Haluk Hamamci

Production of L(+)-lactic acid using immobilized rhizopus oryzae reactor performance based on kinetic model and simulation

The production of L(+)-lactic acid using alginate immobilizedRhizopus oryzae in tapered-column fluidized-bed batch reactor was tested and simulated using the kinetic data taken independently in shake-flask cultures. The data show saturation kinetics with substrate and product inhibitions in linear form. Analysis of the kinetic data gave kinetic constants:Vm, 11.04 g lactic acid/(L-bead. h);Km, 20.9 g glucose/L; andKi, 365 g glucose/L for lactic acid production. The product inhibition constant,Kp, was found to be 316 g lactic acid/L. The simulation results showed a good agreement with the experimental results when the initial lag phase was taken into account in the simulation model. Without the adjustment for the initial lag period, the kinetic model showed higher conversion. Starting with a glucose concentration of 150 g/L, it was possible to produce 73 g/L of L(+)-lactic acid in 44.5 h. The lactic acid yield was 64.8% by weight based on the amount of glucose consumed.

Synthesis and Rhizopus oryzae mediated enantioselective hydrolysis of α-acetoxy aryl alkyl ketones

Abstract Mn(OAc)3 oxidation of aromatic ketones afforded the α-acetoxy ketones in good yield. Selective hydrolysis of the acetoxy ketones by the fungus Rhizopus oryzae yields (R)-hydroxy ketones in high enantiomeric excess.

Fungal deracemization of benzoin

An enzyme system of Rhizopus oryzae (ATCC 9363) catalyzes the inversion of the chirality of benzoin via a deracemization reaction and, depending on the pH of the medium, both enantiomers of benzoin are obtained in good yield and high ee starting from rac-benzoin.

Simple chemoenzymatic access to enantiopure pharmacologically interesting (R)-2-hydroxypropiophenones

Abstract A chemoenzymatic synthesis of pharmacological interesting ( R )-2-hydroxypropiophenones starting from propiophenone derivatives is described. Manganese(III) acetate-mediated acetoxylation followed by fungus-mediated hydrolysis of propiophenone derivatives affords ( R )-2-hydroxypropiophenones in high enantiomeric excess.

Chemoenzymatic synthesis of (1S,2R)-1-amino-2-indanol, a key intermediate of HIV protease inhibitor, indinavir

The synthesis of (1S,2R)-1-amino-2-indanol, a key component of HIV protease inhibitor is accomplished in four steps starting from indanone efficiently and with high levels of diastereo- and enantioselectivity. The starting material is converted into 2-acetoxy-1-indanone involving Manganese (III) acetate oxidation . The 2-acetoxyketone is hydrolyzed to 2-hydroxy-1-indanone enantioselectively using Rhizopus oryzae. Selective reduction of 2-hydroxyoxime derivative, derived from the 2-hydroxyketone, gives the amino alcohol up to 98% diastereo- and enantioselectivity.

Effect of different stresses on trehalose levels in Rhizopus oryzae

Rhizopus oryzae accumulates and degrades trehalose in response to environmental stress conditions such as heat, osmotic stress, nitrogen starvation and pH. When heat stress was applied to R. oryzae, the trehalose content of the cells was increased from 0.9 to 4.8 mg/g dw and when the stress was relieved it decreased back to 1.1 mg/g dw. Under osmotic stress and nitrogen starvation, trehalose content was increased by 3.5 and 3 fold, respectively. The decrease in external pH increased trehalose level up to 2.6 mg/g dw from 1.1 mg/g dw. Increased trehalose level decreased back to normal after pH stress was relieved. These results indicate that trehalose accumulates and acts as a stress protectant in R. oryzae. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

One-step separation of β-galactosidase from β-lactoglobulin using water-in-oil microemulsions.

Solubilisation of β-galactosidase from Kluyveromyces lactis in Aerosol-OT water-in-isooctane microemulsions was measured as a function of buffer type and concentration, pH, and protein concentration. For buffer concentrations above ∼40mM, the enzyme was largely excluded from the droplets. Based on these results, a one-step separation was developed. A protein-containing aqueous feed was injected into an AOT/isooctane solution, with the feed volume slightly in excess of the predicted water solubility. Impurity proteins were entrapped inside the microemulsion droplets that then formed in the organic phase, while the high MW target protein was excluded and entered a newly formed, excess aqueous phase. The separation of β-galactosidase from the test protein β-lactoglobulin was most complete at 100mM KCl salt concentration, where the droplets were large enough to carry β-lactoglobulin but too small for β-galactosidase. At 100mM [KCl], 92% of the total enzyme activity was recovered in a concentrated and virtually pure form.

Cloning and expression of trehalose-6-phosphate synthase 1 from Rhizopus oryzae.

Trehalose is a reducing disaccharide acting as a protectant against environmental stresses in many organisms. In fungi, Trehalose‐6‐phosphate synthase 1 (TPS1) plays a key role in the biosynthesis of trehalose. In this study, a full‐length cDNA from Rhizopus oryzae encoding TPS1 (designated as RoTPS1) was isolated. The RoTPS1 cDNA is composed of 2505 nucleotides and encodes a protein of 834 amino acids with a molecular mass of 97.8 kDa. The amino acid sequence of RoTPS1 has a relatively high homology with the TPS1s in several other filamentous fungi. RoTPS1 was cloned into Saccharomyces cerevisiae and secretively expressed.

Rheological properties of lactose-free dairy desserts.

People suffering from lactose intolerance cannot digest milk or lactose-containing foods. Lactose-free diet is essential for them since they do not have the ability to produce lactase to breakdown milk sugar. Physical properties of lactose-free dairy desserts will most probably be different than that of lactose containing ones because of lactose hydrolysis. In this study, it was aimed to analyze the rheological and textural behaviors of different lactose-free dessert formulations containing different gum types and different waxy maize starch and sucrose concentrations. Waxy maize starch was used at concentrations of 0.032 g·mL−1, 0.040 g·mL−1, and 0.048 g·mL−1. In addition to waxy maize starch, guar gum, gum arabic, or κ-carrageenan at two different concentrations (1.0% w/w and 0.5% w/w) was added. Sucrose was added at concentrations of 0.14 g·mL−1 and 0.10 g·mL−1 in lactose-free desserts. Power law model was found to be suitable to explain the flow behavior of desserts. The storage and loss modulus of lactose-free desserts were higher than that of lactose-containing desserts. The κ-Carrageenan was found to be the most effective gum for structure build-up.