Colour changes in tuna during canning and colour improvement by chemical modification of haeme proteins

Abstract

SummaryA significant loss in tristimulus colour values of precooked tuna during canning was observed and the loss was greatest in albacore followed by skipjack and then yellowfin. In terms of CIE chromaticity values, precooked albacore showed a large gain in y and, in particular, x after canning; yellowfin showed a large increase in x, slight increase in y, and large decrease in z after canning; skipjack showed a large increase in y and x, and a large decrease in z. The greater the amount of reducing sugar in the raw fish, the darker the colour of the canned product. Addition of cysteine and homocysteine before cooking caused lightening of the colour of a heated aqueous extract of soluble proteins; cysteine and trimethylamine oxide (TMAO) caused greening, which was prevented by the addition of anti‐oxidants; homocysteine and TMAO not only improved the colour but also prevented greening. Similar effects were observed in intact tuna loin muscle. Economically, it is valuable to be able to forecast the colour of a canned product before it is packed.