Kuan-Chen Cheng

Pullulan: biosynthesis, production, and applications

Pullulan is a linear glucosic polysaccharide produced by the polymorphic fungus Aureobasidium pullulans, which has long been applied for various applications from food additives to environmental remediation agents. This review article presents an overview of pullulan’s chemistry, biosynthesis, applications, state-of-the-art advances in the enhancement of pullulan production through the investigations of enzyme regulations, molecular properties, cultivation parameters, and bioreactor design. The enzyme regulations are intended to illustrate the influences of metabolic pathway on pullulan production and its structural composition. Molecular properties, such as molecular weight distribution and pure pullulan content, of pullulan are crucial for pullulan applications and vary with different fermentation parameters. Studies on the effects of environmental parameters and new bioreactor design for enhancing pullulan production are getting attention. Finally, the potential applications of pullulan through chemical modification as a novel biologically active derivative are also discussed.

Biosynthesis, production and applications of bacterial cellulose

Bacterial cellulose (BC) as a never-dried biopolymer synthesized in abundance by Gluconacetobacter xylinus is in a pure form which requires no intensive processing to remove unwanted impurities and contaminants such as lignin, pectin and hemicellulose. In contrast to plant cellulose, BC, with several remarkable physical properties, can be grown to any desired shape and structure to meet the needs of different applications. BC has been commercialized as diet foods, filtration membranes, paper additives, and wound dressings. This review article presents an overview of BC structure, biosynthesis, applications, state-of-the-art advances in enhancing BC production, and its material properties through the investigations of genetic regulations, fermentation parameters, and bioreactor design. In addition, future prospects on its applications through chemical modification as a new biologically active derivative will be discussed.

Enhanced production of bacterial cellulose by using a biofilm reactor and its material property analysis.

Bacterial cellulose has been used in the food industry for applications such as low-calorie desserts, salads, and fabricated foods. It has also been used in the paper manufacturing industry to enhance paper strength, the electronics industry in acoustic diaphragms for audio speakers, the pharmaceutical industry as filtration membranes, and in the medical field as wound dressing and artificial skin material. In this study, different types of plastic composite support (PCS) were implemented separately within a fermentation medium in order to enhance bacterial cellulose (BC) production by Acetobacter xylinum. The optimal composition of nutritious compounds in PCS was chosen based on the amount of BC produced. The selected PCS was implemented within a bioreactor to examine the effects on BC production in a batch fermentation. The produced BC was analyzed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Among thirteen types of PCS, the type SFYR+ was selected as solid support for BC production by A. xylinum in a batch biofilm reactor due to its high nitrogen content, moderate nitrogen leaching rate, and sufficient biomass attached on PCS. The PCS biofilm reactor yielded BC production (7.05 g/L) that was 2.5-fold greater than the control (2.82 g/L). The XRD results indicated that the PCS-grown BC exhibited higher crystallinity (93%) and similar crystal size (5.2 nm) to the control. FESEM results showed the attachment of A. xylinum on PCS, producing an interweaving BC product. TGA results demonstrated that PCS-grown BC had about 95% water retention ability, which was lower than BC produced within suspended-cell reactor. PCS-grown BC also exhibited higher Tmax compared to the control. Finally, DMA results showed that BC from the PCS biofilm reactor increased its mechanical property values, i.e., stress at break and Youngs modulus when compared to the control BC. The results clearly demonstrated that implementation of PCS within agitated fermentation enhanced BC production and improved its mechanical properties and thermal stability.

Advances in biofilm reactors for production of value-added products

Biofilms are defined as microbial cell layers, which are irreversibly or reversibly attached on solid surfaces. These attached cells are embedded in a self-produced exopolysaccharide matrix, and exhibit different growth and bioactivity compared with suspended cells. With their high biomass density, stability, and potential for long-term fermentation, biofilm reactors are employed for the fermentation and bioconversion, which need large amount of biomass. During the past decade, biofilm reactors have been successfully applied for production of many value-added products. This review article summarizes the applications of biofilm reactors with different novel designs. Advantages and concerns using biofilm reactors, potential uses for industrial-scale production, and further investigation needs are discussed.

Soyfoods and soybean products: from traditional use to modern applications

Soybean products (soyfoods), reported as potential functional foods, are implicated in several health-enhancing properties, such as easing the symptoms of postmenopausal women, reducing the risk of osteoporosis, preventing cardiovascular disease, and antimutagenic effects. Isoflavone, for example, is one of the most important compounds abundantly found in soybean, mainly accounting for the health-enhancing properties as mentioned earlier. However, most biological activities of isoflavones are mainly attributed to their aglycone forms. It has also been demonstrated that isoflavone aglycones are absorbed faster and in greater amount than their glycosides in human intestines. Fortunately, deglycosylation of isoflavones can be achieved during fermentation process by several strains such as lactic acid bacteria, basidiomycetes, filamentous fungus, and Bacillus subtilis with their β-glucosidase activity. This article presents an overview of soybean’s chemistry, application, state-of-the-art advances in soybean fermentation processing and products as well as their applications in food and pharmaceutical industries. Different compounds, such as isoflavone, dietary fibers, and proteins which exhibit significant bioactivities, are summarized. The roles of different microorganisms in bioconversion and enhancement of bioactivities of fermented soybean are also discussed.

Effects of CMC addition on bacterial cellulose production in a biofilm reactor and its paper sheets analysis.

Bacterial cellulose (BC) can be grown into any desired shape such as pellicles, pellets, and spherelike balls, depending on the cultivation method, additives, and cell population. In this study, Acetobacter xylinum (ATCC 700178) was grown in the production medium with different concentrations of carboxylmethylcellulose (CMC) and were evaluated for BC production by using a PCS biofilm reactor. The results demonstrated that BC production was enhanced to its maximum (∼13 g/L) when 1.5% of CMC was applied, which was 1.7-fold higher than the result obtained from control culture. The major type of the produced BC was also switched from BC pellicle to small pellets. The ratio of BC pellets in suspension increased from 0 to 93%. Fourier transform infrared (FTIR) spectroscopy demonstrated that CMC was incorporated into BC during fermentation and resulted in the decreased crystallinity and crystal size. The X-ray diffraction (XRD) patterns indicated that CMC-BC exhibited both lower crystallinity (80%) and crystal size (4.2 nm) when compared with control samples (86% and 5.3 nm). The harvested BC was subjected to paper formation and its mechanical strength was determined. Dynamic mechanical analysis (DMA) results demonstrated that BC paper sheets exhibited higher tensile strength and Youngs modulus when compared with regular paper.

Statistical optimization of culture media for growth and lipid production of Chlorella protothecoides UTEX 250

The concentration of NaNO(3), MgSO(4) · 7H(2)O and proteose, in Chlorella protothecoides medium were optimized for algal biomass and lipid production by using response surface methodology with Box-Behnken design. The optimal concentrations were 0.45 g/L of NaNO(3), 6 mg/L of MgSO(4) · 7H(2)O, and 0.25 g/L of proteose for maximum biomass production and 2 mg/L of MgSO(4) · 7H(2)O and no addition of NaNO(3) and proteose for lipid accumulation. In optimized biomass production medium, a final biomass concentration of 1.19 g/L was obtained, which was 1.8 times higher than that in the original medium. For lipid accumulation, a 12.9% lipid content was obtained from the biomass in the lipid production medium, which was three times higher than that from the original medium. The fatty acid profile of algae grown in the optimized medium demonstrated a higher unsaturated fatty acid content (i.e. methyl linoleate (C18:2) and methyl linolenate (C18:3)) than that of the algae grown in the original medium. The results provide a strategy for limiting the amount of nutrients required in large scale outdoor cultivation systems of C. protothecoides to make the production of algal biomass more economically attractive.

Enrichment of two isoflavone aglycones in black soymilk by using spent coffee grounds as an immobiliser for β-glucosidase.

Spent coffee grounds, discarded as environmental pollutants, were adopted as enzyme immobilisation solid carriers instead of commercialised solid supports to establish an economical catalytic system. β-Glucosidase was covalently immobilised onto spent coffee grounds for the conversion of isoflavone glycosides into their aglycones in black soymilk. Optimum conditions were determined to be 40°C and pH 6 using 4-nitrophenyl β-D-glucuronide as an indicator. Operational reusability was confirmed for more than 30 batch reactions and the storage stability was capable of sustaining its highest catalytic activity for 20 days. The kinetic parameters including rate constant (K), time (τ(50)) in which 50% of isoflavone deglycosylation was reached, and time (τ(complete)) required to achieve complete isoflavone deglycosylation, were 0.16±0.02 min(-1), 4.54±0.32 min, 60 min for daidzin and 0.16±0.02 min(-1), 2.28±0.11 min, 60 min for genistin, respectively. The total aglycone content in black soymilk was enriched by 67.14±0.60% in the enzymatic treatment of 60 min duration.

Bioethanol production from taro waste using thermo-tolerant yeast Kluyveromyces marxianus K21

In the present study, evaluation and optimization of taro waste (TW), which was mainly composed of taro peels that contain many starch residues, as the main carbon source in medium were studied. The flask studies showed the optimal medium was using 170g/L of TW which is about 100g/L of glucose and 9g/L of CGM as alternative nitrogen source. Simultaneous saccharification and fermentation (SSF) exhibited higher bioethanol productivity toward separation hydrolysis and fermentation (SHF). The optimal condition of SSF was 5% of Kluyveromyces marxianus K21 inoculum at 40°C resulting in the maximum ethanol concentration (48.98g/L) and productivity (2.23g/L/h) after 22h of cultivation. The scaling up experiment in a 5L bioreactor demonstrated that K21 can still maintain its capability. After 20h of cultivation, 43.78g/L of ethanol (2.19g/L/h of productivity) was achieved corresponding to a 94.2% theoretical ethanol yield.

Evaluation of Medium Composition and Fermentation Parameters on Pullulan Production by Aureobasidium pullulans

The goal of this study was to enhance pullulan production by evaluating the effects of different fermentation parameters. Various carbon sources and their concentrations, yeast extract (YE) concentrations, fermentation temperatures and various pH profiles were examined. The optimal growth condition for pullulan production by Aureobasidium pullulans has been found as 75 g/L of sucrose as carbon source, 3 g/L of YE and cultivation temperature at 30 °C. Under these conditions with an initial pH at 5, 20.7 g/L of final pullulan concentration and 0.22 g/L/h maximum production rate were obtained. Later on, various pH profiles, agitation speeds, aerations and fed-batch fermentation were evaluated. The results demonstrated that pullulan production was enhanced to 25.8 g/L after 7-day cultivation with a 0.68 -g/L/h maximum production rate. There was no significant improvement of pullulan production from fed-batch fermentation. The optimal kinetics parameters were as follows: initial pH at 2.0, switched to pH 5.0 after 72 h and kept constant; agitation speed at 200 rpm; aeration at 1.5 vvm. The quality analysis demonstrated that the pullulan content produced from optimal conditions was 94.5% and its viscosity was 2.3 centipoise (cP). Fourier transform infrared spectroscopy also suggested that pullulan dominated the produced exopolysaccharide.