Pigmentation Of Commercial Cold-Smoked Atlantic Salmon During Processing And Retil Display
The pink color of the flesh of Atlantic salmon is highly favored by consumers and is therefore an important quality parameter. However, there is considerable evidence that undesirable color changes occur in Atlantic salmon fillets during processing into a cold-smoked product and during subsequent storage. As astaxanthin is considered to r be responsible for the pink color of Atlantic salmon flesh, this color change may be expected to be due to the oxidative degradation of this carotene. This project was designed to examine this color change and changes to astaxanthin and other components of the fish flesh which may be involved in such oxidation reactions. The other components included the anti-oxidative vitamins a-tocopherol and ascorbic acid, moisture, lipid (total and individual fatty acids) as well as lipid oxidation products as measured by thiobarbituric acid-reactive substances (TBARS). The interrelationships among these components and between these components and measures of color were examined in order to identify the causes of the color change during processing and storage. The changes in the fillets were investigated in 3 experiments: in Experiments 1 and 2, both fresh and previously frozen fish were used whereas in Experiment 3 only fresh fish were used. For Experiments I and 2, conducted in August 2002, samples of Tasmanian Atlantic salmon (Salmon salar) stored frozen since harvest in February 2002 (designated as “frozen”) together with fresh fish harvested at that time (designated as "fresh") from Tasmanian salmon farms were used. Fillets from both frozen and fresh fish were used in order to ascertain whether prior freezing affected the extent of color and other changes in the flesh during processing and subsequent storage. For Experiment 3, fresh fish harvested in January 2004 were used without being frozen. In Experiment 1, the color attributes of salmon flesh were examined during standard commercial processing practices from ‘raw’ (A) to ‘washed’ (B) to ‘salted’ (C) to cold ‘smoked’ (D) fillets. Flesh color at each step was recorded objectively using a Minolta Chromatometer and the color of raw fillets was measured subjectively using warranted investigation. Considerable oxidation occurred in cold-smoked salmon between the end of Experiment 1 (sample D) and day 0 of the retail display in Experiment 2 (sample E); this led to Experiment 3 being conducted. Processing practices in the factories changed while this project was being conducted, so that in Experiment 3 one of the processing steps examined in Experiment I, washing (B) was not applied. Samples examined were: ‘raw’ (A), ‘salted’ (C), cold-‘smoked’ stored chilled for 3 days (D!), cold-smoked stored chilled for 7 days (D2) and cold-smoked stored chilled for 10 days (E), equivalent to retail display day O. In Experiment 3, the instrumental color score, especially redness, decreased significantly during processing, confirming the discoloration found in Experiment 1. The lack of a washing step in Experiment 3 did not appear to affect the concentrations of astaxanthin, a-tocopherol, lipid and TBARS in smoked salmon (D), but did appear to affect ascorbic acid and moisture contents. The only significant interactions found in this experiment were between a-tocopherol and astaxanthin, and between utocopherol and lipid immediately after smoking (D). The results indicate that cold smoking of Atlantic salmon fillets has a significant effect on surface color, regardless of the application of a washing process step. Astaxanthin concentrations were stable throughout processing, subsequent chilled storage prior to marketing of cold-smoked salmon and during retail display. Alphatocopherol, total lipid and percentage of individual fatty acids, including EPA and DHA appeared to remain constant in the experiments conducted. Processing followed by chilled storage in unpackaged form significantly increased the oxidation status (TEARS value), and decreased ascorbic acid concentration and moisture content. However, the TEARS level, moisture and ascorbic acid contents generally remained constant during retail display for 28 days. In most cases, there was similarity in the patterns of component changes of frozen and fresh fillets, suggesting that the effect of processing is greater than the effect of freezing. It is concluded that the change of color during the standard commercial processing steps and following chilled storage resulted from changes on the surface of the flesh only. The changes in the instrumental color measurements, especially redness (a* 06001564
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