Moderate laccase-crosslinking improves the mechanical and thermal properties of acid-swollen collagen-based films modified by gallotannins

Using enzymatical crosslinking as a potential chemical-bonding alternative to improve collagen materials' properties is a challenge due to its relatively low efficiency. Here, the laccase-mediator system (LMS) with gallotannin (GT) as a mediator was introduced to acid-swollen collagen (ASC) films for its reinforcement. Hypothetically, laccase (Lac) in LMS oxidize GT to reactive quinone, which can attack ASC more easily compared to the direct catalyzation of Lac, resulting in an efficient crosslinking and related performance of ASC. We found that films with Lac from 3 to 12 U/g had increasing tensile strength (33.42 +/- 2.30 to 44.82 +/- 3.85 MPa), and with further addition of low-dose GT (0.1 mg/g) showed higher tensile strength (39.06 +/- 6.25 to 45.33 +/- 3.37 MPa). Meantime, denaturation temperature of Lac films gradually raised from 99.42 degrees C to 103.05 degrees C and those of GT-Lac films were higher ranging from 102.67 degrees C to 109.07 degrees C. We also observed that GT-Lac films presented smoother surfaces and more compact laminar cross-sections than those of Lac films, of which this excellent structure generally accompanied with low water wettability resulting from preventing water to penetrate the films. Moreover, the amide II and III peaks of GT-Lac films shifted to lower wavenumbers than those of Lac films, along with a less proportion of random coils (%) of ASC, partially supporting the hypothesis of LMS's crosslinking. In summary, the GT-contained LMS provides the potential to greenly modify collagenous materials extensively used in food industry, especially meat processing.