L Uytterhaegen

Effects of double-muscling on carcass quality, beef tenderness and myofibrillar protein degradation in Belgian blue white bulls

Carcass properties and meat quality characteristics of 32 Belgian Blue White double-muscled bulls (DM) were compared with those of 59 bulls of the same breed with normal conformation (N). DM showed superior carcass quality as revealed in increased dressing percentage, meat production yield, conformation grade, muscle/fat and muscle/bone ratios (all P < 0·001). Longissimus dorsi (LD) shear force values, drip and cooking losses at 8 days post mortem (pm) were significantly higher (P < 0·001) for DM, whereas sarcomere lengths were not different. Calpain 1 and calpastatin levels at 1 h and 24 h pm were tremendously decreased in DM as were also cathepsin B and L levels at 1 and 8 days pm (P < 0·001). As evident from semi-quantitative SDS-PAGE, these differences were accompanied by higher titin and lower 30 kDa levels (P < 0·001) in DM. Troponin-t levels were not different, but very low. Intramuscular collagen content was significantly lower in DM (P < 0·001). This suggests that lower background toughness in DM was compensated for by reduced post-mortem proteolytic tenderization. Discrepancy with literature reports regarding tenderness of DM might be related to the extreme muscularity of the Belgian Blue White breed, compared to other DM breeds. The results also suggest that reduced protein turnover might be involved in the muscle hypertrophy phenomenon within this breed, because of likely reduced levels of calpains and cathepsins in living DM animals.

Quantification of beef myofibrillar proteins by SDS-PAGE

A semi-quantitative determination of beef myofibrillar proteins using sodium, dodecyl sulphate polyacrylamide gel electrophoresis is described. Bovine serum albumin was used as internal standard. Results indicate a linear relationship between densitometric readings after staining with Coomassie brilliant blue R(250) and protein content. Recoveries of four pure proteins, loaded within a range of 0·5-4 μg, were between 92 and 110%. Heating of beef myofibrillar protein samples during dissolution is shown to be unnecessary. The method allows the quantitative study of myofibrillar degradation during beef aging, without overlapping of troponin-T with tropomyosin bands.

Effect of dietary energy and protein levels on fatty acid composition of intramuscular fat in double-muscled Belgian Blue bulls

Seventy six Belgian Blue (BB) bulls, with double-muscled conformation, were randomly allocated to six dietary treatments in a 2 × 3 factorial experiment. The treatments included low (N(L)=127 g CP/kg DM), medium (N(M)=153 g CP/kg DM) and high (N(H)=172 g CP/kg DM) levels of dietary protein in combination with low (E(L)=7.38 MJ ME/kg DM) and high (E(H)=8.03 MJ ME/kg DM) levels of dietary energy. Fatty acid composition was determined on total lipid samples of the M. longissimus thoracis of all animals and on the separated triacylglycerol and polar lipid fatty acid fractions of the medium-protein group. Dietary energy and protein levels influenced the carcass characteristics of BB bulls but the effects were small. Carcass fat cover score, carcass fat content and intramuscular fat content were slightly but significantly higher in the animals on the high versus the low energy diets. The overall intramuscular fat content was very low (<1%) and the overall polyunsaturated:saturated fatty acid ratio (0.39) high compared to normal figures for beef. The high versus the low dietary energy level increased the monounsaturated (P<0.001) and decreased the polyunsaturated (P<0.001) fatty acid proportion with no change in the saturated fatty acid proportion. This may have been due in part to the addition of beef tallow to increase the energy level of the diet. Concomitant shifts in the individual fatty acids included increased proportions of C14:0 (P<0.001), C16:0 (P<0.03), C16:1 (P<0.01), C18:1 (P<0.001) and decreased proportions of C18:2 (P<0.001) and C20:4 (P<0.001). Increasing dietary protein levels had inconsistent effects on the fatty acid profiles. The proportion of polar lipid fatty acids in the total fatty acids was 0.34 and 0.25 for the E(L) and E(H) group, respectively, in the Nm treatment group. Changes in fatty acid proportions of the triacylglycerol fatty acid fraction were similar to those seen in the total lipid fatty acids when related to dietary energy level, but no significant changes in the polar lipid fatty acid proportions were observed. Significant linear relationships were found between measures of carcass and muscle fatness and fatty acid proportions. With increasing muscle total fatty acid content, saturated and monounsaturated fatty acid proportions increased (r=0.38 and r=0.55, respectively, P<0.01) and the polyunsaturated fatty acid proportion decreased (r=-0.73, P<0.01). The diet had some effects but the relatively unsaturated intramuscular fatty acid composition was mainly related to the low total fat content of the BB animals.

The effect of electrical stimulation on beef tenderness, protease activity and myofibrillar protein fragmentation

From six one-year-old White red bulls, one randomly assigned carcass half was subjected to high voltage electrical stimulation (HVES) at 1 h post morten (pm). Longissimus dorsi (LD) steaks from control (C) and stimulated sides (ES) were removed at 24 h pm, stored at 4 degrees C and sampled at 1, 6, 8 and 12 days pm. HVES caused an immediate fall of pH with about 0.5 units (P less than 0.01), and an increase in temperature of about 1 degree C (P less than 0.05). HVES lowered LD shear force values (P less than 0.05), both at 1 and 8 days pm. Sarcomere length was not affected by stimulation, but cooking losses were increased in ES. Semi-quantitative SDS-PAGE, using BSA as internal standard showed the rate of degradation of several myofibrillar proteins to be increased by HVES. Levels of 43-kDa peptide increased upon ageing and were higher in ES (P less than 0.001). The level of 30-kDa peptide increases strongly in the early ageing period and faster in ES. It is striking that 1 h pm ES contain more 30 kDa (P less than 0.05), suggesting activation of calpain 1. The increase upon ageing in levels of 34- and 35-kDa peptides, often considered as the tropomyosins, suggests that these compounds are myofibrillar degradation products. Troponin-T (TNT) was degraded very fast in the early ageing period. The degradation rate was increased by HVES (P less than 0.005) and related to rate of tenderization (r = 0.90).(ABSTRACT TRUNCATED AT 250 WORDS)

Early post-mortem conditions and the calpain/calpastatin system in relation to tenderness of double-muscled beef

Early post mortem temperature, pH, sarcomere length, colour, water holding capacity, calpain/calpastatin activities and myofibrillar protein concentrations (semi-quantative SDS-PAGE), measured at different times post mortem on 153 double-muscled Belgian Blue White bulls, were related to shear force (SF) measurements. The M. longissimus thoracis tenderised up to 8 days post mortem. SF was slightly correlated with temperature at 3 h post mortem (r = 0.20, p = 0.015), but not with pH early post mortem. Higher ultimate pH values measured at 24 h post mortem were related to darker meat, lower cooking losses and shorter sarcomere lengths. Sarcomere length was significantly related to SF, even after 12 days of ageing, suggesting that proteolytic activity was not able to overcome shortening. Up to 12 days post mortem, calpastatin and m-calpain activities were significantly correlated with SF suggesting a considerable role of calpains in meat tenderization of double-muscled Belgian Blue White bulls, although at 24 h post mortem, μ-calpain could no longer be detected. Titin, nebulin, filamin and troponin-T were degraded during the ageing period. Troponin-T was degraded by 80% between day 1 and 8. At 8 days post mortem its concentration was significantly correlated with 30 kDa (r = 0.63, p = 0.00), shear force (r = 0.39, p = 0.00), calpastatin activity at 1 day post mortem (r = 0.29, p = 0.01) and with the m-calpain/ calpastatin activity ratio at 1 day post mortem (r = -0.43, p = 0.00).