JIA-2018-09

2122 ZHANG Yi-min et al. Journal of Integrative Agriculture 2018, 17(9): 2118–2125 enzyme due to the higher rigor temperature, which is consistent with the current study. However, the hypothesis that the increased activity of the reducing enzymes early post-mortem would deplete the reducing capacity of the meat during storage resulting in higher accumulation of MetMb and decreased colour stability (Ledward 1985), was not found in this study. This is because the MRA of SC- treated meat was still higher ( P <0.05) and the percentage of surface MetMb was lower than RC steaks on 14 d; maybe the differences would disappear with extended storage time. 3.3. Proteomics and relationships with color Eleven protein spots were identified to be differentially abundant between SC- and RC-treated beef steaks (Fig. 1), of which both spots 0719 and 1640 were identified as alpha- aminoadipic semialdehyde dehydrogenase (ALDH7A1), while spots 2116 and 3108 were identified as heat shock protein, alpha-crystallin-related, B6 (HSPB6); therefore, nine proteins were identified to be differentially abundant between the two chilling methods. Of these, ribonuclease/angiogenin inhibitor 1 (RNH1), ALDH7A1, acireductone dioxygenase 1 (ADI1), pyruvate dehydrogenase E1 component subunit beta (PDHB), and HSPB6 were over-abundant in SC- treated samples, whereas FK506 binding protein 4 (FKBP4), adenosine kinase (ADK), adenylate kinase 1 (AK1) and peroxiredoxin 1 (PRDX1) were over-abundant in RC steaks (Table 3). Regression analysis results showed the percentage variance in colour traits which each identified protein marker accounted for when the analysis was conducted on an individual basis. Proteins PDHB, FKBP4 and PRDX 1 were the top three proteins accounting for the variance (Table 4). The PCA results of the score plots showed that 99.76% of the variability of L*, a* or MetMb was explained by the first principal components, composed of PDHB, FKBP4 and PRDX1, which can distinguish the SC and RC samples. ALDH7A1 belongs to the aldehyde dehydrogenase family. It is an important cellular osmolyte and methyl donor, mediating important protective effects with multifunction, i.e., it protects cells from oxidative stress mainly by metabolizing a number of lipid peroxidation-derived aldehydes. This enzyme is also involved in the subpathway that synthesizes betaine from betaine aldehyde, which results in an accumulation of NADH. ALDH7A1 was also detected by Sayd et al . (2006), and was named as antiquitin, being highly expressed in pig semimembranosus muscles showing light color. ADI1, belongs to the acireductone Table 3 Differentially abundant sarcoplasmic proteins in beef longissimus lumborum steaks applied by step or control chilling Spot 1) Access number Identified proteins Theoretical pI/MW (kDa) 2) Sequence coverage(%) Mascot score Over- abundant 3) Fold change Function 0719 gi|187960116 Alpha-aminoadipic semialdehyde dehydrogenase (ALDH7A1) 6.69/59.115 10 237 SC 1.8 4) Oxidoreductase activity 1130 gi|73586832 Acireductone dioxygenase 1 (ADI1) 5.03/21.442 14 88 SC 6.4 4) Oxidoreductase activity 1309 gi|116242689 Pyruvate dehydrogenase E1 component subunit beta (PDHB) 6.21/39.443 18 272 SC 1.7 4) Oxidoreductase activity 1604 gi|296485604 Alpha-aminoadipic semialdehyde dehydrogenase (ALDH7A1) 6.69/59.129 23 430 SC 1.9 4) Oxidoreductase activity 2116 gi|119224088 Heat shock protein, alpha- crystallin-related, B6 (HSPB6) 5.95/17.525 37 257 SC 1.8 4) Chaperone binding 3108 gi|109939807 Heat shock protein, alpha- crystallin-related, B6 (HSPB6) 5.95/17.515 22 145 SC 1.9 4) Chaperone binding 0509 gi|74268096 Ribonuclease/angiogenin inhibitor 1 (RNH1) 4.64/50.472 23 561 SC 2.3 4) Stress related protein 2514 gi|109658154 Adenosine kinase (ADK) 5.85/38.898 30 226 RC 2.0 5) Metabolic 3106 gi|59858267 Adenylate kinase 1 (AK1) 8.40/21.764 61 381 RC 2.5 5) Metabolic 9208 gi|59858511 Peroxiredoxin 1 (PRDX1) 8.59/22.423 35 381 RC 2.2 5) Thioredoxin peroxidase activity 1714 gi|74354621 FK506 binding protein 4 (FKBP4) 5.31/51.839 2 61 RC 5.7 5) Heat shock protein binding 1) Spot refers to the numbered spots in the gel image (Fig. 1). 2) MW, molecular weight. 3) SC, step-chilling; RC, routine chilling. 4) Spot ratio of SC/RC. 5) Spot ratio of RC/SC.