Utilization of frozen and salted Nile tilapia skin for batch-processed gelatin extraction

The objective was to characterize Nile tilapia skins, freeze- and dry salt dry-preserved to extract gelatins by batch processing. After filleting, the skins were separated from the meat and distributed into two lots: In one, skins were frozen for 7 days (-18 oC); and in the other, skins were salted for seven days (25 oC). The skins were rinsed, weighed and pretreated in H2SO4 a10N solution (pH 3.0), at a 1:6 (skin/water) ratio for 1 h at 24 oC. Gelatin was extracted in water bath at 50 oC for 1 h, and a sample was removed for molecular profiling; the rest was frozen at -18 oC. Physical-chemical analyses were carried out on the skins and liquid gelatins, the molecular profile was obtained from the gelatins, and the skins underwent microbiological analyses. Frozen and salted skins showed, respectively: 78.13% and 76.46% moisture, 18.16% and 19.59% crude protein, 2.26% and 1.90% ether extract, and 1.44% and 2.06% ash, respectively. For the liquid gelatins extracted from frozen and salted skins, moisture was 97.68% and 96.08%, crude protein was 3.18% and 4.12%, ether extract was 0.29% and 0.18%, and ash was 2.31% and 3.03%, respectively. Gel strength and viscosity values were higher for salted skins gelatin (200 g and 19.02 mPas) compared with freeze-preserved skins gelatin (12.7 g and 9.16 mPas). The molecular profile was lower in gelatin extracted from frozen skins, which indicates loss of β and γ-components, which indicates considerable collagen decay from that preservation method.