ENHANCEMENT OF AMINO ACID PRODUCTION BY TWO-STEP AUTOLYSIS OF SPENT BREWER'S YEAST

A two-step autolysis process was proposed to enhance amino acid production from spent brewer's yeast. The technique was developed based on comparative study of the dynamics of production and release of proteins and amino acids during the autolysis of a concentrated suspension (22 wt.%) and a dilute yeast cell suspension (11.25 wt.%). The results suggest that, in the concentrated yeast suspension, proteins are more effectively broken down into amino acids, but the product release rate was lower due to a lower concentration gradient across the cell membrane. Thus, a two-step process, in which a high protein conversion occurred in a concentrated cell suspension during the first 13 h period, followed by a 26 h autolysis process within a dilute cell suspension, provided a higher overall yield of amino acids compared than the single-step process. The two-step process was found to result in a 25% higher amino acid yield with a weight fraction increase from 0.4 to 0.5 g/g dry wt. Other than these findings, the effect of adding NaCl to the suspension during autolysis was also investigated. It was found that, for the autolysis conditions employed in this study, the addition of NaCl did not significantly affect the production of protein but inhibited the production of amino acids.     

Biodiesel production from waste cooking palm oil using calcium oxide supported on activated carbon as catalyst in a fixed bed reactor

A reactor has been developed to produce high quality fatty acid methyl esters (FAME) from waste cooking palm oil (WCO). Continuous transesterification of free fatty acids (FFA) from acidified oil with methanol was carried out using a calcium oxide supported on activated carbon (CaO/AC) as a heterogeneous solid-base catalyst. CaO/AC was prepared according to the conventional incipient-wetness impregnation of aqueous solutions of calcium nitrate (Ca(NO₃)₂·4H₂O) precursors on an activated carbon support from palm shell in a fixed bed reactor with an external diameter of 60 mm and a height of 345 mm. Methanol/oil molar ratio, feed flow rate, catalyst bed height and reaction temperature were evaluated to obtain optimum reaction conditions. The results showed that the FFA conversion increased with increases in alcohol/oil molar ratio, catalyst bed height and temperature, whereas decreased with flow rate and initial water content in feedstock increase. The yield of FAME achieved 94% at the reaction temperature 60 °C, methanol/oil molar ratio of 25: 1 and residence time of 8 h. The physical and chemical properties of the produced methyl ester were determined and compared with the standard specifications. The characteristics of the product under the optimum condition were within the ASTM standard. High quality waste cooking palm oil methyl ester was produced by combination of heterogeneous alkali transesterification and separation processes in a fixed bed reactor. In sum, activated carbon shows potential for transesterification of FFA.     

Hydrothermal decomposition of yeast cells for production of proteins and amino acids

This study examines hydrothermal decomposition of Baker's yeast cells, used as a model for spent Brewer's yeast waste, into protein and amino acids. The reaction was carried out in a closed batch reactor at various temperatures between 100 and 250 degrees C. The reaction products were separated into water-soluble and solid residue. The results demonstrated that the amount of yeast residue decreased with increasing hydrolysis temperature. After 20 min reaction in water at 250 degrees C, 78% of yeast was decomposed. The highest amount of protein produced was also obtained at this condition and was found to be 0.16 mg/mg dry yeast. The highest amount of amino acids (0.063 mg/mg dry yeast) was found at the lowest temperature tested after 15 min. The hydrolysis product obtained at 200 degrees C was tested as a nutrient source for yeast growth. The growth of yeast cells in the culture medium containing 2 w/v% of this product was comparable to that of the cells grown in the medium containing commercial yeast extract at the same concentration. These results demonstrated the feasibility of using subcritical water to potentially decompose proteinaceous waste such as spent Brewer's yeast while recovering more useful products.     

Optimization of hydroxypropylmethylcellulose,yeast β-glucan,and whey protein levels based on physical properties of gluten-free rice bread using response surface methodology

Response surface methodology (RSM) was used to analyze effects of hydroxypropylmethylcellulose (HPMC), yeast β-glucan, and whey protein isolate (WPI) on physical properties of gluten-free bread baked from formulas based on rice starch. A Box–Behnken design with three independent variables (HPMC, yeast β-glucan, and WPI) and three levels was used to develop models for the different responses (physical properties). Individual contour plots of the different responses produced from the models were compared to the corresponding reference wheat bread data and were superimposed to locate gluten-free bread formulations that met the wheat bread standards for spread ratio, specific volume, hardness, cohesiveness, chewiness, and crumb color L∗ value. The optimal formulation, determined from the data, contained 4.35 g/100 g HPMC, 1 g/100 g β-glucan, and 0.37 g/100 g WPI, rice starch basis. Predicted values of the optimized bread were experimentally tested and compared with the experimental wheat bread data. A good agreement among these data was observed. Moreover, the optimized rice starch bread was found to be acceptable according to the results of sensory analysis.     

Influence of different β-glucans on the physical and rheological properties of egg yolk stabilized oil-in-water emulsions

The objective of this study was to obtain additional information on the influence of different β-glucan preparations, i.e. curdlan (CL), barley (BG), oat (OG), and yeast (YG) β-glucans, on the physical and rheological properties of egg yolk stabilized oil-in-water emulsions containing 20% oil. The emulsion without β-glucan (REF) was also prepared as a reference. Addition of CL and OG increased emulsion oil droplet sizes, whereas BG and YG showed no effect. Emulsion microstructures revealed that β-glucans induced flocculation of the oil droplet in the following order: CL > BG ≈ OG > YG. Dynamic oscillatory shear tests indicated that all emulsions exhibited weak gel-like characteristics which were enhanced by β-glucans addition as evidenced by an increase in G′ and a decrease in tan δ values. Flow tests showed that β-glucans enhanced thixotropy and yield stress of the emulsions. Stability tests demonstrated that β-glucans addition improved creaming stability of the emulsions during storage possibly due to an increase in viscosity of the continuous phase and/or a formation of a three-dimensional droplet network. CL exhibited the most pronounced effects on the aforementioned properties of emulsions compared to the other β-glucans tested. YG gave emulsion with higher viscoelastic properties and yield stress but lower stability than those made with BG or OG, indicating complex relationship between rheology and stability of these emulsion systems.     

Fabrication of scandium stabilized zirconia thin film by electrostatic spray deposition technique for solid oxide fuel cell electrolyte

A cost-effective and promising simple deposition method, electrostatic spray deposition (ESD), was used to fabricate dense scandium stabilized zirconia (ScSZ) thin films. The effect of solvent mixtures on their surface morphology was investigated. The films deposited using a mixed ethanol-butyl carbitol solvent with high boiling point showed higher smoothness compared with those deposited using ethanol and a mixture of ethanol and ethylene glycol, respectively. Single-phase ScSZ dense films were formed within 2 h at a low deposition temperature of 450 °C. Analysis of as heat-treated films using scanning electron microscope and atomic force microscope also indicated the formation of the uniform, smooth and dense thin films even at a low densification temperature. Furthermore, the ScSZ film deposited under the optimal condition showed the maximum in electrical conductivity of approximately 0.33 S cm^− 1 at a low operating temperature of 800 °C.     

Production of theophylline and polyethylene glycol 4000 composites using Gas Anti-Solvent (GAS) process

Production of drug composites can be used to enhance the dissolution rate of poorly-water soluble drugs. In this research, Gas Anti-Solvent (GAS) technique was applied to produce composites between theophylline (THEO) and polyethylene glycol (PEG) by using dense carbon dioxide as an anti-solvent. It was found that the size of the composites decreased as the concentration of PEG 4000 decreased. However, when increasing the temperature the degree of aggregation and particles size were increased. It was also found that a decrease in ethanol amount in the solvent mixture of dichloromethane and ethanol resulted in a decrease of particle size. The theophylline-PEG composites with the highest drug loading of 16.70% were obtained when using the mass ratio of drug and polymer at 2:3 wt.% in the dichloromethane and ethanol solvent of 50:50%v/v and 25 °C. The dissolution rate of the prepared composites in phosphate buffered solution was found to be 20.8 times greater than that of the original material.     

Closed-form solutions to discrete-time LQ optimal control and disturbance attenuation

This paper presents straightforward derivations of closed-form solutions to two discrete-time problems: linear-quadratic optimal control and disturbance attenuation. Then, as the main results, it shows how to reduce directly the closed-form solutions to their recursive forms. These recursive solutions are in the form of Riccati equation and, hence, establish a close relation between the closed-form solutions and the Riccati equations used in both problems.