Kinetics, Modelling and Scaling-Up of Kojic Acid Fermentation by Aspergillus Flavus 44-1 Using Different Carbon Sources

Kojic acid production by Aspergillus flavus strain 44- 1 using different types of carbon source (glucose, starch hydrolysate from enzymatic hydrolysis of sago starch, sucrose, fructose and gelatinized sago starch) was carried out in 250 mL shake flask, 2 L, 8 L and 50 L stirred tank fermenters. The experimental data from batch fermentation and resuspended cell system were analysed in order to form the basis for a kinetic model of the process. Unstructured model based on logistic and Luedeking-Piret equations was found suitable to describe growth, substrate consumption and kojic acid production by Aspergillus flavus in batch and also resuspended cell system using either glucose or sucrose. From the modelling, it was found that kojic acid production by A. flavus was non-growth associated process. The kinetic parameter values for each fermenter were calculated from the modelling and they can be used to verify the experimental data using various types and concentration of carbon source. Kojic acid production (23.5 g/l) using 100 g/L sago starch in a shake flask was comparable to fermentation of glucose (32.5 g/L) and starch hydrolysate (27.9 g/L) but in the 8 L and 50 L fermenter kojic acid production was greatly reduced due to non-optimal aeration conditions. Fed-batch fermentation with intermittent feeding of concentrated sago starch (140 g/L) can be employed to improve direct fermentation of sago starch to kojic acid by about 4 times higher as compared to batch fermentation. A. flavus was also capable to utilise sucrose for kojic acid fermentation where the highest production (40.23 g/L) in 2 L fermenter was obtained at 150 g/L sucrose. Kojic acid production (10.25 g/L) was greatly reduced in fermentation using fructose as the sole carbon source. Scaling-up based on a constant impeller tip speed (1.65 m/s) together with optimal DOT and pH control strategies was successfully used for kojic acid fermentation in 50 L fermenter using glucose and sucrose as carbon sources. Kojic acid fermentation by A. flavus can be divided into two phases; growth and production phase. The culture pH during growth phase influenced the performance of kojic acid fermentation to a further extend than did the pH during the production phase. The fermentation without pH controlled (started with an initial culture pH 3) showed higher kojic acid production than single-phase pH controlled fermentation at a range of pH 2.2 - 4.0. Comparable kojic acid production to fermentation without pH controlled was obtained in two-phase pHcontrol led fermentation (started with initial culture pH, without control during growth phase and switched to 3 during production phase). Efficient conversion of glucose to kojic acid was achieved in a resuspended cell system, in a solution containing only glucose with citrate buffer at pH 3.5 and 3 0°C. The rate of glucose conversion to kojic acid was increased with increasing glucose concentration up to 100 g/L, suggesting that the biotransformation of glucose to kojic acid by the cell-bound enzymes fol lowed the Michaelis-Menten enzyme kinetic models. The value of Km and Vmax for the reaction, as determined by using Langmuir plot, was 10.042 g/L glucose and 0.076 g/L.h, respectively

Biotransformation of various carbon sources to kojic acid by cell-bound enzyme system of A. flavus Link 44-1

The ability of cell-bound enzyme of Aspergillus flavus Link 44-1 for production of kojic acid was studied in resuspended cell system. Cell material was produced in batch fermentation using 2 L stirred tank fermenter. The cell mycelia were then resuspended into 250 mL shake flask containing various carbon sources solution. Among the carbon sources tested, glucose gave the highest kojic acid yield based on carbon consumed (0.365 g/g) followed by sucrose (0.279 g/g), starch hydrolysate (0.212 g/g) and fructose (0.195 g/g). The rate of biotransformation was increased with increasing mycelial cell. Kojic acid production was also varied with different glucose and sucrose concentrations. The highest production was obtained at 100 g/L glucose and 100 g/L sucrose with a final kojic acid concentration of 45.3 and 33.4 g/L, respectively. The rate of biotransformation of glucose and sucrose to kojic acid followed the Michaelis–Menten equation, suggesting that the biotransformation rate vary with substrate concentration similar to the behaviour of many enzymes reaction

Wood reinvented

Lignocellulosic material which comprises lignin, hemicelluloses, and cellulose is a sustainable and renewable resource and it can come from forest and agricultural wastes and urban waste. 75 % of the lignocelluloses are made up of carbohydrates. Polysaccharides are the major cell wall constituents in the plant cell with the total amount up to 80 % of the total weight of the woody material. The simple sugar monomers in the polysaccharides can be converted into lactic acid through enzymatic hydrolysis and fermentation process

Improved mannan-degrading enzymes' production by Aspergillus niger through medium optimization.

The effect of different carbon and nitrogen sources on the production of mannan-degrading enzymes, focussing on β-mannanase, by Aspergillus niger was investigated using shake flask culture. The β-mannanase activity obtained during growth of A. niger on guar gum (GG, 1495 nkat mL−1) was much higher than those observed on other carbon substrates, locust bean gum (1148 nkat mL−1), α-cellulose (10.7 nkat mL−1), glucose (8.8 nkat mL−1) and carboxymethylcellulose (4.6 nkat mL−1). For fermentation using GG as a carbon source, bacteriological peptone gave the highest β-mannanase activity (1744 nkat mL−1) followed by peptone from meat (1168 nkat mL−1), yeast extract (817 nkat mL−1), ammonium sulphate (241 nkat mL−1), ammonium nitrate (113 nkat mL−1) and ammonium chloride (99 nkat mL−1) when used as a nitrogen source. The composition of bacteriological peptone and initial pH of the medium were further optimized using response surface methodology (RSM). Medium consisted of 21.3 g L−1 GG and 57 g L−1 peptone with initial culture pH of 5.5 was optimum for β-mannanase production (2063 nkat mL−1) by A. niger. The β-mannanase production obtained in this study using A. niger was significantly higher than those reported in the literature

The morphology and structure of red pigment producing fungus: monascus purpureus

Thered pigment producing, ascospore forming fungus Monascus purpureuswas obtained by monospore isolation and maintained on potato dextrose agar at 32°C for 7 days. M. purpureusproduces compact colonies of mycelia and accumulates large quantities of red pigment. Here we aimed to describe this newly isolated red pigment producing fungus using biochemical and microscopy technique. A newly isolated red pigment producing fungus from local red fermented rice was identified using Microbial Identification System based on fatty acids profiles.The growth, morphology, and structure of M. purpureuswere characterized by Scanning Electron Microscopy (SME). We found that M. purpureusreproduces sexually (by the formation of cleistothecium with ascospores) and asexual (by the formation of conidia). In Monascusspecies, the formation of either asexual or sexual spores appears to be an effective growth strategy. On the basis of biochemical and all morphological investigations it could be concluded that the new strain isolated from red fermented rice belongs to species M. purpureus, labeled as M. purpureus FTCC 5391

The gold particles

Light scattering techniques are widely used for determination of metal nanoparticle size. Metal nanoparticles are finding increasing application in the preparation of new nanocrystalline materials, with metal oxide composites being used to confer new electronic, magnetic, and optical properties into material structures

Improved protocol for the preparation of tetraselmis suecica axenic culture and adaptation to heterotrophic cultivation.

The effectiveness of various physical and chemical methods for the removal of contaminants from the microal-gae, Tetraselmis suecica, culture was investigated. The information obtained was used as the basis for the development of improved protocol for the preparation of axenic culture to be adapted to heterotrophic cultivation. Repeated centrifugation and rinsing effectively removed the free bacterial contaminants from the microalgae culture while sonication helped to loosen up the tightly attached bacterial contaminants on the microalgae cells. Removal of bacterial spores was accom- plished using a mixture of two antibiotics, 5 mg/mL vancomycine and 10 mg/mL neomycine. Walne medium formulation with natural seawater was preferred for the enhancement of growth of T. suecica. Adaptation of growth from photoautot- rophic to heterotrophic conditions was achieved by the repeated cultivation of photoautotrophic culture with sequential reduction in illumination time, and finally the culture was inoculated into the medium containing 10 g/L glucose, incu- bated in total darkness to obtain heterotrophic cells. Changes in the morphology and composition of T. suecica cells dur- ing the adaptation from photoautotrophic to heterotrophic condition, as examined under Transmission Electron Micro- scope, were also reported

Gas-liquid mass transfer performance of dual impeller system employing rushtons, concave-bladed disc (CD-6) turbines and their combination in stirred tank bioreactor

The degree of oxygenation in stirred tank bioreactor is normally described and characterized L by the volumetric gas-liquid mass transfer coefficient (kL a). Throughout this study, the gas liquid mass transfer performance of dual impeller stirring system employing either two Rushton turbines (RT), two Concave-bladed disc (CD-6) turbines or the combination of both was comparatively investigated in Newtonian and non-Newtonian fluid systems. Static gassing-out technique was applied in all experimental kLa determinations and subsequent modeling of mass transfer correlations for all configurations were developed by incorporating the effects of power number (N3D2) and superficial velocity (Vg) on kLa. Ultimately, the use of dual CD-6 stirrers on a mixing shaft improved the oxygen transfer rate (OTR) by about 5-50 % and 18-65 % higher than the conventional RT-RT system in Newtonian and non-Newtonian systems, respectively

Optimization and kinetic study on the synthesis of palm oil ester using Lipozyme TL IM

Enzymatic synthesis of palm oil esters (POE) was carried out via alcoholysis of palm oil (PO) and oleyl alcohol (OA) catalyzed by Lipozyme TL IM. The optimum reaction conditions were: temperature: 60 °C; enzyme load: 24.7 wt%; substrate ratio: 1:3 (PO/OA), impeller speed: 275 rpm and reaction time: 3 h. At the optimum condition, the conversion of POE was 79.54%. Reusability study showed that Lipozyme TL IM could be used for 5 cycles with conversion above 50%. The alcoholysis reaction kinetic follows the Ping-Pong Bi-Bi mechanism characterized by the Vmax, Km(PO), and Km(OA) values of 32.7 mmol/min, 0.3147 mmol/ml and 0.9483 mmol/ml, respectively. The relationship between initial reaction rate and temperature was also established based on the Arrhenius law

Characterization of headspace volatile flavor compounds formed during kefir production : application of solid phase microextraction.

Headspace volatile flavor compounds of kefir were monitored using headspace solid phase microextraction (HS-SPME) method during fermentation of milk with kefir starter culture. Among all flavor compounds, forty volatile compounds were initially detected using gas chromatography coupled to time-of-flight mass spectrometer (GC-TOFMS). Consequently, eight volatile flavor compounds, namely ethanol, ethyl acetate, ethyl butyrate, 2-butanone, acetone, 3-hydroxy-2-butanone (acetoin), 2,3-butanedione (diacetyl) and acetaldehyde were considered as the representative of the alcohol, ketone, ester and aldehyde compounds in kefir. Moreover, in term of quantitative analysis, more than 97% of total flavor compounds composed of the proposed volatile flavor compounds. The results indicated that the concentration of 2-butanone released into headspace of kefir was found to be stable during fermentation. The release content of other volatile flavor compounds increased throughout the fermentation process. However, the headspace concentration of acetoin significantly (P < 0.05) decreased between pH 5.2 and 4.6