Relationship of postmortem troponin-T degradation and meat tenderness of beef Longissimus dorsi from different production systems in Thailand

Troponin-T degradation in relationship to tenderness of beef Longissimus dorsi (LD) from four different production systems had been observed. LD muscles from natural grass grazed native Thai cattle (N, 100%, Bos indicus, n=10), straw and grass-fed with 3-mo concentrate finish Brahman crossbred (BG, 100% Bos indicus, n=10), pineapple by product-fed with 6-mo concentrate finished Brahman crossbred (BP, 100% Bos indicus, n=10), and at least 50% Bos taurus of Charolais crossbred steers with 12 to 18-mo concentrate finishing (C, n=5), were vacuum aged (4°C) over aging period of 1, 7 and 14 days. The 30 kDa band (SDS– PAGE) corresponding to the troponin-T degradation were detectable and increased in intensity with increasing ageing period, with the most intense BP, followed by N, BG and C, respectively. However, the 37 kDa band was not found the in C group compared to the indicus cattle at 14 days of ageing. The average means of WB shear force values were 3.96, 13.61, 9.52 and 13.76 kg in C, BG, BP and N beef, respectively. Introduction It is well known that the tenderness of meat depends on several factors such as breed, production systems, feed, storage of carcasses, connective tissue content and myofibrillar protein degradation, etc. Thai beef has a great difference in meat quality especially tenderness. More than 95% of beef in Thailand are from indicus cattle which had not been aged prior to sale. Storage of carcasses at refrigerated temperature has been reported to improve the tenderness by increasing myofibrillar protein degradation (Koohmaraie and Shackelford, 1991). The degradation of myofibrillar proteins such as titin, desmin and troponin-T (Tn-T) have shown to play a role in the development in meat tenderness (Huff-Lonergan et al., 1996). One of the most common symptoms of protein degradation during aging is appearance of Tn-T degradation products having molecular weight about 30-kDa (Joo et al., 1999). A 30-kDa polypeptide was detected in several bovine muscles postmortem at the same time that Tn-T was decreasing (Ho et al., 1997) and Steen et al. (1997) found 80% of Tn-T degradation between day 1 and 8. The objectives of this study were to investigate Tn-T degradation products (30-kDa) of beef LD muscle from different breeds and production systems during 1, 7 and 14-days postmortem in cold storage and to determine tenderness of meat (Warner-Bratzler shear force) during ageing period and relate to the intensity of 30-kDa polypeptide . Materials and methods Beef LD muscle from four production systems in Thailand, natural grass grazed native Thai cattle (N; 100% Bos indicus, 214-kg, n=10), straw and grass-fed with 3-mo concentrate finished Brahman crossbred (BG; 100% Bos indicus, 487-kg, n=10), pineapple byproducts-fed with 6-mo concentrate finished Brahman crossbred (BP; 100% Bos indicus, 497-kg, n=10), and at least 50% Charolais crossbred steers, with 12 to 18mo concentrate finishing (C, 664-kg, n=5). Samples were taken from the 6 to the 12 ribs of the abdominal region at 24 hours postmortem. Steaks of 2.5cm thickness were vacuum-packaged and aged at 4C for 1, 7 and 14 days. The pH, Warner-Bratzler shear force (WBSF) and SDS-PAGE analysis were determined. The pH value was measured at 24 hr postmortem 7 and 14 days by pH Meter model WTW (Germany) and Electrode-WTW pH-sentix. The WBSF values was measured by Instron Warner–Bratzler Model 1011 with 50 kg compression load cell and speed 500 mm/min (Devine et al., 1999), the. Myofibrillar protein extraction and SDS-PAGE analysis were performed using the method reported by Clayes et al. (1995). SeeBlue® Plus2 Pre-Stained Standard (Invitrogen) was used as protein molecular weight marker. Bovine serum albumin (BSA) was used as an internal control for relative quantitative measurement of Tn-T and 30 kDa protein band. The data of pH, WBSF and 30-kDa were statistically determined according to 4x3 factorial arrangement in completely randomized design which factor A was 4 different breeds and production systems and factor B was 3 different ageing periods.