Characterization of edible films based on tilapia (Tilapia zillii) scale gelatin with different extraction pH

•Gelatin extracted from fish scales at pH 3 has high calcium content.•Transparent colorless gelatin films could be prepared from tilapia scales.•Gelatin extracted at pH 5 possesses excellent film-forming properties.•Strength of films is related to the α-helix structure of fish gelatin.

Gelatin was extracted from tilapia scales at pH ranges from 3 to 9, and the properties of resulting gelatin films were investigated. The ash and calcium contents in gelatin extracted at pH 3 was the highest compared to gelatin extracted at pH 5, 7 and 9. Amino acid composition of gelatin extracted at pH 3 was similar to that from pH 9, but was obviously different compared to that from pH 5 or pH 7. The films with higher tensile strength (TS) were prepared from scale gelatin extracted at pH 5, and the film strength became lower with increasing or decreasing extraction pH. On the other hand, the effect of gelatin extraction pH was not significant on WVP, color and transparency properties of films. When films were prepared with gelatin extracted at pH 3, although high molecular weight polymer and high glass transition temperature (Tg) were observed, the obtained films were not strong. Nevertheless, it is interesting to note a high correlation between TS of films and A1658/A1642 ratio derived from FTIR peak deconvolution. It is concluded that α-helix structures rather than molecular weight distribution and Tg were involved in the formation of gelatin films.

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