control in the fermentor. The pervaporation module contained 0.1 m2 commercially available polydimethylsiloxane membrane and consistently produced a permeate of 20%–23% (w/w) ethanol while maintaining a level of 4%–6% ethanol in a stirred-tank fermentor. The system exhibited excellent operational stability. During continuous operation with cell densities of 15–23 g/l, ethanol productivities of 4.9–7.8 gl−1 h−1 were achieved utilizing feed streams of 269–619 g/l glucose. Pervaporation flux and ethanol selectivities were 0.31–0.79 lm−2 h−1 and 1.8–6.5 respectively.

Lipid-lipase interactions. I. Fat splitting with lipase fromCandida rugosa

Commercial dry lipase fromCandida rugosa (formerlyC. cylindracea) was used to catalyze hydrolysis of tallow, coconut oil and olive oil at 26–40 C. A methodology was developed to yield results reproducible within ±10% and to achieve essentially complete hydrolysis. From the hydrolysis data, an empirical relationship was developed that shows that the percentage of free fatty acid formed is almost a linear function of the logarithm of reaction time and the logarithm of enzyme concentration. A 95–98% hydrolysis of the 3 substrates was achieved experimentally in 72 hr, requiring 15 units lipase per milliequivalent (U/meq) of coconut oil or tallow and 6 U/meq of olive oil. The kinetics of lipolysis were determined for all 3 substrates and were found to approximate first order. Lipolysis rate was higher for olive oil than for tallow and coconut oil; no significant differences were observed between the latter 2 substrates. No statistically significant change in overall reaction rate was found when the hydrolysis was run at 26 C, 36 C or 46 C. Although the literature cites calcium or sodium ions and albumin as beneficial adjuvants to enzymatic lipolysis, these additives appeared to have no significant beneficial effect on the reaction. On the other hand, hydrocarbon solvents and nonionic surfactants showed an adverse effect.

Production of eicosapentaenoic acid by the filamentous fungus Pythium irregulare

Because of the diversity of their lipids and fatty acid biosynthetic pathways, lower fungi may find utilization as sources of omega-3 or other polyunsaturated fatty acids (PUFA). Production of eicosapentaenoic acid (EPA) by the filamentous fungus, Pythium irregulare, has been demonstrated in 14-1 fermentors. Sweet whey permeate (lactose) was preferred over glucose as a substrate for production of a high-EPA-content lipid. Characterization of the lipid indicated that approximately 90% of the EPA was contained in the neutral lipid fraction. A specific productivity of 24.9 mg EPA/g dry biomass was achieved at 14°C, at which temperature the lipid contained 25.5% EPA and 54.2% PUFA. This is the highest mycelial EPA content for a fungal lipid that has been reported in the literature.

Supercritical-fluid extraction of fungal lipids using mixed solvents: Experiment and modeling

Abstract Polyunsaturated fatty acids, notably eicosapentaenoic acid (EPA), have been purported to have beneficial physiological activity, including the prevention of arthritis and cardiovascular disease. A possible source of these fatty acids are filamentous fungi (e.g., Saprolegnia parasitica ). In this work, lipids are extracted directly from the fungal mycelia using supercritical CO 2 and CO 2 mixed with 10 wt % ethanol. Extractions are performed at temperatures from 40 to 60 °C and pressures from 205 to 680 bar. The recovery of lipid increases with increasing pressures and higher recoveries are obtained when a mixture of CO 2 with 10 wt % ethanol is used as the solvent (e.g., 89% recovered with 10% ethanol vs. 48% for 100% CO 2 ). The more polar CO 2 mixture is a better solvent since it is able to extract both the neutral and the polar lipid fractions. An unsteady extraction model which can give reliable representation of the entire extraction curve is presented. Mass transfer coefficients are computed using the experimental data, and these coefficients are correlated as a function of the interstitial velocity.

Separation and Recovery of Low Molecular Weight Organic Acids by Emulsion Liquid Membranes

Abstract Emulsion liquid membrane (ELM) extraction of low molecular weight organic acids resulting from whey fermentations was investigated. Rates of removal of lactic, acetic, propionic, and acrylic acids decreased as pH and concentration were increased. An ELM process for selective removal of acrylic acid from acrylic acid-propionic acid mixtures was developed through incorporation of a co-solvent (cyclohexanone) in the membrane phase of the emulsion. Degree of removal for each acid and, hence, selectivity among the acids appears to be determined by the water-membrane phase partition coefficient.

Identification of fungi for sweet whey permeate utilization and eicosapentaenoic acid production

SummaryEighteen selected organisms of theEumycota division of the fungi kingdom were examined for eicosapentaenoic acid production and utilization of sweet whey permeate. The organisms belong to the subdivisionsMastigomycotina, Zygomycotina, Ascomycotina andDeuteromycotina. Seven organisms were initially identified as lactose utilizers (the predominant sugar in sweet whey permeate_ and eicosapentaenoic acid (EPA) producers. Utilization of lactose was demonstrated and EPA production was confirmed for four organisms, all of the subdivisionMastigomycotina. Growth studies showed thatP. ultimum had the best potential for future work.

Supercritical-fluid extraction of fungal lipids: Effect of cosolvent on mass-transfer rates and process design and economics

Abstract The extraction of fungal lipids by supercritical CO 2 and CO 2 with 10 wt % ethanol was studied. The lipid solubility was measured from 40–60 °C and 200–700 bar, and was found to increase with increasing solvent pressure and temperature, although the crossover effect was observed. Mass transfer coefficients were fitted to experimental data and were found to increase with increasing solvent Reynolds number. No difference in mass-transfer coefficients was observed with the addition of the cosolvent. Using the experimental data, a mathematical model for a commercial extraction process was developed, and optimal values of the extractor pressure, solvent flow rate, and extraction time were computed. Since the lipid is more soluble in the CO 2 mixture, the optimal extractor pressure and extraction time were lower than those computed for a process with a pure CO 2 solvent. Capital and operating costs for the process were estimated and the addition of the cosolvent was found to lower the costs by over 40%. A comparison of the costs for the SFE process and the costs for a liquid-extraction process show that the SFE process is not competitive for this application, although the economics would be improved if wet fungal mycelia were contacted continuously with the supercritical solvent.

Recovery of Lysine from Corn Steepwater

ABSTRACT One approach to increasing the utilization of agricultural products is fractionation of low-value materials to yield high-value products. In this study, lysine recovery from corn steepwater, an internal processing stream generated in the wet-milling of corn, was investigated. A weakly acidic cation exchange resin was employed to selectively recover lysine from corn steepwater at pH 7.0. In column studies, the product from the ion exchange operation had a lysine content of 4–6% (db). The only other amino acid in the product was arginine. The presence of sodium, potassium, and magnesium ions at significant concentrations in the steepwater limited the lysine content of the product because of competitive adsorption on the resin. The lysine-enriched product reported here is 4–10 times higher in lysine content than other corn milling coproducts and could potentially be useful as a lysine supplement in animal feeds.