Enzymatic Grafting of Peptides from Casein Hydrolysate to Chitosan. Potential for Value-Added Byproducts from Food-Processing Wastes

Abstract

Tyrosinase was used to initiate the grafting of peptides onto the amine-containing polysaccharide chitosan. Chemical evidence for covalent grafting was obtained from electrospray mass spectrometry for products formed from reactions with glucosamine (the monomeric unit of chitosan) and the model dipeptide Tyr-Ala. When this model dipeptide was incubated with tyrosinase and chitosan, there was a marked increase in the viscosity of the solution. This viscosity increase provides physical evidence that tyrosinase can initiate peptide grafting onto the chitosan backbone. A peptide-modified chitosan derivative was generated by reacting chitosan (0.32 w/v%) with acid-hydrolyzed casein (0.5 w/v %) using tyrosinase. After reaction, the peptide-modified chitosan was partially purified and dissolved in an aqueous acetic acid solution. Low concentrations of this peptide-modified chitosan were observed to confer viscoelastic properties to the solutions. Specifically they conferred high viscosities and shear thinning properties to the solutions, and solutions containing only 1 w/w % of the peptide-modified chitosan behaved as weak gels. Thus, tyrosinase provides a simple and safe way to convert food-processing byproducts into environmentally friendly products that offer useful functional properties. The selectivity of tyrosinase and the relatively high reactivity of chitosan's amines allow grafting to be performed with uncharacterized peptide mixtures present in crude hydrolysates.

Mimicking Biological Phenol Reaction Cascades to Confer Mechanical Function

“…The inset in Figure 1b shows two putative products that could be formed from the reaction of two glucosamine molecules with a single catechol. These putative products could be generated through intermediate Schiff-base linkages or Michael-type adducts, [35][36][37] and their expected M + 1 (mass of protonated molecular ion) peaks are observed at m/z values of 433 and 449. The indication that electrochemically oxidized catechol is capable of reacting with two glucosamines suggests that these reactions are capable of crosslinking chitosan.…”

Biomimetic Materials for Medical Application Through Enzymatic Modification

“…E oxy , E met and E deoxy are the three types of tyrosinase. E oxy D, E oxy M and E met D are E oxy -diphenol, E oxy -monophenol and E met -monophenol complexes organophosphorous hydrolase [20], green fluorescent protein [17,19], casein [1] and horseradish peroxidases [59]. As reported by Jee et al [55], the tyrosinasecatalyzed oxidation and crosslinking of tyrosine-containing peptides take place when the tyrosine residue is located in the N-terminus or in the middle of the peptide.…”

Effect of Trichoderma reesei tyrosinase on rheology and microstructure of acidified milk gels

“…Mushroom tyrosinase was reported to increase the viscosity of heatinduced milk protein gels prepared by addition of alginic acid and high-shear homogenization (Onwulata & Tomasula, 2008). Moreover, tyrosinases were also reported to induce formation of proteineoligosaccharide conjugates (Selinheimo, Lampila, Mattinen, & Buchert, 2008) and grafting of peptides onto polysaccharides (Aberg, Chen, Olumide, Raghavan, & Payne, 2004). Although very potent enzymes for protein cross-linking and structure modification, tyrosinases are not yet commercially available for large scale applications .…”