Adsorption behavior of L-tryptophan on ion exchange resin

Adsorption and Separation of Aromatic Amino Acids from Aqueous Solutions Using Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are investigated for the adsorption of aromatic amino acids l-phenylalanine (l-Phe), l-tryptophan (l-Trp), and l-tyrosine (l-Tyr) from aqueous solutions. After screening a range of water-stable MOFs, the hydrophobic Zr-MOF MIL-140C emerged as the best performing material, exhibiting uptakes of 15 wt % for l-Trp and 20 wt % for l-Phe. These uptakes are 5-10 wt % higher than those of large-pore zeolites Beta and Y. Both single-compound and competitive adsorption isotherms for l-Phe and l-Trp were experimentally obtained at the natural pH of these amino acid mixtures (pH 6.5-7) without additional pH modification. We find that the hydrophobic nature of MIL-140C and the capacity of l-Trp to form hydrogen bonds favor the uptake of l-Trp with its larger indole moiety compared to the smaller phenyl side group of l-Phe. On the basis of literature and vibrational analysis, observations of hydrogen-bonded l-Trp within the MIL-140C framework are evidenced by red- and blue-shifted -NH vibrations (3400 cm^-1) in Fourier transform infrared spectroscopy, which were attributed to types N-H_l-Trp···π_MIL-140C and N-H_l-Trp···O_MIL-140C, respectively. MIL-140C is shown to be recycled at least three times for both aromatic amino acids without any loss of adsorption capacity, separation performance, or crystallinity. Desorption of aromatic amino acids proceeds easily in aqueous ethanol. Substantial coadsorption of negatively charged amino acids l-glutamate and l-aspartate (l-Glu and l-Asp) was observed from a model solution for wheat straw protein hydrolysate at pH 4.3. On the basis of these results, we conclude that MIL-140C is an interesting material for the recovery of essential aromatic amino acids l-Tyr, l-Phe, and l-Trp and of l-Glu and l-Asp from waste protein hydrolysates.

Optimization of Process Parameters forε-Polylysine Production by Response Surface Methods

ε-Polylysine (ε-PL) is a highly safe natural food preservative with a broad antimicrobial spectrum, excellent corrosion resistances, and great commercial potentials. In the present work, we evaluated theε-PL adsorption performances of HZB-3B and D155 resins and optimized the adsorption and desorption conditions by single-factor test, response surface method, and orthogonal design. The complexes of resin andε-PL were characterized by SEM and FITR. The results indicated that D155 resin had the bestε-PL adsorption performance and was selected for the separation and purification ofε-PL. The conditions for the static adsorption ofε-PL on D155 resin were optimized as follows:ε-PL solution 40 g/L, pH 8.5, resins 15 g/L, and absorption time 14 h. The adsorption efficiency ofε-PL under the optimal conditions was 96.84%. Theε-PL adsorbed on the D155 resin was easily desorbed with 0.4 mol/L HCl at 30°C in 10 h. The highest desorption efficiency was 97.57% and the overall recovery ofε-PL was 94.49% under the optimal conditions. The excellentε-PL adsorption and desorption properties of D155 resin including high selectivity and adsorption capacity, easy desorption, and high stability make it a good candidate for the isolation ofε-PL from fermentation broths.