Convective Drying of Mango (Mangifera indica L.): Effect of Experimental Parameters on Drying Kinetics and Shrinkage

The aims of this work were to study the effect of swirling and non-swirling air flow on drying kinetics of ripe mango and to investigate the area shrinkage of ripe mango during the drying process by computer vision system (CVS). The CVS used to evaluate the area shrinkage of dried ripe mango is a real-time monitoring method which is precise, labor-saving, non-destructive method. In particular, CVS does not disrupt an equilibrium of heat and mass transfer in the drying chamber. Ripe mangoes were dried at air temperatures of 50, 60, and 70˚C and air velocities of 1.0, 1.5, and 2.0 m2/s for both swirling and non-swirling air flow. The results revealed that the effective moisture diffusivity (Deff), for swirling and non-swirling air flow drying, were (4.48–9.71)x10-9 and (3.41–7.24)x10-9 m2/s, respectively.  Moreover, the area shrinkage of swirling air flow drying was 32.64–40.98%, while that of non-swirling air flow drying was 36.45–43.44%. The area shrinkage of dried ripe mango was highest at low air temperature and 1.5 m/s air velocity

Expression, purification, and characterization of galactose oxidase of Fusarium sambucinum in E. coli

AbstractA gene encoding a galactose oxidase (GalOx) was isolated from Fusarium sambucinum cultures and overexpressed in Escherichia coli yielding 4.4mg enzyme per L of growth culture with a specific activity of 159Umg−1. By adding a C-terminal His-tag the enzyme could be easily purified with a single affinity chromatography step with high recovery rate (90%). The enzyme showed a single band on SDS–PAGE with an apparent molecular mass of 68.5kDa. The pH optimum for the oxidation of galactose was in the range of pH 6–7.5. Optimum temperature for the enzyme activity was 35°C, with a half-life of 11.2min, 5.3min, and 2.7min for incubation at 40°C, 50°C, and 60°C, respectively. From all tested substrates, the highest relative activity was found for 1-methyl-β-galactopyranoside (226Umg−1) and the highest catalytic efficiency (kcat/Km) for melibiose (2700mM−1s−1). The enzyme was highly specific for molecular oxygen as an electron acceptor, and showed no appreciable activity with a range of alternative acceptors investigated. Different chemicals were tested for their effect on GalOx activity. The activity was significantly reduced by EDTA, NaN3, and KCN

Galactose oxidase from Fusarium oxysporum--expression in E. coli and P. pastoris and biochemical characterization.

A gene coding for galactose 6-oxidase from Fusarium oxysporum G12 was cloned together with its native preprosequence and a C-terminal His-tag, and successfully expressed both in Escherichia coli and Pichia pastoris. The enzyme was subsequently purified and characterized. Among all tested substrates, the highest catalytic efficiency (kcat/Km) was found with 1-methyl-β-D-galactopyranoside (2.2 mM(-1) s(-1)). The Michaelis constant (Km) for D-galactose was determined to be 47 mM. Optimal pH and temperature for the enzyme activity were 7.0 and 40°C, respectively, and the enzyme was thermoinactivated at temperatures above 50°C. GalOx contains a unique metalloradical complex consisting of a copper atom and a tyrosine residue covalently attached to the sulphur of a cysteine. The correct formation of this thioether bond during the heterologous expression in E. coli and P. pastoris could be unequivocally confirmed by MALDI mass spectrometry, which offers a convenient alternative to prove this Tyr-Cys crosslink, which is essential for the catalytic activity of GalOx

Purification of recombinant GalOx expressed in <i>E. coli.</i>

<p>Purification of recombinant GalOx expressed in <i>E. coli.</i></p

Apparent kinetic constants of GalOx produced in <i>E. coli</i> for several electron donor substrates.

<p>Apparent kinetic constants of GalOx produced in <i>E. coli</i> for several electron donor substrates.</p

3D Structure of GalOx of <i>F. oxysporum</i>.

<p>A: Overall structure showing the predominantly β-structure. The N-terminus, C-terminus and the copper atom in the active site are highlighted. B: The active site of GalOx showing the copper ligands and the thioether cross-link. The structural model was generated by homology modelling based on the published structure of mature GalOx from <i>F. graminearum</i> (PDB 1gog) using SWISS_MODEL.</p

MALDI-FTMS data of the cross-linked peptides produced by in-gel digestion of GalOx. The cross-linked amino acids C230 and Y274 are highlighted.

<p>MALDI-FTMS data of the cross-linked peptides produced by in-gel digestion of GalOx. The cross-linked amino acids C230 and Y274 are highlighted.</p

Effect of the pH on the activity of GalOx expressed in <i>E. coli</i>.

<p>The buffers used were 50(♦), 50 mM phosphate (_▀) and 50 mM Tris (▴).</p

Temperature dependence of the activity of GalOx expressed in <i>E. coli.</i>

<p>Temperature dependence of the activity of GalOx expressed in <i>E. coli.</i></p

MALDI-TOF peptide mass map of GalOx expressed in <i>E. coli</i>.

<p>The peptides were generated by sequential digestion using trypsin and Asp-N. The peak labels correspond to the [M+H]⁺ ions of the obtained peptide fragments and their positions in the GalOx sequence. The spectrum also shows two intense signals (marked with asterisk) at m/z 2237.9 and 2374.9 related to the cross-linked peptides 266–274/312–323 and 265–274/312–323, respectively. The identity of the cross-linked peptides was verified by MS/MS fragmentation.</p