Type of carbohydrate in feed affects the expression of small leucine-rich proteoglycans (SLRPs), glycosaminoglycans (GAGs) and interleukins in skeletal muscle of Atlantic cod (Gadus morhua L.).

Aquaculture requires feed that ensures rapid growth and healthy fish. Higher inclusion of plant ingredients is desirable, as marine resources are limited. In this study we investigated the effects of higher starch inclusion in feed on muscular extracellular matrix and interleukin expression in farmed cod. Starch was replaced by complex fibers in the low-starch diet to keep total carbohydrate inclusion similar. Blood glucose and fructosamine levels were elevated in the high-starch group. The group fed a high-starch diet showed up-regulation on mRNA level of proteoglycans biglycan and decorin. ELISA confirmed the real-time PCR results on protein level for biglycan and also showed increase of lumican. For decorin the protein levels were decreased in the high-starch group, in contrast to real-time PCR results. Disaccharide analyses using HPLC showed reduction of glycosaminoglycans. Further, there was up-regulation of interleukin-1ß and -10 on mRNA level in muscle. This study shows that the muscular extracellular matrix composition is affected by diet, and that a high-starch diet results in increased expression of pro-inflammatory genes similar to diabetes in humans.

Changes in protein abundance between tender and tough meat from bovine longissimus thoracis muscle assessed by isobaric Tag for Relative and Absolute Quantitation (iTRAQ) and 2-dimensional gel electrophoresis analysis.

The aim of this study was to find potential biomarkers for meat tenderness in bovine Longissimus thoracis muscle and to compare results from isobaric Tag for Relative and Absolute Quantitation (iTRAQ) and 2-dimensional gel electrophoresis (2-DE) analysis. The experiment included 4 tender and 4 tough samples, based on shear force measurements at 7 d postmortem, from young Norwegian red (NRF) bulls, taken at 1 h postmortem. A number of the proteins which have previously been related to tenderness were found to change in abundance between tender and tough samples, both in iTRAQ (P < 0.1) and 2-DE analysis (P < 0.05). Furthermore, 3 proteins that have not previously been related to tenderness were found to change significantly in abundance between tender and tough meat samples in the present study. These include proteins related to control of flux through the tricarboxylate cycle [2-oxoglutarate dehydrogenase complex component E2 (OGDC-E2)], apoptosis (galectin-1) and regulatory role in the release of Ca(2+) from intracellular stores (annexin A6). Even though the overlap in significantly changing proteins was relatively low between iTRAQ and 2-DE analysis, certain proteins predicted to have the same function were found in both analyses and showed similar changes between the groups, such as structural proteins and proteins related to apoptosis and energy metabolism.

Relevance of calpain and calpastatin activity for texture in super-chilled and ice-stored Atlantic salmon (Salmo salar L.) fillets.

The aim of the present experiment was to measure the protease activities in ice-stored and super-chilled Atlantic salmon (Salmo salar) fillets, and the effect on texture. Pre-rigour fillets of Atlantic salmon were either super-chilled to a core temperature of -1.5°C or directly chilled on ice prior to 144h of ice storage. A significantly higher calpain activity was detected in the super-chilled fillets at 6h post-treatment compared to the ice-stored fillets and followed by a significant decrease below its initial level, while the calpastatin activity was significantly lower for the super-chilled fillets at all time points. The cathepsin B+L and B activities increased significantly with time post-treatment; however, no significant differences were observed at any time points between the two treatments. For the ice stored fillets, the cathepsin L activity decreased significantly from 6 to 24h post-treatment and thereafter increased significantly to 144h post-treatment. There was also a significantly lower cathepsin L activity in the super-chilled fillets at 0h post-treatment. No significant difference in breaking force was detected; however, a significant difference in maximum compression (Fmax) was detected at 24h post-treatment with lower Fmax in the super-chilled fillets. This experiment showed that super-chilling had a significant effect on the protease activities and the ATP degradation in salmon fillets. The observed difference in Fmax may be a result of these observed differences, and may indicate a softening of the super-chilled salmon muscle at 24h post-treatment.

Relationship between muscle microstructure, the calpain system, and shear force in bovine longissimus dorsi muscle.

The objective of this study was to examine the occurrence of microstructural changes in aged LM from Norwegian Red cattle, and to investigate how these changes relate to pH decline, calpain and calpastatin activities, and tenderness (Warner-Bratzler shear force; WBSF). Samples of the LM from 403 Norwegian Red dual-purpose bulls were collected over a 4-yr period and analyzed for muscle pH, protease activity, and WBSF. Microstructural analysis of fiber-fiber detachment, muscle fiber-perimysium detachment, contracted muscle fibers, and fractured muscle fibers were performed on a subset of 50 animals. The occurrence of fractured muscle fibers was negatively correlated with WBSF (r = -0.33, P < 0.05) and calpastatin activity (r = -0.51, P < 0.01) and was positively correlated with the ratio of µ-calpain:calpastatin activity (r = 0.66, P < 0.001), strongly indicating that these fractures are important in the development of meat tenderness and that they are a result of calpain-mediated proteolysis. In contrast, detachments between individual muscle fibers and between muscle fibers and the perimysium did not play an important role in determining variation in LM tenderness in these animals. Moreover, both pH decline and what is considered a normal ultimate pH range in beef were positively correlated with calpastatin activity and WBSF and were negatively correlated with fractured muscle fibers. Thus, an accelerated muscle pH decline and a low ultimate pH seem to increase calpain-mediated proteolysis, causing fractures in muscle fibers and thereby giving rise to more tender meat.

Peroxiredoxin-6--a potential protein marker for meat tenderness in bovine longissimus thoracis muscle.

The muscle sarcoplasmic proteins from bovine M. longissimus thoracis muscle were studied using proteomics to identify possible protein markers for meat tenderness. This study included 3 experiments: A1, A2, and B. From a collection of biopsies from the bovine M. longissimus thoracis muscle, excised 4 d before slaughter from 178 Norwegian Red young bulls, 26 biopsies were studied in Exp. A1. Based on Warner-Bratzler shear force (WBSF) values at 7 d postmortem, the biopsies were separated into a tender and a tough group of 13 bulls each and analyzed by 2-dimensional gel electrophoresis (2-DE) and Western blotting. The 2-DE experiments identified 4 different proteins: stress-70 protein, protein DJ-1, peroxiredoxin-6, and malate dehydrogenase, which were different in abundance in the tender and tough groups. However, only peroxiredoxin-6 was confirmed by quantification from Western blots. Peroxiredoxin-6 is an antioxidant enzyme that plays a role in protecting cells from oxidative stress. Peroxiredoxin-6 was identified through 3 spots of the same molecular weight, but with different pI on the Western blots. Only one of the spots was more abundant in the biopsies from the tender group. In Exp. A2, samples collected 1 h postmortem from the same animals and muscles as in Exp. A1 were analyzed by Western blotting. In these postmortem samples, the same spot from peroxiredoxin-6 as in Exp. A1 was more abundant in the tender group. In addition, one of the other peroxiredoxin-6 spots was also more abundant in the tender group. To verify the results from Exp. A, biopsies from 14 additional animals were analyzed in Exp. B by Western blotting against stress-70 protein, protein DJ-1, peroxiredoxin-6, and malate dehydrogenase. No significant differences between the tough and tender groups could be observed in these biopsies. However, for peroxiredoxin-6, the tendencies pointed in the same direction as in Exp. A. In conclusion, peroxiredoxin-6 might be a potential protein marker for meat tenderness detectable in biopsies and in samples collected shortly after slaughter. However, more animals are needed to verify the findings in the present study.