Ljiljana Mojović

Rhizopus arrhizus lipase-catalyzed interesterification of the midfraction of palm oil to a cocoa butter equivalent fat

Abstract Celite-immobilized lipase from Rhizopus arrhizus was used to interesterify triacylglycerols of the palm oil midfraction with stearic acid in n-hexane. Under optimum conditions, acyl exchange occurred mainly between the palmitoyl group from the palm oil midfraction and the stearoyl group from the reaction mixture, giving an interesterified product whose fatty acyl composition was similar to that of cocoa butter. Addition of defatted soya lecithin significantly increased the substrate conversion. This was attributed to the formation of reverse micelles around the Celite-immobilized and hydrated enzyme that protected the enzyme from the nonpolar solvent and enhanced substrate and product diffusion in the enzyme microenvironment. The reverse micelle system exhibited higher productivity and operational stability when compared to the Celite-immobilized lipase.

Alginate-immobilized lipase by electrostatic extrusion for the purpose of palm oil hydrolysis in lecithin/isooctane system

Lipase from Candida rugosa was immobilized in alginate beads for possible application in non-aqueous or microaqueous reaction systems. An electrostatic droplet generation technique was used for production of small diameter (<1 mm) lipase-alginate beads. This technique provided negligible loss of the lipase (immobilization efficiencies were 98.2–99.2%). Under optimal immobilization conditions (applied potential 4.9 kV, needle gauge 21, 2% sodium alginate solution) the lipase-alginate beads, 0.65 mm in diameter, retained enzyme activity equivalent to 75% that of free lipase. The activity of the immobilized lipase was verified in the reaction of palm oil hydrolysis in a lecithin/isooctane system. The reaction rate with alginate-immobilized lipase was lower than with the free enzyme but the final conversions were approximately the same (∼74%). Immobilized lipase could be used for up to three reaction cycles with little loss of activity.

Palm oil hydrolysis by lipase from Candida cylindracea immobilized on zeolite type Y

Lipase from Candida cylindracea immobilized on hydrophobic zeolite type Y was used to hydrolyze palm oil in a microaqueous two-phase reaction system containing isooctane as organic medium and lecithin as surfactant. The lipase was immobilized to zeolite by adsorption. The maximum amount of bound protein at 8.2 mg g−1 and an immobilization efficiency of 33% were achieved under optimum conditions. The kinetics of lipase binding to zeolite were assessed by using the general model of topochemical reaction. Based on the values of the specific kinetic model parameters, we propose that the adsorption process is controlled by surface kinetics that was later experimentally confirmed. The activation energy for lipase adsorption on zeolite was 43 kJ mol−1. The lipase immobilized on zeolite had 35% of the activity of the free enzyme. After the seventh cycle, immobilized lipase retained 10% of the initial activity in palm oil hydrolysis.

PROGRESS IN THE PRODUCTION OF BIOETHANOL ON STARCH-BASED FEEDSTOCKS*

Bioethanol produced from renewable biomass, such as sugar, starch, or lignocellulosic materials, is one of the alternative energy resources, which is both renewable and environmentally friendly. Although, the priority in global future ethanol production is put on lignocellulosic processing, which is considered as one of the most promising second-generation biofuel technologies, the utilization of lignocellulosic material for fuel ethanol is still under improvement. Sugar-based (molasses, sugar cane, sugar beet) and starch-based (corn, wheat, triticale, potato, rice, etc.) feedstock are still currently predominant at the industrial level and they are, so far, economically favorable compared to lingocelluloses. Currently, approx. 80 % of total world ethanol production is obtained from the fermentation of simple sugars by yeast. In Serbia, one of the most suitable and available agricultural raw material for the industrial ethanol production are cereals such as corn, wheat and triticale. In addition, surpluses of this feedstock are being produced in our country constantly. In this paper, a brief review of the state of the art in bioethanol production and biomass availability is given, pointing out the progress possibilities on starch-based production. The progress possibilities are discussed in the domain of feedstock choice and pretreatment, optimization of fermentation, process integration and utilization of the process byproducts.

Kinetics of lipase-catalyzed hydrolysis of palm oil in lecithin/izooctane reversed micelles

Candida rugosa lipase has been used to investigate the hydrolysis of palm oil in a lecithin/isooctane reversed micellar system. The reaction obeys Michaelis-Menten kinetics for the initial conditions. Kinetic parameters such as maximum rate and Michaelis constant (Km) were determined for lipase-catalyzed hydrolysis in n-hexane and isooctane. According to the Km values, the enzyme affinity towards the substrate was increased in isooctane. The maximum degree of hydrolysis was generally decreased as the initial substrate concentration was increased. This may suggest that the hydrolysis in lecithin reversed micelles should be regarded as a one-substrate first-order reversible reaction. It is shown in this study that the proposed one-substrate first-order kinetic model can serve for the precise prediction of the degree of hydrolysis for a known reaction time or vice versa, when the initial substrate concentration is less than 0.325 mol/dm3. A disagreement with this model was found when the initial substrate concentration was higher than approximately 0.3 mol/dm3. This may be due to the effects of the products on lipase activity or even to the conversion of the reversed micellar system to other systems.

Lactic acid production on liquid distillery stillage by Lactobacillus rhamnosus immobilized onto zeolite.

In this study, lactic acid and biomass production on liquid distillery stillage from bioethanol production with Lactobacillus rhamnosus ATCC 7469 was studied. The cells were immobilized onto zeolite, a microporous aluminosilicate mineral and the lactic acid production with free and immobilized cells was compared. The immobilization allowed simple cell separation from the fermentation media and their reuse in repeated batch cycles. A number of viable cells of over 10(10) CFU g(-1) of zeolite was achieved at the end of fourth fermentation cycle. A maximal process productivity of 1.69 g L(-1), maximal lactic acid concentration of 42.19 g L(-1) and average yield coefficient of 0.96 g g(-1) were achieved in repeated batch fermentation on the liquid stillage without mineral or nitrogen supplementation.

The bioethanol production with the thin stillage recirculation.

In this paper, the bioethanol production with the thin stillage recirculation in mashing was investigated. The mashing was performed with recirculation of: 0, 10, 20 and 30 % of the thin stillage. The thin stillage recirculation was repeated six times. In the experiment without the thin stillage, the recirculation bioethanol yield (compared to the theoretical yield) was 97.96 %, which implicates that the experiment conditions were chosen and performed well. With the addition of the thin stillage, the bioethanol yield increased and was above 100 %. Higher bioethanol yield than 100 % can be explained by the fact that the thin stillage contains carbohydrates, amino acids and yeast cells degradation products. The bioethanol yield increased with the increased number of thin stillage recirculation cycles. Dry matter content in fermenting slurry increased with the increased thin stillage quantity and the number of the thin stillage recirculation cycles (8.04 % for the first and 9.40 % for the sixth cycle). Dry matter content in thin stillage increased with the increased thin stillage quantity and the number of thin stillage recirculation cycles. Based on the obtained results it can be concluded that thin stillage recirculation increased the bioethanol yield. The highest bioethanol yields were obtained with recirculation of 10% thin stillage.

Effect of different fermentation parameters on L-lactic acid production from liquid distillery stillage

Expansion of lactic acid applications, predominantly for the preparation of biodegradable polymers increased the research interest for new, economically favourable production processes. Liquid stillage from bioethanol production can be an inexpensive, valuable source of nutrients for growth of lactic acid bacteria. Utilisation of residual biomass with spent fermentation media as a functional animal feed can greatly influence the process value and its ecological aspect. In this paper, the kinetics of lactic acid and biomass production on liquid stillage by Lactobacillus rhamnosus ATCC 7469 was studied. In addition, the impact of temperature, inoculum concentration, shaking and pH control by addition of CaCO(3) was evaluated. Maximal lactic acid yield of 73.4%, as well as high biomass production (3×10(8) CFU ml(-1)) were achieved under selected conditions (41°C, 5% (v/v) of inoculum, 1% (w/v) of CaCO(3), initial pH of 6.5 and shaking rate of 90 rpm). These results were achieved without supplementation of the stillage with nitrogen or mineral sources.

Liposomes as Carriers of Antimicrobial Drugs

Liposome are promising drug carrier systems being developed. Their successful use in the treatment of several diseases demonstrates that a solid rationale for clinical development of liposomes as antimicrobial drug carriers can be established. There are a number of potential drug candidates for liposome encapsulation. The involvement of several biotechnology companies has culminated in the design and licensing of formulations for the treatment of certain microbial infections and cancers. Understanding of liposome behavior in the body and of the physicochemical mechanisms involved in the interaction of liposome, drug, and cellular targets is essential for their future applications.

Antifungal activity of oregano (Origanum vulgare L.) extract on the growth of Fusarium and Penicillium species isolated from food

The effect of the oregano extract (Origanum vulgare L.) on the growth of Fusarium and Penicillium species isolated from cakes and ready-for-use fresh salads from different kinds of vegetables was investigated. The contents of the active component of extract were identified by GC-MS and they include: carvacrol (34.2%), carvone (18.5%), p-cimene (8.05%), thymol (3.74%). The oregano extract showed the ability to reduce mould growth at all applied concentrations. Stronger inhibitory effect on the growth of Penicillium species, contrary to Fusarium, was determined. At extract concentration of 2.50 mL/100 mL, growth of P. aurantiogriseum, P. glabrum and P. brevicompactum was completely inhibited during 14 days of incubation. At the same concentration, growth of Fusarium proliferatum was inhibited by 81.71%, F. oxysporum by 85.84%, F. verticillioides by 86.50%, P. chrysogenum by 86.2% and F. subglutinans by 88.85%.