Changes in the Quality of Chicken Breast Meat due to Superchilling and Temperature Fluctuations during Storage.

The aim of this study was to determine the changes in chicken breast meat quality (water-holding capacity, color, texture, myofibrillar fragmentation index (MFI), total protein solubility, thiobarbituric acid reactive substances (TBARS), total viable count (TVC), and lactic acid bacteria (LAB) count) due to storage under superchilling conditions (-1.3°C) and fluctuating temperatures (ranging from -20°C to -5°C) as compared to the quality of meat stored at chilled (2-4°C) and frozen (-20°C) temperatures, respectively. Results indicated that the TVC and LAB count of the chilled and superchilled breast meat increased with storage time. TVC of the chilled and superchilled breast meat reached the safety level of 7 log cfu/g at approximately day 8 and18, respectively. This suggested that the superchilling method extended the storage duration by 10 days. Weight loss and TBARS of the chilled and superchilled samples tended to increase with increasing storage time. The color, texture, protein solubility, and MFI were stable throughout the entire storage period of the chilled (9 days) and superchilled (28 days) samples. Results indicated that while three cycles of storage temperature fluctuation influenced the weight loss and dry matter of the meat, they did not affect the TVC, LAB count, texture, color, pH, MFI, and protein solubility. The superchilling technique (-1.3°C) could extend the shelf-life of meat and maintain the quality of chicken breast meat. Fluctuations in temperature during frozen storage decreased the water-holding capacity of chicken breast meat, indicating that temperature stability should be maintained during frozen storage.

Proteolysis in pork loins during superchilling and regular chilling storage.

This study aimed to address the proteolytic phenomena taking place in pork loins during prolonged storage at superchilling (SC) temperature. Loins were stored at either chilling (CH) conditions (2-4 °C) for 4 weeks or at SC temperature (around -1 °C) for 12 weeks. Storage at SC temperatures slowed down the rate of proteolysis in pork loins, so that final levels of most indicators for proteolysis, including after 12 weeks of SC storage were similar to those after 4 weeks at CH conditions. Consequently, the texture of SC pork under extended storage was not so different to that of CH pork. However, total amino acid content peaked by the end of SC storage, pointing out to a potential ongoing exopeptidase activity. Overall, proteolysis seemed to be slowed down in pork at SC conditions, with similar levels for most indicators after 12 weeks of SC storage or 4 weeks at CH conditions.

Oxidative deterioration of pork during superchilling storage.

BACKGROUND: In superchilling (SC), meat is kept at temperatures around 1 °C below its initial freezing point, leading to a significant increase in shelf life. This study aimed to address the oxidative changes taking place in pork loins during prolonged storage at SC temperature. Loins were stored either at chilling (CH) conditions (2-4 °C) for 4 weeks or at SC temperature (around -1 °C) for 12 weeks. RESULTS: Storage at SC temperature diminished the rate of lipid and protein oxidation and discoloration in pork loins, so that final levels of most oxidation products and instrumental color values after 12 weeks of SC storage were similar to those after 4 weeks at CH conditions. However, hexanal content peaked by the end of SC storage, pointing to a potential accumulation of compounds from lipid oxidation during SC storage. CONCLUSION: SC storage of pork slows down the rate of lipid and protein oxidation. However, accumulation of volatile compounds from lipid oxidation could be a limiting factor for shelf life. © 2017 Society of Chemical Industry.

The effect of temperature on the activity of µ- and m-calpain and calpastatin during post-mortem storage of porcine longissimus muscle.

The experiment was conducted to determine the effect of temperature during post-mortem muscle storage on the activity of the calpain system, the myofibril fragmentation and the free calcium concentration. Porcine longissimus muscle were incubated from 2h post-mortem at temperatures of 2, 15, 25 and 30 °C and sampling times were at 2, 6, 24, 48 and 120 h post-mortem. After 120 h at 30 °C the free calcium concentration increased to 530 µM from 440 µM at 2 °C. Incubation at temperatures higher than 2 °C resulted in the appearance of autolyzed m-calpain activity and a decrease of native m-calpain activity. Native m-calpain decreased more slowly than native µ-calpain, and the autolysis process started later. Myofibril fragmentation increased with storage time and incubation temperature, while calpastatin activity decreased. The study showed that high temperature incubation not only rapidly activated µ-calpain but at higher temperatures and later time points also m-calpain.

Gel-based phosphoproteomics analysis of sarcoplasmic proteins in postmortem porcine muscle with pH decline rate and time differences.

Meat quality development is highly influenced by the pH decline caused by the postmortem (PM) glycolysis. Protein phosphorylation is an important mechanism in regulating the activity of glycometabolic enzymes. Here, a gel-based phosphoproteomic study was performed to analyze the protein phosphorylation in sarcoplasmic proteins from three groups of pigs with different pH decline rates from PM 1 to 24 h. Globally, the fast pH decline group had the highest phosphorylation level at PM 1 h, but lowest at 24 h, whereas the slow pH decline group showed the reverse case. The same pattern was also observed in most individual bands in 1-DE. The protein phosphorylation levels of 12 bands were significantly affected by the synergy effects of pH and time (p<0.05). Protein identification revealed that most of the phosphoproteins were glycometabolism-related enzymes, and the others were involved in stress response, phosphocreatine metabolism, and other functions. The phosphorylation of pyruvate kinase and triosephosphate isomerase-1 showed to be related to PM muscle pH decline rate. Our work sheds light on the potential role of protein phosphorylation on regulating meat quality development.

Desmin and troponin T are degraded faster in type IIb muscle fibers than in type I fibers during postmortem aging of porcine muscle.

A novel approach was applied in this study to directly evaluate the effect of muscle fiber type on postmortem protein degradation. Porcine muscle fibers were isolated from longissimus muscle at day 1, 3, and 6 postmortem. Fibers were sorted by immunochemical myosin heavy chain isoform typing. Western blot analysis of fibers pooled separately into type I or IIb showed that the relative amounts of 39- and 50-kDa desmin degradation fragments at day 6, and 28- to 31-kDa fragments of troponin T fast type isoform (fTnT) at day 1 and 6 postmortem were higher in type IIb than in type I fibers. At day 6 troponin T slow type isoform (sTnT) was less degraded than fTnT in type I fibers. These results indicated greater rate and extent of proteolysis in type IIb than in type I fibers and higher susceptibility of fTnT to proteolysis than that of sTnT isoform.

Influence of early pH decline on calpain activity in porcine muscle.

This study investigated the influence of post-mortem pH decline on calpain activity and myofibrillar degradation. From 80 pigs, 30 Longissimus dorsi (LD) muscles were selected on the basis of pH values at 3h post-mortem and classified into groups of 10 as fast, intermediate and slow pH decline. The rate of pH decline early post-mortem differed between the three groups, but the ultimate pH values were similar at 24h. Calpain activity and autolysis from 1 to 72h post-mortem were determined using casein zymography and studied in relation to myofibrillar fragmentation. Colour and drip loss were measured. A faster decrease in pH resulted in reduced level of mu-calpain activity and increased autolysis of the enzyme, and hence an earlier loss of activity due to activation of mu-calpain in muscles with a fast pH decline. Paralleling the mu-calpain activation in muscles with a fast pH decline a higher myofibril fragmentation at 24h post-mortem was observed, which was no longer evident in the later phase of the tenderization process. In conclusion, the rate of early pH decline influenced mu-calpain activity and the rate but not the extent of myofibrillar degradation, suggesting an early effect of proteolysis on myofibril fragmentation that is reduced during ageing due to an earlier exhaustion of mu-calpain activity.

Evidence for post-mortem m-calpain autolysis in porcine muscle.

The objective of the present work was to characterize changes in calpain activity in pork post-mortem. Samples from pig M. longissimus dorsi and M. semimembranosus were collected three days post-mortem from 75 animals and analyzed with casein zymography. The results indicated post-mortem autolysis of m-calpain as two m-calpain bands were observed on the zymogram gel. Use of M. longissimus dorsi from three pigs collected at different times during storage further confirmed post-mortem autolysis of m-calpain. The activity of the autolyzed form of m-calpain was detectable at day 3 and further increased at day 6. The results also showed a decrease in the non-autolyzed m-calpain activity during post-mortem storage. Collectively, these results suggest that m-calpain is active post-mortem in porcine muscles.