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Background: Oxidation of myoglobin is responsible for the undesirable appearance and loss in acceptability of fish and fish products. The retardation of such a change by a modification of the surrounding atmosphere would be a means to maintain the quality of fish during the refrigerated storage., Results: The changes in oxymyoglobin and metmyoglobin from dark muscle of Eastern little tuna (Euthynnus affinis) as affected by different atmospheric systems (closed system, opened system and flushed oxygen system) were determined. A saturated oxygen atmosphere more likely weakened the haem-globin complex, especially as the exposure time increased. Autoxidation of the oxy form proceeded rapidly in the presence of oxygen with the concomitant formation of the met form. When the oxygen was excluded, oxidation of oxymyoglobin was retarded. With flushed oxygen and increasing exposure time, conformational changes of globin occurred, mainly associated with protein oxidation. Generally, oxymyoglobin was more susceptible to oxidation and conformational change than did metmyoglobin. After keeping the samples at 4 °C for 3 days, dark muscle of tuna fillet kept in vacuum packaging had a slight decrease in redness and it was still acceptable. The fillets stored in exposed air or packed in 100% O(2) atmosphere turned brown, most likely due to myoglobin oxidation., Conclusion: The oxygen level of the packaging atmosphere had a profound impact on myoglobin alteration, which was governed by the forms of myoglobin., (Copyright © 2011 Society of Chemical Industry.)

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., (Copyright (c) 2009 Society of Chemical Industry.)