The spawning migration of chum salmon results in a deterioration of the eating quality of the flesh. There is a loss in the colour of the muscle from red-pink to white-grey, a distinct off-flavour develops and the firm texture becomes soft and watery. The reduced appeal of the canned and fresh product results in an economic loss of this important B.C. commodity.
Chum salmon were sampled at four stages during their spawning migration in order to describe the physical, chemical and structural changes which occurred as the fish matured. The fish were categorized into four grades based on their external characteristics. Grade one, silver-brights, were the least mature fish, grade two, intermediates, and grade three, darks, were progressively more mature. Grade four, spawning, were the most mature. Proximate analysis of the raw muscle revealed a significant decrease in protein and lipid and increase in moisture. The level of astaxanthin and the Hunter values a/L, a and a/b decreased significantly with increasing grade.
The texture of the canned fish was measured instrumentally with an Instron Universal Testing Machine using the texture profile analysis (TPA) method. A panel of semi-trained judges also evaluated the canned flesh based on its firmness, fibrousness, dryness, and chewiness. The sensory panel determined that the silver-bright fish were significantly more firm, fibrous, dry, and chewy than the spawning fish. Of the ten instrumental TPA parameters, cohesiveness and slope 2 were able to distinguish between grade one and four. Poor correlation between the instrumental and sensory measure of texture suggested that the softening characterized by the sensory panel was not being measured by the Instron.
Thin and ultrathin sections of the muscle were photographed at the light and electron microscopic level. The light micrographs clearly showed an apparent loss in the myofibrillar diameter or number within muscle fibres as the fish became more mature. Focal degeneration of myofibrils was evident in the electron micrographs. Changes were described by four criteria, smearing, the loss of a distinct appearance of the actin and myosin, splitting, the tearing of myofibril bundles, thinning, a loss in myosin or actin filaments, and an increase in intermyofibril space.
Proteinase activity of the dorsal muscle was assayed at pH 3.5, 6.2 and 7.0. There was a significant increase in activity at pH 3.5 but no change at pH 6.2 or 7.0. Acid phosphatase, a lysosomal marker, also increased significantly with grade. These findings suggested that lysosomal enzymes largely contributed to the degradation in the muscle. / Land and Food Systems, Faculty of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/30277 |
| Date | January 1991 |
| Creators | Reid, Rebecca Anne |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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