| Research Abstract |
Introduction : Muscle proteolytic enzymes, calpains and lysosomal proteases, appear to be involved in the conditioning process of meat and these proteases may enhance each other's effects. These proteases may also act on sarcoplasmic proteins, and from the results, pep tides and free amino acids were produced depend on the time of the conditioning. The amount of peptides and free amino acids are important factors in the conditioning of meat, and those improve flavor or taste of meat. In this study, the pourpous is to gain knowledge about the peptides which proteins contributed to peptides content or what components of peptides were produced.
Methods : M.Semitendinosus muscles were obtained from 8 Holstein steers 2 days after slaughter and they were prepared 3 types of beef samples : Whole muscle, Homogenate and Sarcoplasma The Homogenate sample was prepared as follows : minced meat was added into twice of 30mM citrate phosphate buffer containing 0.05% NaN_3 and 0.1 M NaCl, pH 5.5. The S
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arcoplasma was prepared as a supernatant obtained from a part of the Homogenate sample by centrifugation and then supernatant was filtered by a pore size of 0.25 mu in filter. These 3 types of beef samples were stored at 4 ﾟC until 28 days after slaughter.
In sampling on the analysis, Whole muscle was homogenized same as the preparation of the Homogenate sample and centrifuged to get the supernatant. The Homogenate was also centrifuged to get the supernatant. Each supernatant obtained from 3 beef samples were heated at 75 ﾟC for 15 mi or mixed with equal volume of 4 % TCA to removed the proteins. These 2 types of peptides fraction were named the Heat soluble peptide and the 2% TCA soluble peptides.
Results and Discussion : Peptides content was 250.7 mg/100 g beef 2 days after slaughter and was higher than that of the 2 % TCA soluble peptides. During the conditioning, peptides content increased in order to the Homogenate, Whole muscle and Sarcoplasma, and they reached to 574.3mg, 519mg and 497.8mg 28 days after slaughter, respectively. The Whole muscle and Homogenate contained myofibrillar proteins, but the Sarcoplasma was removed myofibrillar proteins. From these results, the percentage of contribution by myofibrillar proteins were 7.9% in the Whole muscle, and it were 2.3.7% in the Homogenate. These facts indicted that the increment of peptides during the conditioning was mainly originated from sarcoplasmic proteins.
Content of the 2 % TCA soluble peptides was 157.4mg 2 days after slaughter and it was about 90mg lower than that of the Heat soluble pep tides. This deference between the Heat soluble and TCA soluble was not change among the 3 types of beef samples during the conditioning. The value of 157.4 mg of the 2 % TCA soluble peptides was similar to the previous data. The values 28 days after slaughter were 412.7 mg, 486.4mg and 390.3mg in the Whole muscle. Homogenate and Sarcoplasma, respectively. These values, 486.4 mg and 390.3 mg, were higher than that of previous data. This deference may be due to the cattle of Holstein steers and Hereford steers. The peptides from myofibrillar proteins were 22.4mg and 96.1 mg in the Whole muscle and Homogenate, respectively. The percentage from it were 8.8% and 29.2% to increment peptides.
On the SDS-PAGE pattern of the Heat soluble peptides from Whole muscle, main component was 17 kDa and this was assumed as myoglobin. Another were 122 and 8.0 kDa components. During the conditioning, 42, 30, 23,14, 10.7, 7.0 and 5.5 kDa components were increased gradually.
In the results of SDS-PAGE of the Heat soluble peptides from the Sarcoplasma. The component of peptides was almost low molecular components below 17 kDa except 23 kDa. Increased components were 10.7, 8.0 and 5.5 kDa during the conditioning and main one was 8kDa. The difference between the Whole muscle and Sarcoplasma was if they contained myofibrillar proteins or not. So, it is thought that high molecular peptides, 42, 30 and 23 kDa components, were originated from niyofibrillar proteins.
Conclusion : The peptides increased during the conditioning were mainly originated from sarcoplasmic proteins, and the ratio contribution to produce peptides were 76.3- 92.1% in the Heat soluble peptides. The peptides from myofibrillar proteins was high molecular peptides, 42, 30 and 23 kDa components and the peptides from sarcoplasmic proteins were low molecular, mainly 8.0 and 5.5 kDa component. Less
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