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Extraction and characterisation of pepsin-solubilised collagens from the skin of bigeye snapper (Priacanthus tayenus and Priacanthus macracanthus).

BACKGROUND
Fish collagen has been paid increasing attention as an alternative to the mammalian counterpart owing to the abundance of fish skin as a processing by-product. Generally, the low yield of collagen extracted using the typical acid solubilisation process has led to the use of mammalian pepsin as an aid for increasing the yield. Alternatively, fish pepsin, especially from tuna stomach, can be used for the extraction of pepsin-solubilised collagen (PSC). Therefore the objective of this study was to extract and characterise PSC from the skin of bigeye snapper, a fish widely used for surimi production in Thailand.


RESULTS
PSCs from the skin of two species of bigeye snapper, Priacanthus tayenus and Priacanthus macracanthus, were extracted with the aid of tongol tuna (Thunnus tonggol) pepsin and porcine pepsin. PSCs from the skin of both species extracted using porcine pepsin had a higher content of beta-chain but a lower content of alpha-chains compared with those extracted using tuna pepsin. All PSCs contained glycine as the major amino acid and had an imino acid (proline and hydroxyproline) content of 189-193 residues per 1000 residues. Transition temperatures of PSCs were in the range 30.6-31.3 degrees C. Fourier transform infrared spectra revealed some differences in molecular order between PSCs extracted using porcine pepsin and tuna pepsin. Nevertheless, the triple-helical structure of PSCs was not affected by pepsin digestion. Zeta potential analysis indicated that PSCs from P. tayens and P. macracanthus possessed zero net charge at pH 7.15-7.46 and 5.97-6.44 respectively.


CONCLUSION
Tongol tuna pepsin could be used as a replacement for mammalian pepsin in PSC extraction. However, a slight difference in PSC properties was found.