Properties and Applications of Bio-nanocomposite Film based on Gelatin and Nanoclay

Abstract

Gelatin from splendid squid (Loligo formosana) skin extracted at different temperatures (50-80 °C) and their corresponding films were characterized. Gelatin extracted at 80 °C showed the highest yield (45.3%, dry weight basis) with relatively higher free amino group content (P<0.05). However, gelatin extracted at 50 °C (G50) had the highest gel strength (P<0.05). G80 had the higher a* value, compared with others (P<0.05). When films from those gelatins were prepared, tensile strength (TS) and elongation at break (EAB) of films decreased, but water vapor permeability (WP) increased (P<0.05) as the extraction temperature increased. Increase in transparency value with coincidental decrease in lightness was observed with increasing extraction temperatures. Thermogravimetric analysis (TGA) indicated that film prepared from G80 (F80) exhibited the higher heat susceptibility and weight loss. Loosen structure was observed in film prepared from gelatin with increasing extraction temperatures. Gelatins obtained from bleached (0-8% H2O2 w/v) squid skin and films from those gelatins were characterized. Gelatin from skin bleached with higher H2O2 concentrations had higher yield, lower free amino group and carbonyl group contents than the control gelatin (P<0.05). Gel strength of gelatin generally decreased as H2O2 concentrations increased (P<0.05). Gelatin prepared from skin bleached with 2% H2O2 showed the highest L", but lowest AE*-values (P<0.05). H2O, at higher concentrations yielded gelatin with increasing b*value. TS and WVP of films decreased, but EAB increased (P<0.05) as the concentration of H2O2 increased. TGA indicated that heat susceptibility and weight loss of different films varied with H2O2 concentrations. Rougher surface was obtained in gelatin films prepared from skin bleached with H2O2 concentrations above 4%. The impacts of hydrophilic and hydrophobic montmorillonite (MMT) nanoclays at various levels (0-10%, w/w) on properties of tilapia skin gelatin films were investigated. Generally, mechanical properties were improved by the addition of Cloisite Nat in the range of 0.5-5% (w/w). The lowest WVP was observed for films incorporated with Cloisite Nat and Cloisite 20A at a level of 1% (w/w) (P<0.05). Wide angle X-ray diffraction (WAXD) and scanning electron microscopic (SEM) analyses revealed the intercalated/exfoliated structure of films. Homogeneity and smoothness of film surface decreased with the addition of both nanoclays. The incorporation of nanoclays enhanced the rigidity and heat stability of films. Tilapia skin gelatin films incorporated with hydrophilic and hydrophobic nanoclays with the aid of homogenization using different pressure levels (1000 to 4000 psi) and passes (2 and 4) were characterized. YM, TS and EAB of films decreased and WVP increased with increasing pressure levels and number of passes. Films incorporated with Cloisite 20A exhibited the lower WVP than those with Cloisite Nat Transparency of films increased when homogenization pressure and number of passes increased. Nanocomposite films prepared using homogenization had exfoliated structure, whilst those prepared without homogenization exhibited intercalated structure. TGA and DSC analyses indicated that thermal stability of nanocomposite films varied with homogenization condition. Effects of various pHs (4-8) of film forming suspensions (FFS) on the properties of nanocomposite film based on tilapia skin gelatin and Cloisite Nat were investigated. In general, mechanical and water vapor barrier properties of nanocomposite films were improved when FFS having pH 6 was used. Intercalated/exfoliated structure of nanocomposite films was revealed by WAXD analysis. Homogeneity and smoothness of film surface were obtained for nanocomposite films with pH 6 as confirmed by SEM micrographs. Thermal stability of nanocomposite films varied with different pH levels. Effects of ethanolic extract from coconut husk (EECH) at 0-0.4% (w/w) on properties of films and nanocomposite films from tilapia skin gelatin were investigated. YM, TS and EAB of both films decreased with addition of EECH (P<0.05). The lowest WVP was obtained for gelatin film and nanocomposite film containing 0.05% and 0.4% EECH (w/w), respectively (P<0.05). Generally, a* value of films increased (P<0.05) with increasing levels of EECH, regardless of nanoclay incorporation. Intercalated or exfoliated structure of nanocomposite films was revealed by WAXD analysis. Based on SEM analysis, the rougher surface was found when EECH was added. EECH had varying impact on thermal stability of films. When tilapia and squid skin gelatin films and nanocomposite films incorporated without and with EECH were used to cover mackerel meat powder, quality changes were monitored in comparison with that covered with polyethylene (PE) film and the control (without covering) during storage of 30 days at 28-30 °C. The powder covered with nanocomposite film incorporated with EECH at 0.4% (w/w) (SGF-Na-EECH) generally had the lower moisture content than those covered with other gelatin films throughout the storage. The lower PV, TBARS, TVB and pH were observed for SGF-Na-EECH sample than PE sample and the control (P<0.05). Based on SPME-GCMS analysis, SGF-Na-EECH sample contained the lower volatile lipid oxidation products. Higher overall likeness score was observed for SGF-Na-EECH sample on day 30 of storage. Therefore, fish and squid gelatins could be used as biomaterials for film preparation. The improvement of film properties could be achieved by incorporation of nanoclay, especially in combination with EECH. The film could extend the shelf-life of dried mackerel powder, mainly via the prevention of lipid oxidation.