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.     

Extraction of flavonoids and carotenoids from Thai silk waste and antioxidant activity of extracts

Extraction of carotenoids and flavonoids from yellow Thai silk waste was investigated. The total recovery of 0.7 mg carotenoids and 5.1 mg flavonoids/g dry weight was obtained by ethanol extraction. Different methods for extractions of these pigments were carried out using two benign solvents: ethanol and subcritical water (SW) to determine the extraction efficiency of the solvents in various extraction conditions. For extraction of carotenoids, ethanol was suitable as extraction solvent and the amount of carotenoids increased with increasing temperature and extraction time. For flavonoids, SW extraction was suitable but the amount of flavonoids decreased with increasing SW temperature and extraction time due to decomposition at such conditions. In addition, the silk extracts were found to have low IC₅₀ values (15.6–23.3 μg/ml), the concentrations of the silk extracts that exhibit 50% reduction in 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), (ABTS) free radicals, thus indicating high antioxidant activities.     

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.     

Selective Extraction of Lutein from Alcohol Treated Chlorella vulgaris by Supercritical CO2

A pretreatment process using alcohol for the removal of chlorophyll a, b and β‐carotene from Chlorella vulgaris was developed to improve the yield and selectivity of lutein in the extract obtained by supercritical carbon dioxide extraction. Supercritical carbon dioxide extraction was carried out after pretreatment in the pressure range of 20 to 40 MPa and the temperature range of 40 to 80 °C. Ethanol and methanol were selected as elution solvents, of which ethanol was found most suitable for the elution, or pretreatment, process. The amounts of lutein and other compounds were analyzed by HPLC with the mixture of methanol and THF as the mobile phase. The amount of lutein in the extract increased with pressure, but decreased with extraction temperature. The highest recovery percentage and the selectivity of lutein were around 52.9 ± 0.02 % and 43.1 ± 0.02 %, respectively, obtained from supercritical carbon dioxide extraction with pretreatment and ethanol entrainer at 40 MPa and 40 °C.     

Reactions of C5 and C6-sugars, cellulose, and lignocellulose under hot compressed water (HCW) in the presence of heterogeneous acid catalysts

The benefit of TiO₂, ZrO₂ and SO₄-ZrO₂ on the reactions of C₅-sugar (xylose), C₆-sugar (glucose), cellulose, and lignocellulose was studied in hot compressed water (HCW) at 473-673 K with an aim to produce furfural and 5-hydroxymethylfurfural (HMF). TiO₂ and SO₄-ZrO₂ were found to active for hydrolysis and dehydration reactions producing high furfural and HMF yields with less by-products (i.e. glucose, fructose, xylose, and 1,6-anhydroglucose (AHG)) formation, whereas ZrO₂ was highly active for isomerization reaction; thus significant amount of fructose was observed in the liquid product.Importantly, it was also found that the starting salt precursor, the sulfur-doping content (for SO₄-ZrO₂) and the calcination temperature strongly affected the catalyst reactivity. Catalysts prepared from the chloride-based precursors (i.e. ZrOCl₂ and TiCl₄) gained higher reactivity compared to those prepared from nitrate-based precursors (i.e. ZrO(NO₃)₂ and TiO(NO₃)₂) due to their greater acidity, according to the NH₃- and CO₂-TPD studies. For SO₄-ZrO₂, among the catalyst with sulfur contents of 0.75%, 1.8% and 2.5%, SO₄-ZrO₂ with 1.8% sulfur content presented the highest acidity and reactivity toward hydrolysis and dehydration reactions. It is noted that the suitable calcination temperature for all catalysts was at 773 K; the XRD patterns revealed that different portions of phase formation was observed over catalysts with different calcination temperatures i.e. anatase/rutile for TiO₂ and monoclinic/tetragonal for ZrO₂ and SO₄-ZrO₂; the portion of these phase formations obviously affected the acidity-basicity of catalyst and thus the catalyst reactivity.     

Optimization of rubber seed oil extraction using liquefied dimethyl ether

The objective of this study was to find the optimal condition for the extraction of rubber seed oil (RSO), using liquefied dimethyl ether (DME). Response surface methodology with a spherical central composite design model was employed to determine the optimal extraction condition, consisting of a seed moisture content (%wt), a solvent to solid ratio (g/g), and an extraction temperature (°C). A quadratic regression equation suggested the optimal extraction condition was a moisture content of 56.4%wt, a solvent to solid ratio of 6.7 (g/g), and a temperature of 33.3?°C. At this condition, the RSO yield predicted by the model gave a slight deviation of 0.68% from the experimentally validated results (41.48 versus 41.20%). RSO has a kinematic viscosity of 36.8 cSt, an acid value of 10.7 KOH/g oil, a fatty acid content of 5.1% and an unsaturated fatty acid content of 80%, resulting in the potential production of biodiesel, biolubricants, and biodegradable plastics.     

Simultaneous Production of Biodiesel and Free Lutein from Chlorella vulgaris

Biodiesel and valuable free lutein were demonstrated to be simultaneously produced from Chlorella vulgaris lipid extracts. The alkali catalyst used in the transesterification of triglycerides acted as a reactant in converting lutein fatty acid esters to free lutein. A maximum biodiesel yield of 33.6 % by weight of the algal lipids was obtained after a 4‐h reaction with MeOH at the MeOH/biomass ratio of 16:1 using 6 % alkali catalyst. The excess of alkali and MeOH employed in the production of biodiesel ensured the complete saponification of all lutein fatty acid esters to free lutein, giving a maximum yield of 2.3 % by weight of the algal lipids. In addition, a process for the separation of the biodiesel and free lutein products from the reaction mixture is proposed. Finally, a preliminary economic assessment was conducted, the results of which suggest that the process for the simultaneous production of biodiesel and lutein from C. vulgaris may be economically feasible.     

Synthesis of LLDPE/TiO<Subscript>2</Subscript> nanocomposites by in situ polymerization with zirconocene/dMMAO catalyst: effect of [Al]/[Zr] ratios and TiO<Subscript>2</Subscript> phases

This article reveals the dependence of crystalline phases in titania on the intrinsic activity during in situ polymerization of ethylene/1-hexene using the zirconocene/dMMAO catalyst to produce LLDPE/TiO₂ nanocomposites. First, the TiO₂ nanoparticles having different crystalline phases were employed as the nanofillers by impregnation with dMMAO to obtain dMMAO/TiO₂. Then, copolymerization of ethylene/1-hexene using zirconocene catalyst was performed in the presence of dMMAO/TiO₂. It was found that the catalytic activity derived from the anatase TiO₂ (A) was about four times higher than that obtained from the rutile TiO₂ (R). This was likely due to higher intrinsic activity of the active species present on the TiO₂ (A). In addition, increased [Al]_dMMAO/[Zr]_cat ratios apparently resulted in enhanced activities for both TiO₂ (A) and TiO₂ (R). However, the TiO₂ (R) showed less deactivation upon increased [Al]_dMMAO/[Zr]_cat ratios. This can be attributed to strong interaction between dMMAO and TiO₂ (R) as proven by the TGA measurement. The microstructure of the LLDPE/TiO₂ obtained was found to be random copolymer for both TiO₂ (A) and TiO₂ (R).