Study On Quality Evaluation And Improvement Of Fresh Pork

The quality of fresh pork meat is a complicated and multipleunit character. Studies on its intrinsic mechanism, evaluation and management are always the hottest research fields of the meat science. Such kinds of researches have been generally focused on lean rates and differences in the quality between normal and poor meat (such as PSE). However, studies on why or how different species or feed modes especially in intensive and fast breeding conditions influence the quality of the fresh pork have not been investigated yet. Moreover, methods for effectively evaluating the quality of the fresh pork are still not well established as far as we know.Therefore, this study was conducted to evaluate the quality of fresh pork of two different species (Jinhua pigs in the original area of Zhejiang, China (termed as JH), and hybrid pigs of Duroc×Landrace×Yorkshire, termed as DLY) with different feeding periods by using technologies of differential proteomics, low field nuclear magnetic resonance (NMR) and electronic tongue. Intrinsic mechanism underlying the determination of the quality was investigated by analyzing differences in protein expression profiles, moisture existence and antioxidative abilities among different fresh porks. In addition, feasible methods and approaches for improving the meat quality were also determined according to effects of preslaughter treatment on the quality of fresh pork. Results obtained in the present study not only provided evidence for understanding the intrinsic mechanism of the meat quality, but also valuable methods for quick monitor, evaluation and grade mark of meat quality under different conditions such as species, period, feed, breeding mode, animal welfare, slaughter and processing. The main results of the present study were as follows. 1. Effects of pre-slaughter treatment of creatine monohydrate and butafosfan on the quality of fresh porkCreatine monohydrate (CMH) supplemented into diet of DLY at the level of 500 g/t could effectively improve the quality of fresh pork in the present study. The results showed that eye muscle area and rate of longissimus dorsi muscle after CMH-treatment increased (p < 0.01) by 9.04% and 15.73%, respectively. The contents of crude fat, moisture, creatine, glycogen, inosinic acid, and inosine in treatment groups (12.02%, 71.02%, 41.63umol/g, 92.73mg/100g, 2.30mg/g and 0.39mg/g, respectively) were significantly increased or decreased (p < 0.01) as compared with respective ones of the control group (8.92%, 74.21%, 36.43umol/g, 85.21mg/100g, 1.78mg/g and 0.28 mg/g, respectively). Moreover, CMH-treatment caused a remarkable decrease in drip loss (p < 0.01) and a significant increase in creatine kinase activity (p < 0.01) in longissimus dorsi after 24h postmortem. As for the free fat acid and glucose concentrations and creatine kinase activity in blood serum treated with CMH, they were increased (p < 0.05) by 13.33%, 5.35% and 18.84%, respectively, as compared with that of the control.Butafosfan (T1 and T2, 150 mg/kg and 300 mg/kg by body weight, respectively) supplemented into drinking water beginning at 40-48 h of pre-slaughter (once at 8h-interval) could improve availably the influence of environment such as stress on the pork quality. Drop losses of longissimus dorsi treated with T1 and T2 were decreased (p < 0.01) by 25.10% and 26.05%, respectively, as compared with that of the control. In contrast, the contents of creatine, glycogen and creatine kinase in longissimus dorsi of both treatment groups (42.13umol/g, 93.52mg/100g and 188.36U/mg in the T1-treated group; 44.53umol/g, 99.72mg/100g, 195.63U/mg in the T2-treated group, respectively) were significantly higher than the respective one of the control (37.33umol/g, 84.79mg/100g, 157.54U/mg). 2. Differential proteomics of fresh porkThe procedure and method of differential proteomics of fresh pork were established with the pork sample preparation and experimental optimization of 2-DE. Differences in the expression profile of 345 pretein were observed between the fresh pork of JH and DLY. Among them, the profile of 33 proteins showed a significant difference as compared with their corresponding ones. Twelve points were chosen from the 33 protein points before the next measurement according to the statistical and quantity analysis and the demand of mass spectrum (MS). Then different expressed proteins were identified using the MALDI-TOF-MS and contrastively analyzed with the peptide mass fingerprinting (PMF) and MASCOT software. The results obtained from the samples prepared at 0 h indicated that there were six different proteins (predicted protein; actin chain A; hypothetical protein; EST1 and myoglobin, chain B) and an unknown protein (No. 1101) between two species of pig. As for the samples at 24 h, seven differential proteins (β-2 globin; lymphocyte antigen; SOD;β-globin; myosin regulatory; Actin-capping protein and Dj-1 with sulfinic acid) were observed. These results suggested that meat quality of porcine longissimus dorsi might be associated with these differential proteins. However, only 70% of differential proteins were identified using MALDI-TOF-TOF-MS because of the scarcity of the protein database responding to pork meat quality.3. Effect of water-holding capacity, water status and muscle antioxidation on meat qualityTransverse relaxation time (T₂) of fresh pork sampled at different postmortern time was studied using NMR under magnetic field intensity 0.5T and resonance frequency 21-23 MHz. T₂₁ representing bound water indicated that there was no significant difference in each pork meat. However, T₂₂ representing uneasy fluid of water was higher (P < 0.05) in JH meat at all postmortem time (0h, 12 h, 24 h and 36 h) than that of DLY and showed significant trend from the same species or slaughter weight. The T₂₂ of DLY was relatively low in the present study except the samples prepared at 6 h and 30 h. As for T₂₃ representing free water, similar results were observed. The data suggested that T2 could well reflect the drip loss of each period and the detailed water distribution and variety could be obtained with the T₂ subdivision. Thus, results obtained here would provide important cues for the recognition of uneasy flow water distribution in pork meat taken from different pig species.The antioxidation and specific enzyme activities of different meat samples were also determined. As a result, the antioxidative activity of JH fresh meat represented by some factors such as SOD, GSH-Px, inhibition ability of hydroxyl radical, total antioxidant capacity and free fat acid concentration was higher than that of DLY and exhibited a positive correlation with drip loss and texture. The activity of GSH-Px in JH was 6-8 times higher (p<0.05) than that of DLY. Total antioxidant capacity (TOAC) of JH was also greatly stronger than that of DLY. For example, TOAC in the meat of 60kg-JH at 0h-postmortern point showed about 6-, 4- and 3-fold higher than that of all three weight of DLY, respectively. And TOAC in the meat of 75kg- or 90kg-JH was about 5-, 4- and 3-fold higher, or 6-, 5- and 3-fold higher than that of all three weight of DLY, respectively. With regard to TOAC in the meat of DLY, it increased with the increase in the body weight. Free fat acid concentrations in the postmortern meat were greatly associated with the pig species, while they were almost not affected by the market weight. The free fat acid concentrations in JH meat were significantly higher (p < 0.05) than those of DLY meat, being more than 3-fold higher at average.The results in meat texture, pH and drip loss showed that pork hardness, chewiness and gumminess were not only associated with the market weight, but also greatly depended on pig species. However, the meat elasticity was not associated with the pig species. Higher meat hardness, chewiness and pH were observed in JH pork as compared with those in DLY pork, respectively. The variation trends of pH in JH pork were consistent with that of DLY pork based on the same market weight. The pH values in pork of both species decreased continiously from 0h to 12h postmortem and then kept unchanged almostly. Drip loss of DLY pork at each postmortem period was higher than that of JH pork and increased obviously with the slaughter weight. As for JH pork, the drip loss also increased with the slaughter weight. However, no significant difference (p > 0.05) was observed.4. Evaluation of electronic tongue on fresh pork qualityThe core technique in whole characters for identificating and evaluating postmortem pork quality was studied using the pulse electronic tongue with multi-frequency and broad width prepared previously in our laboratory. And the corresponding methods and procedures were established. The sensors array and correlated test parameters were analyzed comparatively with the different electrodes and the adaptive electrodes were manufactured by platinum, aurum, titanium, tungsten and palladium. The results indicated that the homogenate proportion of pork samples was 1:5 (g/ml) and the identification accuracy of electronic tongue was up to 85% (p < 0.05) using the blind sample analysis. Different pork samples were identified effectively when the Mahalanobis distance (d) was more than 2 based on the correlation between distance arithmetic and identification result. Moreover, the similarity to assess the fresh pork quality was designed and determined by combinations with the principal component analysis and cosine angle metric mode. Thus, the meat samples from different species and storage time were evaluated effectively using the above similarity under the standard samples and the control indexes. Moreover, these methods were also confirmed to solve the corresponding problems of meat freshness and shelf life. Based on the findings of the presnt study, the innovative approaches and methods including differential proteomics, water-holding capacity and water status were provided to discuss the intrinsic mechanism and quality evaluation of the postmortern pork characters. Furthermore, electronic tongue developed in the present study would provide one of the new methods for meat classification, label and freshness (shelf life) control under modern intensive swine production.