John Owusu

Effects of multi-frequency power ultrasound on the enzymolysis and structural characteristics of corn gluten meal

The aim of this study was to investigate the effect of multi-frequency power ultrasound (sweeping frequency and pulsed ultrasound (SFPU) and sequential dual frequency ultrasound (SDFU)) on the enzymolysis of corn gluten meal (CGM) and on the structures of the major protein fractions (zein, glutelin) of CGM. The results showed that multi-frequency power ultrasound pretreatments improved significantly (P<0.05) the degree of hydrolysis and conversion rate of CGM. The changes in UV-Vis spectra, fluorescence emission spectra, surface hydrophobicity (H0), and the content of SH and SS groups indicated unfolding of zein and glutelin by ultrasound. The circular dichroism analysis showed that both pretreatments decreased α-helix and increased β-sheet of glutelin. The SFPU pretreatment had little impact on the secondary structure of zein, while the SDFU increased the α-helix and decreased the β-sheet remarkably. Scanning electron microscope indicated that both pretreatments destroyed the microstructures of glutelin and CGM, reduced the particle size of zein despite that the SDFU induced aggregation was observed. In conclusion, multi-frequency power ultrasound pretreatment is an efficient method in protein proteolysis due to its sonochemistry effect on the molecular conformation as well as on the microstructure of protein.

Effects of multi-frequency power ultrasound on the enzymolysis of corn gluten meal: Kinetics and thermodynamics study.

The effects of multi-frequency power ultrasound (MPU) pretreatment on the kinetics and thermodynamics of corn gluten meal (CGM) were investigated in this research. The apparent constant (KM), apparent break-down rate constant (kA), reaction rate constants (k), energy of activation (Ea), enthalpy of activation (ΔH), entropy of activation (ΔS) and Gibbs free energy of activation (ΔG) were determined by means of the Michaelis-Menten equation, first-order kinetics model, Arrhenius equation and transition state theory, respectively. The results showed that MPU pretreatment can accelerate the enzymolysis of CGM under different enzymolysis conditions, viz. substrate concentration, enzyme concentration, pH, and temperature. Kinetics analysis revealed that MPU pretreatment decreased the KM value by 26.1% and increased the kA value by 7.3%, indicating ultrasound pretreatment increased the affinity between enzyme and substrate. In addition, the values of k for ultrasound pretreatment were increased by 84.8%, 41.9%, 28.9%, and 18.8% at the temperature of 293, 303, 313 and 323 K, respectively. For the thermodynamic parameters, ultrasound decreased Ea, ΔH and ΔS by 23.0%, 24.3% and 25.3%, respectively, but ultrasound had little change in ΔG value in the temperature range of 293-323 K. In conclusion, MPU pretreatment could remarkably enhance the enzymolysis of CGM, and this method can be applied to protein proteolysis industry to produce peptides.

Antioxidant peptides from corn gluten meal: Orthogonal design evaluation

Protamex catalyzed corn gluten meal (CGM) hydrolysis peptides (CHP) were prepared. Orthogonal design L16 (4(5)) was used to optimize processing variables of CGM concentration, CGM heat pretreatment (121 °C) time, and enzymolysis pH, temperature, and time. Degree of hydrolysis (DH), undigested residue ratio, molecular weight (MW) distribution and DPPH radical inhibition were selected as analysis indicators. Optimum variables were CGM concentration of 18%, heat pretreatment time of 40 min, and enzymolysis pH, temperature and time of 7.5, 55 °C and 24h, respectively. Verification test showed that CHP IC50 for scavenging hydroxyl radical was the best and then followed by reducing power. Oligopeptides improved after hydrolysis at the expense of di- and tripeptides, suggesting formation of soluble aggregates from low MW peptides. The increase in the DH, oligopeptides, Alanyl-Tyrosine, and antioxidant free amino acids coincided with the improvement in the antioxidant activity of CHP.

Effects and mechanism of ultrasound pretreatment on rapeseed protein enzymolysis

BACKGROUND The disadvantages which stem from the use of traditional enzymolysis of protein has necessitated the need to employ sweeping frequency and pulsed ultrasound (SFPU) in the pretreatment of rapeseed protein prior to proteolysis in order to bring about improvement in enzymolysis efficiency. Further, in order to determine the mechanism of ultrasound-accelerated enzymolysis of RP, the effects of SFPU on the kinetics, thermodynamics, molecular conformation and microstructure of RP were investigated. RESULTS Kinetic studies showed that SFPU pretreatment on RP improved enzymolysis by decreasing the apparent constant KM significantly (P < 0.05) by 32.8% and reducing the thermodynamic parameters Ea , ΔH and ΔS by 16.6%, 17.7% and 9.2% respectively. Fluorescence spectra revealed that SFPU pretreatment induced molecular unfolding, causing more hydrophobic groups and regions inside the molecules to be exposed to the outside. Circular dichroism analysis indicated that SFPU pretreatment decreased the α-helix content by 16.1% and increased the random coil content by 3.6%. In addition, scanning electron microscopy showed that SFPU pretreatment increased the specific surface area of RP. CONCLUSION Ultrasound pretreatment is an efficient method in RP proteolysis to produce peptides through its impact on the molecular conformation and microstructure of proteins.

Examining of athermal effects in microwave-induced glucose/glycine reaction and degradation of polysaccharide from Porphyra yezoensis.

Many reports claim the existence of athermal effects in microwave-induced reactions, and this challenge the assumption that the thermal effect (heating) is the sole factor in microwave heating. Therefore, microwave-induced Maillard reaction of d-glucose/glycine and degradation of polysaccharide from Porphyra yezoensis (PSPY) were investigated. Browning reactions were monitored by measuring heating rate, UV-absorbance and brown color, UV-vis and synchronous fluorescence spectra, GC/MS analysis and intrinsic viscosity of degradation. Heating of d-glucose/glycine solution produced brown compounds which were detected at A420, and the intermediate products, 2-acetylfuran and 5-methylfurfural, whose fluorescence intensity evidenced their formation. Maximum emission of synchronous fluorescence spectra of samples were at 430-440 nm and 370-390 nm. Both microwave and water bath heating did not cause any compositional changes in the Maillard reaction products. All data failed to show any significant athermal effects of compositional changes in the Maillard reaction products. It can be inferred that some of the reports suggesting the existence of athermal effects, which could ascribe to the different set-up obtained in not well temperature controlled microwave heating systems.

Influence of two inocula levels of Saccharomyces bayanus, BV 818 on fermentation and physico-chemical properties of fermented tomato (Lycopersicon esculentum Mill.) juice

To increase the production yield of functional recombinant streptavidin in Escherichia coli , the effects of host strains and culture conditions on expression of streptavidin with native C terminal (CNSA, amino acid residues 13 to 159) were investigated. Results show that the CNSA, encoded by the CNSA gene, was produced by E. coli BL21(DE3)pLysS strain in the inclusion body with a high yield up to 46.3% of the total cell protein (about 230 mg/g dry cell weight) after culture condition optimization. The dialysis method was adapted to refold CNSA and the refolding conditions were optimized. More than 90% of inclusion body protein was refolded to mature CNSA under optimized refolding conditions. The purity of the recombinant CNSA achieved 95.0% without using any affinity separation method. Enzyme linked immunosorbent assay (ELISA) analysis indicated that the biotin binding capability of our recombinant CNSA was similar to that of commercial products. Keywords: Streptavidin, Escherichia coli , protein refolding, recombinant proteinThe influence of two inocula levels of the yeast Saccharomyces bayanus, BV 818, 0.01 (w/v) and 0.02% (w/v) on physico-chemical properties of fermented tomato juice was investigated. The properties studied include alcoholic strength, dry extract, residual sugar, pH, titratable acidity and volatile acidity. During fermentation, the pH, titratable acidity, brix, CO2 production and changes in phenolic composition of the fermented juice were monitored. Both pH and titratable acidity showed an upward trend for the fermented juices. Alcoholic strength of the fermented juice produced with 0.01% (w/v) inoculum level was significantly higher (p<0.05) than that produced with 0.02% (w/v). The total phenolics and pH for wine obtained from 0.02% (w/v) inoculum level were significantly higher (p<0.05) than that from 0.01%. Volatile acidity values of both wines were below the permitted levels. During ageing, most colour parameters showed higher values in both fermented juices. Inoculum level 0.01% (w/v) gave better physico-chemical qualities and was therefore found to be better than 0.02% (w/v) in producing fermented tomato juice. The 0.01% (w/v) inoculum-fermented tomato juice scored higher for overall acceptance than that of 0.02% (w/v) inoculum-fermented tomato juice, but the acceptance levels were not significant.