Adding enzymatically modified gelatin to enhance the rehydration abilities and mechanical properties of bacterial cellulose

Bacterial cellulose (BC) possesses excellent water holding capacity. However, increased crystallization causes a decrease in the rehydration ability of dried BC. Due to its excellent hydrophilic properties, we used gelatin and its enzymatically modified form (EMG) to prepare BC nano-composites in an attempt to enhance the rehydration abilities properties of BC. The polar peptide fraction was increased by extended hydrolysis of fish gelatin in Alcalase. Peptides smaller than 10 kDa were obtained by hydrolysis at 50 degrees C for 20 min. Protein contents of composites prepared by immersing BC in 5% gelatin (Gelatin/BC) or EMG (EMG/BC) solution were 81% and 92%, respectively, both of which then formed high gelatin/BC composites (HGBC). The protein content of EMG/BC was higher than that of Gelatin/BC, as compared with low gelatin/BC composites (LGBC) that were formed by immersion in a corresponding 0.5% solution. Among both HGBC and LGBC composites, EMG/BC exhibited the best rehydration abilities. Freeze-dried EMG/BC also exhibited the fastest rehydration rate and the best ability to restore wet-type composites. Composite microstructures revealed that BC was enveloped by gelatin when non-polar EMG (NPEMG) and polar EMG (PEMG) entered the BC network and adsorbed onto cellulose ribbons. The microstructure of EMG/BC contained both PEMG/BC and NPEMG/BC structures. Gelatin hydrolysates, penetrating BC networks and forming stable composites, improved the rehydration ability of dried BC. The polar functional groups of gelatin and its hydrolysates represent the key factors contributing to the hydrophilic nature of composites. (C) 2009 Elsevier Ltd. All rights reserved.