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Food Hydrocolloids 23 (2009) 2195–2203

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Food Hydrocolloids
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Adding enzymatically modified gelatin to enhance the rehydration abilities and mechanical properties of bacterial cellulose
Shih-Bin Lin, Chieh-Ping Hsu, Li-Chen Chen, Hui-Huang Chen*
Department of Food Science, National Ilan University,1 Sec. 1, Shen Nung Rd., Ilan City 260, Taiwan, ROC

a r t i c l e i n f o
Article history: Received 1 November 2008 Accepted 6 May 2009 Keywords: Bacterial cellulose Gelatin Hydrolyze Composite Rehydration

a b s t r a c t
Bacterial cellulose (BC) possesses excellent water holding capacity. However, increased crystallization causes a decrease in the rehydration ability of dried BC. Due toits 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  C for 20 min. Protein contents of compositesprepared 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 exhibitedthe 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/BCstructures. 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. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction When exuded from Gluconacetobacter xylinus, bacterial celluloses (BC)exhibit a simple straight chain polymer of glucose molecules linked at the b, 1–4 position (Blackwell, 1982; Thimman, 1968). Unlike cotton and paper, bacterial cellulose does not require remedial processing to remove unwanted polymers and contaminants (e.g., lignin, hemicellulose), and, therefore, retains a greater degree of polymerization, crystallization and water holding capacity (Klemm, Schumann,Udhardt, & Marsch, 2001). Such properties give BC widespread uses in the food industry in applications such as chewing gum, stabilizers, bulking agents and emulsifiers (Okiyama, Motoki, & Yamanaka, 1993; Wan et al., 2006). BC is also used in artificial skin, medicinal bandages and is a potential replacement for blood vessels in biomedicine (Shoda & Sugano, 2005; Wan et al., 2006; Wiegand, Elsner,Hipler, & Klemm, 2006). BC microfibrils are produced extracellularly by bacteria of the genus Gluconacetobacter. The microfibrils are in a ribbon form composed of subfibrils. Loci of subfibril biosyntheses form on the

* Corresponding author. Tel.: þ886 3 9357400x824; fax: þ886 3 9310722. E-mail address: (H.-H. Chen). 0268-005X/$ – see front matter Ó 2009 Elsevier Ltd. All rightsreserved. doi:10.1016/j.foodhyd.2009.05.011

surface of a bacterium as a linearly ordered array of terminal complexes (Brown Jr., Willison, & Richardson, 1976; Zaar, 1977). Each terminal complex produces nanometer-sized subfibrils that crystallize into a microfibril (Yamanaka, Ishihara, & Sugiyama, 2000). Although crystallization occurs soon after the glucan chains have been extruded from the...