Effect of pH and lactose on cross-linking extension and structure of fish gelatin films

Lactose-modified gelatin films were prepared at two different pHs and then, films were heated to promote the cross-linking reaction between gelatin and lactose. All films were transparent and homogeneous with hardly any pores (8-12%). The extension of the cross-linking reaction was assessed by means of film colour, solubility, and the formation of a fluorescence compound (pentosidine). It was observed that both pH and lactose affected the extension of the cross-linking reaction between the carbonyl group in lactose and the amino groups in gelatin. Films processed at native pH (5.4) showed higher decolouration and lower solubility, highlighting a further extension of cross-linking at this pH than at pH 2.0. Furthermore, the curve fitting of amide I and II profiles indicated that the secondary structure of gelatin films was also affected by lactose and pH.