RESUMEN
The green synthesis of silver nanoparticles (AgNPs) using the cell-free supernatant of a Haematococcus pluvialis culture (CFS) was implemented in the current study, under illumination conditions. The reduction of Ag+ to AgNPs by the CFS could be described by a pseudo-first-order kinetic equation at the temperature range tested. A high reaction rate during synthesis and stable AgNPs were obtained at 45 °C, while an alkaline pH (pH = 11.0) and a AgNO3 aqueous solution to CFS ratio of 90:10 (v/v) proved to be the most effective conditions in AgNPs synthesis. A metal precursor (AgNO3) at the concentration range tested (1-5 mM) was the limited reactant in the synthesis process. The synthesis of AgNPs was accomplished under static and agitated conditions. Continuous stirring enhanced the rate of reaction but induced aggregation at prolonged incubation times. Zeta potential and polydispersity index measurements indicated stable AgNPs and the majority of AgNPs formation occurred in the monodisperse phase. The X-ray diffraction (XRD) pattern revealed the face-centered cubic structure of the formed AgNPs, while TEM analysis revealed that the AgNPs were of a quasi-spherical shape with a size from 30 to 50 nm. The long-term stability of the AgNPs could be achieved in darkness and at 4 °C. In addition, the synthesized nanoparticles showed antibacterial activity against Escherichia coli.
RESUMEN
The aim of this study was to examine the potential enhancement of the antimicrobial activity of edible films, composed of (i) chitosan (CH), cellulose nanocrystals (CNC) and beta-cyclodextrin (CD) (50%-37.5%-12.5%) and (ii) hydroxypropyl methylcellulose (HPMC), cellulose nanocrystals (CNC) and beta-cyclodextrin (CD) (50%-37.5%-12.5%), with silver nanoparticle (AgNP) incorporationat levels 5, 10 and 15% v/v. According to the results, the AgNP addition led to very high antimicrobial activity of both films, reducing by more than 96% the microbial growth of the Gram-negative bacterium Escherichia coli (E. coli) in all cases. On the other hand, by adding AgNPs to films, their thickness as well as oxygen and water vapor permeability decreased, while their transparency increased. Furthermore, the contribution of these specific edible films to preserve cherries under cold storage was investigated. All edible coatings resulted in an improvement of the fruit properties under consideration, and especially the color difference, hardness and total microbial load.
RESUMEN
Xylanases have a broad range of applications in agro-industrial processes. In this study, we report on the discovery and characterization of a new thermotolerant GH10 xylanase from Bacillus safensis, designated as BsXyn10. The xylanase gene (bsxyn10) was cloned from Bacillus safensis and expressed in Escherichia coli. The reduced molecular mass of BsXyn10 was 48 kDa upon SDS-PAGE. Bsxyn10 was optimally active at pH 7.0 and 60 °C, stable over a broad range of pH (5.0-8.0), and also revealed tolerance toward different modulators (metal cations, EDTA). The enzyme was active toward various xylans with no activity on the glucose-based polysaccharides. KM, vmax, and kcat for oat spelt xylan hydrolysis were found to be 1.96 g·L-1, 58.6 µmole·min-1·(mg protein)-1, and 49 s-1, respectively. Thermodynamic parameters for oat spelt xylan hydrolysis at 60 °C were ΔS* = -61.9 J·mol-1·K-1, ΔH* = 37.0 kJ·mol-1 and ΔG* = 57.6 kJ·mol-1. BsXyn10 retained high levels of activity at temperatures up to 60 °C. The thermodynamic parameters (ΔH*D, ΔG*D, ΔS*D) for the thermal deactivation of BsXyn10 at a temperature range of 40-80 °C were: 192.5 ≤ ΔH*D ≤ 192.8 kJ·mol-1, 262.1 ≤ ΔS*D ≤ 265.8 J·mol-1·K-1, and 99.9 ≤ ΔG*D ≤ 109.6 kJ·mol-1. The BsXyn10-treated oat spelt xylan manifested the catalytic release of xylooligosaccharides of 2-6 DP, suggesting that BsXyn10 represents a promising candidate biocatalyst appropriate for several biotechnological applications.
Asunto(s)
Endo-1,4-beta Xilanasas , Xilanos , Bacillus , Endo-1,4-beta Xilanasas/química , Estabilidad de Enzimas , Escherichia coli/genética , Escherichia coli/metabolismo , Concentración de Iones de Hidrógeno , Hidrólisis , Cinética , Especificidad por Sustrato , Temperatura , Termodinámica , Xilanos/metabolismoRESUMEN
An extracellular acid stable α-amylase from Paecilomyces variotii ATHUM 8891 (PV8891 α-amylase) was purified to homogeneity applying ammonium sulfate fractionation, ion exchange and gel filtration chromatography and exhibited a reduced molecular weight of 75 kDa. The purified enzyme was optimally active at pH 5.0 and 60 °C and stable in acidic pH (3.0-6.0). K m, v max and k cat for starch hydrolysis were found 1.1 g L-1, 58.5 µmole min-1 (mg protein)-1, and 73.1 s-1, respectively. Amylase activity was marginally enhanced by Ca2+ and Fe2+ ions while Cu2+ ions strongly inhibited it. Thermodynamic parameters determined for starch hydrolysis (Ε α, ΔH*, ΔG*, ΔS*, Δ G E - S ∗ and Δ G E - T ∗ ) suggests an effective capacity of PV8891 α-amylase towards starch hydrolysis. Thermal stability of PV8891 α-amylase was assessed at different temperatures (30-80 οC). Thermodynamic parameters ( E a d , ΔH*, ΔG*, ΔS*) as well as the integral activity of a continuous system for starch hydrolysis by the PV8891 α-amylase revealed satisfactory thermostability up to 60 °C. The acidic nature and its satisfactory performance at temperatures lower than the industrially used amylases may represent potential applications of PV8891 α-amylase in starch processing industry.
RESUMEN
The main objective of the present study was to meticulously investigate an inclusive set of physicochemical and handle properties (determined through Kawabata evaluation system) of bioscoured cotton fabrics. The application of a commercial pectinase preparation, Bioprep 3000L, for a range of concentrations and treatment times, could create a pectin-free textile with low wax content. Multiple regression analysis was used to describe the effect of enzymatic process variables on pectin and waxes removal. Comparison of fabrics' properties such as wettability, whiteness, crystallinity index, and dyeing behaviour, confirmed that bioscouring could be as much effective as the conventional alkaline process. Uncovering the relationship between the composition of materials and their physicochemical properties was attempted. The application of higher enzyme concentrations generated fabrics with improved low-stress mechanical properties. Bending and shear rigidity, compressional resilience, as well as, extensibility of enzymatically treated cotton fabrics could be efficiently predicted by means of a single independent variable, the crystallinity index.