This study aimed to clarify the changes in ATPase activity and its effect on the microstructure and water-holding capacity (WHC) of Tan sheep meat during postmortem aging. The Longissimus dorsi muscle of Tan sheep slaughtered at 6 months of age was aged at 4 ℃ and evaluated for the activities of Na⁺-K⁺-ATPase, Ca²⁺-ATPase and caspase-3, microstructure, pH and drip loss rate after 0, 1, 2, 4 and 8 days. Results showed that the activities of Na⁺-K⁺-ATPase and Ca²⁺-ATPase increased initially and subsequently decreased with aging time, peaking at day 1. The activity of caspase-3 and drip loss increased with aging time up to 2 days and then decreased. In contrast, the opposite trend was observed for muscle pH. The contents of total proteins, low-salt soluble proteins, and high-salt soluble proteins continuously decreased with aging time. The content of water soluble proteins significantly decreased after day 2 (P < 0.05). On day 8, the myofibrils were broken, and gaps between myofibers, between muscle fiber bundles, and between myofibers and sarcolemma appeared; the Z lines were broken, and the H bands disappeared. Correlation analysis indicated that the activity of Na⁺-K⁺-ATPase was correlated with all other parameters (P < 0.01) and the activity of Ca²⁺-ATPase was significantly correlated with muscle pH and the activities of Na⁺-K⁺-ATPase and caspase-3 (P < 0.01). Overall, during postmortem aging, the variations in the activities of Na⁺-K⁺-ATPase and Ca²⁺-ATPase can lead to downstream caspase-3 activation to hydrolyze cytoskeleton proteins, resulting in the formation of gaps at different muscle sites. The water in muscle flows into the formed gaps due to gravity, causing an increase in the drip loss and a decrease in the WHC of Tan sheep meat.

In order to reveal the mechanisms underlying the change in the water-holding capacity of Tan sheep meat during postmortem chilled storage, the pH, cooking loss and centrifugal loss of Longissimus dorsi muscle from six-month-old Tan sheep were measured at 0, 4 and 8 days of chilled storage. Using proteomics based on isobaric tags for relative and absolute quantification (iTRAQ), the level of protein expression in Tan sheep meat was investigated. The results showed that the pH decreased significantly and then increased slightly with chilling time. The cooking loss and centrifugal loss increased continuously. Proteomic analysis showed that tropomyosin 2 (TPM2), myosin light chain 1 (MYL1), troponin I2 (TNNI2), troponin C2 (TNNC2), troponin T3 (TNNT3), myosin light chain 2 (MYL2), actinin α3 (ACTN3), actin (cytoplasmic 1) (ACTB), actin α1 (ACTA1), and actinin α2 (ACTN2) were identified as core differential abundant proteins. TPM2, MYL1, TNNI2, TNNC2, TNNT3, MYL2 and ACTN2 were up-regulated at 0 versus 4 days and down-regulated at 4 versus 8 days; ACTB and ACTA1 were down-regulated at 0 versus 4 days and up-regulated at 4 versus 8 days. ACTN3 was continuously up-regulated from day 0 to day 8. These proteins, located in the sarcomere, the muscle fibers and the cell membrane, could participate in the regulation of muscle contraction and ATPase activity by binding to cytoskeletal proteins or ions during postmortem aging, thereby leading to muscle contraction and changes in muscle structure, finally affecting the water retention of Tan sheep meat. Muscle pH had significant effects on ACTB, ACTA1, MYL1, TNNC2, TNNT3, ACTN2, TPM2 and TNNI2. Muscle pH as well as MYL1, ACTA1 and ACTN3 had significant effects on the cooking loss. MYL2 and ACTN3 had important effects on the centrifugal loss.

This study was designed to clarify the changes in the expression level of hypoxia-inducible factor 1 (HIF-1) and its effects on the activity of triose-phosphate isomerase (TPI), the contents of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP), and meat quality traits in Tan sheep meat during a 48-hours postmortem aging period. Results indicated that the expression level of HIF-1 increased significantly between 2 and 24 h, and then decreased. The activity of TPI increased significantly, reaching a maximum value at 6 h, then significantly decreased until 48 h. The contents of ATP, ADP, and AMP significantly decreased with increasing aging time, while muscle pH significantly decreased (P < 0.05). The color values of L*, a*, and b* were significantly increased with increasing aging time. Correlation analysis indicated that the expression level of HIF-1 was correlated with meat quality indicators, TPI activity, and the contents of ATP, ADP and AMP significantly (P < 0.05, P < 0.01). It might be speculated that postmortem hypoxia could induce a rapid increase in the expression level of HIF-1 within 6 h postmortem, and the transfer of the HIF-1 complex to the nucleus to bind with glycolytic genes, thereby promoting the expression of glycolysis-related genes, enhancing postmortem glycolysis, leading to increased activity of glycolysis-related enzymes and decreased muscle pH. To sum up, HIF-1 can affect meat color by regulating postmortem muscle glycolysis and pH.

In this study, liver DNA from purebred Ningxia Tan sheep, purebred Xinjiang fine-wool sheep and purebred Tibetan sheep was extracted followed by genomic library construction, amplification, purification and quality control. Simple sequence repeat (SSR) sites in the sequence were detected, and 50 pairs of primers were designed, synthesized and screened for polymerase chain reaction (PCR) amplification. SSR typing was carried out by capillary electrophoresis, and polymorphic primers were selected to detect the genetic polymorphism of the three breeds. The results showed that 10 pairs of SSR primers successfully amplified stable bands. Ten pairs of polymorphic SSR primers were used to analyze the genetic diversity of Ningxia Tan sheep, Xinjiang fine-wool sheep and Tibetan sheep, showing an average number of alleles (Na) of 4.100, 3.100 and 3.600, average number of effective alleles (Ne) of 3.782, 2.747 and 3.193, average observed heterozygosity (Ho) of 1.007, 1.009 and 0.953, average expected heterozygosity (He) of 0.704, 0.615 and 0.660, and average polymorphic information content (PIC) of 0.432, 0.414 and 0.425, respectively. These data indicated that the genetic polymorphism of Ningxia Tan sheep was higher than that of Tibetan sheep and Xinjiang fine-wool sheep. The results of capillary electrophoresis with fluorescence detection showed that the fluorescent primers scaffold632:150-463, scaffold31384:146-461 and scaffold7676:103-270 had excellent specificity for Ningxia Tan, Xinjiang fine-wool and Tibetan sheep, respectively, and they could effectively distinguish the breeds. In conclusion, the gene banks established can allow scientific and accurate identification of Ningxia Tan sheep, Tibetan sheep and Xinjiang Fine-wool sheep.

The changes of volatile odor substances in chilled Tan sheep meat stored for different periods (0, 2, 4, 6, 8 and 10 days) at 0-4 ℃ and cooked in boiling water were investigated using solid phase micro-extraction (SPME) combined with gas chromatography-mass spectrometry (GC-MS) and an electronic nose system. In total, 38 volatile compounds were detected, including 19 aldehydes, 11 alcohols, 4 ketones, 3 acids and 1 heterocyclic compound. More specifically, the numbers of volatile compounds identified from meat samples stored for 0, 2, 4, 6, 8, and 10 days were 24, 26, 30, 32, 31 and 29, respectively, showing a trend of first increasing and then decreasing with storage period. The key aroma components in cooked meat were identified by relative odor activity value (ROAV). Among them, hexanal, octanal, heptanal, (E)-2-octenal, nonanal, benzaldehyde, 1-pentanol, 1-hexanol, 1-octene-3-ol, and 2-pentyl furan were common to all six samples with aldehydes being the predominant ones, contributing a lot to the flavor of cooked Tan sheep meat. The ROAV of aldehydes increased initially and then decreased, reaching the highest level on the 4th day. The results of the electronic nose showed that cooked four-day stored meat had greater odor intensity and better flavor.

Roast Tan sheep (an indigenous breed in Yanchi County, Ningxia Hui Autonomous Region) meat adulterated with duck meat and pure roast sheep meat were discriminated by an electronic nose. Their volatile composition was analyzed by headspace solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) and chemometrics. The results showed that a total of 53 volatile compounds were identified in five adulterated samples, including 12 alcohols, 15 aldehydes, 3 acids, 2 esters, 8 ketones, 8 alkanes, 1 heterocyclic compound and 4 other compounds. Principal component analysis (PCA) clearly distinguished the electronic nose data for the overall odor of adulterated roast mutton samples, and showed that the major differential volatile compounds were alcohol compounds. By partial least squares discriminant analysis (PLS-DA), five characteristic volatile substances were found in adulterated samples, namely 1-octanol, 1-pentanol, hexanal, acetic acid, and dodecane, which will be useful to determine the level of duck meat in adulterated roast mutton samples.

In this study, the contents of 25 mineral elements in Tan sheep bone samples from Etuokeqian banner of Inner Mongolia autonomous region, Yanchi county of Ningxia autonomous region, Huan county of Gansu province and Dingbian county of Shaanxi province were determined by inductively coupled plasma-mass spectrometry (ICP-MS). The results showed that the distribution characteristics of bone mineral elements in Tan sheep from different regions were different, and the contents of some mineral elements were significantly different among different geographical origins. In addition, through principal component analysis (PCA), cluster analysis (CA), Ca, Cd, Cd, Mg, Mn, Na, P, Rb, Te, and Zn were selected to develop a fingerprint for tracing the geographical origin of Tan sheep. The overall accuracy rates of back substitution test and cross-validation were 87.50% and 86.87%, respectively. The results showed that the 10 mineral elements were effective for identification of the regional origin of Tan sheep bones, and the discriminant model established by using the 10 elements was also effective.

Moisture distribution and migration in the tallow of Tan sheep from Yanchi, Ningxia roasted for different periods were analyzed by low field-nuclear magnetic resonance (LF-NMR). Head space solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and an electronic nose (E-Nose) were used to analyze the volatile components of mutton tallow. The results showed that the L^* value of mutton tallow decreased, and the a^* and b^* values increased with roasting time. The percentage of weakly bound water showed an increasing trend, and the percentage of immobile water showed a decreasing trend. The relaxation time T₂₃ showed a significantly decreasing trend with roasting time, indicating tighter binding of water molecules to macromolecular substances. A total of 78 volatile compounds were detected in 10 samples, including 12 aldehydes, 11 alcohols, 9 ketones, 4 alkanes, 10 acids, 12 esters, 12 heterocyclic compounds and 8 other compounds, with hexanal, nonanal, 1-octene-3-ol, 3-hydroxy-2-butanone, 7-methyl-3-methylene-1,6-octadiene and toluene being the major ones. Esters were found mainly in the early stage of roasting, while heterocyclic compounds, especially pyrazine compounds, mainly in the late stage. Principal component analysis performed on E-nose data showed that different roasting periods had significant effects on the contents of nitrogen oxides, benzenes, organic sulfur compounds and alcohols in mutton tallow, but little effect on alkanes, hydrides and ammonia compounds.

To investigate the influence of freezing rate on the volatile flavor compounds in hand-grab mutton, the differences in the volatile flavor compounds among unfrozen samples (control) and those frozen at three different freezing rates, namely 0.26 (-18 ℃), 0.56 (-40 ℃) and 2.00 cm/h (-80 ℃) were analyzed by headspace solid phase micro-extraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) and electronic nose. The results showed that the eutectic point temperature of hand-grab mutton was (-9.66 ± 0.24) ℃. In terms of overall odor perception, the electronic nose could distinguish hand grab mutton frozen at different freezing rates. Totally 44, 40, 49 and 53 volatile substances were identified in the control, -18 ℃ frozen, -40 ℃ frozen and -80 ℃ frozen samples, respectively, among which aldehydes, alcohols and ketones were the major ones. The content of total volatile substances in these frozen samples was 30.78%, 40.79% and 70.75% of that in the control group, respectively. The contents of aldehydes, alcohols, ketones, acids and esters decreased with decreasing freezing rate. For all samples, hexanal, heptanal, octanal, nonanal, (E)-2-octenal, 2,4-decadienal and 1-octen-3-ol were determined as key aroma compounds based on relative odor activity value (ROAV). The higher the freezing rate, the greater the ROAV values of these compounds. The sensory scores of the four samples followed the decreasing order of control > -80 ℃ > -40 ℃ > -18 ℃ (P < 0.05). In summary, we concluded that the freezing of hand-grab mutton can cause losses of a large number of volatile aroma components, but higher freezing rates can reduce the loss of volatile aroma components, maintaining the original flavor to a large extent.

The moisture distribution and key volatile flavor compounds of beef tallow from Qinchuan cattle roasted for different periods were analyzed by low field-nuclear magnetic resonance (LF-NMR) spectroscopy and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed that the L* value significantly decreased (P < 0.05), the a* and b* values first increased and then decreased with roasting time. The proportion of bound water in beef tallow did not change significantly (P > 0.05), while the proportion of immobile water first increased and then decreased, and the proportion of free water showed an overall downward trend (P > 0.05). The relaxation time T₂₃ and T₂₄ showed a significant decreasing trend as roasting time increased (P < 0.05), indicating that the binding between water molecules and macromolecular substances such as protein and lipid became tighter. Beef tallow samples roasted for different periods could be effectively distinguished by electronic nose and the roasting process had a significant effect on the contents of alcohols, aromatic compounds, terpenes, and organic sulfur compounds in beef tallow according to principal component analysis (PCA) of the electronic nose data. A total of 95 volatile compounds were identified in all samples. The contents of 1-methoxy-2-propanol, 1-octene-3-ol, hexanal, nonanal, acetic acid, nonanoic acid, and acetamide were relatively higher in each sample, whereas ketones, heterocycles and amine compounds occurred mostly in the later stages of roasting. In total 19 key aroma components were identified based on odor activity value (OAV) and most of the substances have the largest OAV at 12 min of roasting.