Dynamic changes of bacteria and screening of potential spoilage markers of lamb in aerobic and vacuum packaging.

Microorganisms proliferate, consume nutrients, and produce many undesired metabolites, which are the main reason for the spoilage of fresh meat. Screening spoilage markers is of great significance for characterizing the freshness of fresh meat. At present, there are few studies on the volatile spoilage markers (VSMs) of lamb and their relationship with bacteria. In this study, the spoilage evolution of lamb was evaluated by multiple indicators. The changes of bacteria and volatile organic compounds (VOCs) in aerobic-packaged (AP) and vacuum-packaged (VP) lamb were measured by 16S next-generation sequencing (NGS) and headspace solid-phase microextraction (HS-SPME)-gas chromatography-mass spectrometry (GC-MS) respectively. The potential VSMs were also screened. Results showed that the shelf life of AP lamb at 4 °C was less than 10 d and VP lamb was less than 28 d. Pseudomonas was the dominant bacteria in AP lamb, while Latilactobacillus and Lactococcus were the dominant bacteria in VP lamb. Several VOCs could be recommended as potential spoilage markers, including 1-octen-3-ol, 1-hexanol, nonanal, methoxy-phenyloxime, 2,3-octanedione, acetoin and 1-pentanol for AP lamb; acetoin, 1-hexanol, 2,3-octanedione, hexanoic acid, 1-octen-3-ol, nonanal, hexanal and 2,3-octanediol for VP lamb. This study can provide information for characterizing and predicting the freshness of fresh lamb.

Sarcoplasmic and myofibrillar phosphoproteins profile of beef M. longissimus thoracis with different pHu at different days postmortem.

BACKGROUND: The abnormal ultimate pH (pHu ) in postmortem muscles affect the meat quality and results in substantial economic losses. Dark, firm, and dry (DFD) meat linked with the higher postmortem pHu values and exhibited many quality issues such as dark color, tough texture and shorter shelf life. This research aimed to investigate the effect of protein phosphorylation on variations in beef pHu in order to explore the possible mechanisms underlying DFD meat formation. RESULTS: Glycogen and lactate contents were higher, while L* and a* were lower in high pHu beef. Shear force was higher in intermediate pHu group. Global phosphorylation of sarcoplasmic proteins was higher in low pHu samples on day 1 and of myofibrillar proteins was higher in intermediate pHu meat on days 1 and 2 postmortem. Sarcoplasmic protein bands with different phosphorylation levels were identified as containing some glycometabolism and stress response proteins and phosphorylated myofibrillar protein bands were identified sarcomeric and metabolic proteins. CONCLUSIONS: Phosphorylation of multiple proteins of glycolytic pathway and contractile machinery may play critical roles in development of DFD beef. © 2021 Society of Chemical Industry.

Effects of protein posttranslational modifications on meat quality: A review.

Meat quality plays an important role in the purchase decision of consumers, affecting producers and retailers. The formation mechanisms determining meat quality are intricate, as several endogenous and exogenous factors contribute during antemortem and postmortem periods. Abundant research has been performed on meat quality; however, unexpected variation in meat quality remains an issue in the meat industry. Protein posttranslational modifications (PTMs) regulate structures and functions of proteins in living tissues, and recent reports confirmed their importance in meat quality. The objective of this review was to provide a summary of the research on the effects of PTMs on meat quality. The effects of four common PTMs, namely, protein phosphorylation, acetylation, S-nitrosylation, and ubiquitination, on meat quality were discussed, with emphasis on the effects of protein phosphorylation on meat tenderness, color, and water holding capacity. The mechanisms and factors that may affect the function of protein phosphorylation are also discussed. The current research confirms that meat quality traits are regulated by multiple PTMs. Cross talk between different PTMs and interactions of PTMs with postmortem biochemical processes need to be explored to improve our understanding on factors affecting meat quality.

Microbial and metabolic alterations in gut microbiota of sows during pregnancy and lactation.

The gut microbiota plays a critical role in various physiologic processes; however, maternal microbial and metabolic changes during pregnancy and lactation remain elusive. Using pigs as an animal model, we conducted comparative analyses of gut microbiota and short-chain fatty acid (SCFA) profiles across different stages of gestation, lactation, and the empty (nonpregnancy) phase in 2 distinct breeds of sow, Rongchang (RS) and Landrace (LS). Coriobacteriaceae were found to gradually increase over gestational time irrespective of breed, which was further validated in an independent cohort of sows, indicating that Coriobacteriaceae are likely associated with the progression of pregnancy. Escherichia increased as well. Relative to empty and gestation, lactation was associated with an increase in SCFA producers and a concomitant augmentation in SCFA production in both breeds. A comparison between the 2 breeds revealed that Ruminococcaceae were more abundant in RSs than in LSs, consistent with the strong ability of Rongchang pigs to digest highly fibrous feedstuffs. Taken together, we revealed characteristic structural and metabolic changes in maternal gut microbiota throughout pregnancy, lactation, and the empty phase, which could potentially help improve the pregnancy and lactation outcomes for both animals and humans.-Liu, H., Hou, C., Li, N., Zhang, X., Zhang, G., Yang, F., Zeng, X., Liu, Z., Qiao, S. Microbial and metabolic alterations in gut microbiota of sows during pregnancy and lactation.

Maternal milk and fecal microbes guide the spatiotemporal development of mucosa-associated microbiota and barrier function in the porcine neonatal gut.

BACKGROUND: The early-life microbiota exerts a profound and lifelong impact on host health. Longitudinal studies in humans have been informative but are mostly based on the analysis of fecal samples and cannot shed direct light on the early development of mucosa-associated intestinal microbiota and its impact on GI function. Using piglets as a model for human infants, we assess here the succession of mucosa-associated microbiota across the intestinal tract in the first 35 days after birth. RESULTS: Although sharing a similar composition and predicted functional profile at birth, the mucosa-associated microbiome in the small intestine (jejunum and ileum) remained relatively stable, while that of the large intestine (cecum and colon) quickly expanded and diversified by day 35. Among detected microbial sources (milk, vagina, areolar skin, and feces of sows, farrowing crate, and incubator), maternal milk microbes were primarily responsible for the colonization of the small intestine, contributing approximately 90% bacteria throughout the first 35 days of the neonatal life. Although maternal milk microbes contributed greater than 90% bacteria to the large intestinal microbiota of neonates upon birth, their presence gradually diminished, and they were replaced by maternal fecal microbes by day 35. We found strong correlations between the relative abundance of specific mucosa-associated microbes, particularly those vertically transmitted from the mother, and the expression levels of multiple intestinal immune and barrier function genes in different segments of the intestinal tract. CONCLUSION: We revealed spatially specific trajectories of microbial colonization of the intestinal mucosa in the small and large intestines, which can be primarily attributed to the colonization by vertically transmitted maternal milk and intestinal microbes. Additionally, these maternal microbes may be involved in the establishment of intestinal immune and barrier functions in neonates. Our findings strengthen the notion that studying fecal samples alone is insufficient to fully understand the co-development of the intestinal microbiota and immune system and suggest the possibility of improving neonatal health through the manipulation of maternal microbiota.

Effects of temperature on protein phosphorylation in postmortem muscle.

BACKGROUND: Phosphorylation is one of the most important post-translational modifications. Currently, many postmortem protein phosphorylation studies in muscle have been related to meat quality such as tenderness and color stability. However, the effects of various storage temperatures (25, 15, 4 and -1.5 °C) on the phosphorylation level of protein are poorly understood. Changes in the protein phosphorylation levels in postmortem ovine muscle at various storage temperatures were determined in this study. RESULTS: The obtained data showed that pH decline rate was significantly inhibited at -1.5 °C from 12 h to 7 days postmortem (P < 0.05). The ATP consumption rate was higher at 25 °C than that at other three temperatures (P < 0.05). Analysis of the temperature, pH and ATP content revealed that the ATP content was related to the phosphorylation levels of individual protein bands. Phosphorylated myofibrillar and sarcoplasmic proteins, such as myosin binding protein C, troponin T3, myosin light chain 1, glucose-6-phosphate isomerase and pyruvate kinase, were mainly involved in glycolysis and muscle contraction. CONCLUSION: The global and specific protein phosphorylation levels can be influenced by the postmortem storage temperature of muscle. Phosphorylation of proteins was correlated with glycolysis and muscle contraction. Certain phosphorylated proteins, such as heat shock proteins, require further study to clarify their effects on meat traits. © 2019 Society of Chemical Industry.

Lactobacillus reuteri I5007 modulates tight junction protein expression in IPEC-J2 cells with LPS stimulation and in newborn piglets under normal conditions.

BACKGROUND: Tight junctions (TJs) maintain the intestinal mucosal barrier, dysfunction of which plays a vital role in the pathophysiology of a variety of gastrointestinal disorders. Previously, we have shown that L. reuteri I5007 maintained the gut epithelial barrier in newborn piglets. Here we aimed to decipher the influence of L. reuteri I5007 on tight junction (TJ) protein expression both in vivo and in vitro. RESULTS: We found that L. reuteri I5007 significantly increased the protein abundance of intestinal epithelial claudin-1, occludin and zonula occluden-1 (ZO-1) in newborn piglets (orally administrated with 6 × 10(9) CFU of L. reuteri I5007 daily for 14 days). In vitro, treatment with L. reuteri I5007 alone maintained the transepithelial electrical resistance (TEER) of IPEC-J2 cells with time. In addition, IPEC-J2 cells were stimulated with 1 µg/mL lipopolysaccharide (LPS) for 1, 4, 8, 12 or 24 h, following pre-treatment with L. reuteri I5007 or its culture supernatant for 2 h. The results showed that LPS time-dependently induced (significantly after 4 or 8 h) the expression of TNF-α and IL-6, and decreased TJ proteins, which was reversed by pre-treatment of L. reuteri I5007 or its culture supernatant. CONCLUSIONS: L. reuteri I5007 had beneficial effects on the expression of TJ proteins in newborn piglets and the in-vitro results showed this strain had a positive effect on TEER of cells and inhibited the reduction of TJ proteins expression induced by LPS. These findings indicated L. reuteri I5007 may have potential roles in protection TJ proteins in TJ-deficient conditions.

Dietary Sodium Butyrate Decreases Postweaning Diarrhea by Modulating Intestinal Permeability and Changing the Bacterial Communities in Weaned Piglets.

BACKGROUND: The vast majority of substances used as alternatives to antibiotics produce inconsistent results and rarely equal the effectiveness of in-feed antibiotics. OBJECTIVE: This study evaluated the effects of the combined use of sodium butyrate (SB) and reduced antibiotics in a piglet diet in promoting performance and to control weaning diarrhea. METHODS: Piglets weaned at 28 d were randomly assigned to a corn-soybean meal control ration [negative control (NC)]; a similar ration with 50 mg kitasamycin/kg, 20 mg colistin sulfate/kg, and 1000 mg encapsulated SB/kg [reduced antibiotics + SB (ASB)]; or to a ration with 100 mg kitasamycin/kg and 40 mg colistin sulfate/kg [positive control (PC)] for 28 d. Performance, diarrhea incidence, intestinal permeability, and changes in the bacterial communities in the ileum and colon were determined. RESULTS: Weight gain and the ratio of weight gain to feed intake were significantly greater in the ASB and PC piglets than in the NC piglets (P < 0.05). Diarrhea incidence was lower in the ASB and PC piglets than in the NC piglets (P < 0.05). Urinary lactulose to mannitol ratios were 25% and 30% lower, respectively, whereas jejunal and colonic occludin protein expressions were significantly greater in the ASB and PC piglets compared with the NC piglets (P < 0.05). In the intestinal mucosa, malondialdehyde was lower in the ASB and PC piglets (by 42% and 43%, respectively), whereas tumor necrosis factor α (TNF-α) was 63% lower in the ASB piglets and 59% lower in the PC piglets compared with the NC piglets (P < 0.05). 16S ribosomal RNA gene sequence analysis revealed a higher colonic Shannon index and a lower colonic Simpson index in the ASB and PC piglets than in the NC piglets. In addition, the ASB and PC treatments caused a striking decrease in Lactobacillaceae and a noticeable increase in Clostridiaceae in the ileal and colonic lumen, as well as increases in Ruminococcaceae, Lachnospiraceae, and Bacteroidetes in the colonic lumen. CONCLUSION: Collectively, our results support an important role for SB in improving performance and decreasing diarrhea incidence in weaned piglets by modulation of intestinal permeability and the bacterial communities in the ileum and colon.

Comparative effects of phosphorylation and acetylation on glycolysis and myofibrillar proteins degradation in postmortem muscle.

The study investigated the different effects between protein phosphorylation and acetylation on glycolytic enzyme activity and myofibrillar protein degradation. Lamb longissimus thoracis lumborum muscles were homogenized and then inhibitors were added for incubation at 4 °C. Phosphatase inhibitor was added to produce a high phosphorylation level (PI group) and lysine deacetylase inhibitor was added to produce a high acetylation level (DI group). The lactate and ATP content in the PI group was inhibited compared with that in the DI group (P < 0.05). Phosphofructokinase (PFK) activity was negatively related with the phosphorylation level and was positively related with the acetylation level in the DI group (P < 0.05). The degradation of troponin T and desmin of the DI group were restrained when compared to that in the PI group (P < 0.05). Compared with initial PFK and desmin, the simulation of phosphorylation and acetylation of PFK and desmin showed different electrostatic potential at the surface and a more unstable structure. The phosphorylation level of the DI group was increased, suggesting that the changes of protein acetylation altered protein phosphorylation. In conclusion, compared with protein phosphorylation, protein acetylation had a greater effect on promoting glycolysis and inhibiting protein degradation.

Effects of different electrostatic field intensities assisted controlled freezing point storage on water holding capacity of fresh meat during the early postmortem period.

In this study, the effect of different intensity electrostatic fields on the water holding capacity (WHC) of fresh meat during the early postmortem period in controlled freezing point storage (CFPS) were investigated. Significantly lower cooking loss were found in low voltage electrostatic field (LVEF) and high voltage electrostatic field (HVEF) compared to the control group (CK) (p < 0.05). The myofibril fragmentation index and microstructure results suggested that the sample under HVEF treatment remained relatively intact. It has been revealed that the changes in actomyosin properties under electrostatic field treatment groups were due to the combination and dissociation of actomyosin binding into myofilament concentration, which consequently affects the muscle WHC. The study further demonstrated that the electrostatic field, especially HVEF, might increase the WHC of fresh meat by affecting the distribution of water molecules and physiochemical properties of actomyosin during the early postmortem period.

The effect of modified atmosphere packaging at an early postmortem stage on lamb meat quality during subsequent aging.

This study explores the influence of modified atmosphere packaging (MAP) on fresh lamb meat quality with respect to gas concentration, rigor state, and post-mortem aging time. A comparison was done for the quality characteristics of lamb Longissimus thoracis lumborum chops that had been packaged separately in air, 75%O2  + 25%CO2 MAP or 50%O2  + 50%CO2 MAP at 1, 6, and 24 h post-mortem and then stored for 6, 12, 24, 72, and 144 h post-mortem, and the quality of lamb chops had been evaluated at each post-mortem period separately. Chops packaged at 1 and 6 h post-mortem in MAP had reduced pH decline, less purge loss, and enhanced redness at early post-mortem storage times. Lamb color stability was evidently greater in 75%O2  + 25%CO2 MAP than in 50%O2  + 50%CO2 MAP during the early storage period when a* and R630/R580 were taken into account. Shear force values were lowest in lambs packaged at 1 h post-mortem with 75%O2  + 25%CO2 MAP at 12 h post-mortem and then increased until 72 h post-mortem, suggesting that rigor has been delayed by such a high O2 MAP. Thus, fresh lamb quality was maintained most effectively when packaged at 1 h post-mortem in 75%O2  + 25%CO2 MAP for consumption at 12 h post-mortem. The exact mechanisms and optimization of MAP based on Chinese retail conditions should be considered in future studies. PRACTICAL APPLICATION: In this study, three slaughter patterns in the meat industry involving boning immediately after dressing (hot-boning) and chilling for a short period (warm-boning) or overnight (cold-boning) are considered, as well as the behavior of non-immediate consumption after purchase. Modified atmosphere packaging provides an effective preservation of early post-mortem muscles with enhanced color stability, water holding capacity, and texture during refrigerated storage. This could provide new insights into how to process lamb muscles in the early post-mortem period to improve and stabilize lamb quality.

Effects of Different Na+ Concentrations on cAMP-Dependent Protein Kinase Activity in Postmortem Meat.

cAMP-dependent protein kinase (PKA) activity regulates protein phosphorylation, with Na+ playing a crucial role in PKA activity. The aim of this study was to investigate the effects of different Na+ concentrations on PKA activity and protein phosphorylation level in postmortem muscle. The study consisted of two experiments: (1) NaCl of 0, 20, 100, 200 and 400 mM was added to a muscle homogenate incubation model to analyze the effect of Na+ concentration on PKA activity, and (2) the same concentrations were added to pure PKA in vitro incubation models at 4 °C to verify the effect of Na+ on PKA activity. The PKA activity of the muscle homogenate model increased with storage time in groups with different Na+ concentrations. High concentrations of Na+ inhibited sarcoplasmic protein phosphorylation. The PKA activity at 24 h of storage and the sarcoplasmic protein phosphorylation level at 12 h of storage in the group with 200 mM Na+ was lower than that of the other groups. After 1 h incubation, the PKA activity of samples in the 200 mM Na+ group was inhibited and lower than that in the other Na+ groups in the in vitro incubation model. These results suggest that the Na+ concentration at 200 mM could better inhibit PKA activity. This study provided valuable insights for enhancing curing efficiency and improving meat quality.

Contribution of mono- and co-culture of Pseudomonas paralactis, Acinetobacter MN21 and Stenotrophomonas maltophilia to the spoilage of chill-stored lamb.

Exploring the contribution of common microorganisms to spoilage is of great significance in inhibiting spoilage in lamb. This work investigated the extent of protein degradation and profile changes of free amino acids (FAAs), free fatty acids (FFAs) and volatile organic compounds (VOCs) in lamb caused by single- and co-culture of the common aerobic spoilage bacteria, P. paralactis, Ac. MN21 and S. maltophilia. Meanwhile, some key VOCs produced by the three bacteria during lamb spoilage were also screened by orthogonal partial least square discriminant analysis and difference value in VOCs content between inoculated groups and sterile group. Lamb inoculated with P. paralactis had the higher total viable counts, pH, total volatile base nitrogen and TCA-soluble peptides than those with the other two bacteria. Some FAAs and FFAs could be uniquely degraded by P. paralactis but not Ac. MN21 and S. maltophilia, such as Arg, Glu, C15:0, C18:0 and C18:1n9t. Co-culture of the three bacteria significantly promoted the overall spoilage, including bacterial growth, proteolysis and lipolysis. Key VOCs produced by P. paralactis were 2, 3-octanedione, those by Ac. MN21 were 1-octanol, octanal, hexanoic acid, 1-pentanol and hexanoic acid methyl ester, and that by S. maltophilia were hexanoic acid. The production of extensive key-VOCs was significantly and negatively correlated with C20:0, C23:0 and C18:ln9t degradation. This study can provide a basis for inhibiting common spoilage bacteria and promoting high-quality processing of fresh lamb.

Acetylation and Phosphorylation Regulate the Role of Pyruvate Kinase as a Glycolytic Enzyme or a Protein Kinase in Lamb.

Protein post-translational modifications (PTMs) play an essential role in meat quality development. However, the effect of specific PTM sites on meat proteins has not been investigated yet. The characteristics of pyruvate kinase M (PKM) were found to exhibit a close correlation with final meat quality, and thus, serine 99 (S99) and lysine 137 (K137) in PKM were mutated to study their effect on PKM function. The structural and functional properties of five lamb PKM variants, including wild-type PKM (wtPKM), PKM_S99D (S99 phosphorylation), PKM_S99A (PKM S99 dephosphorylation), PKM_K137Q (PKM K137 acetylation), and PKM_K137R (PKM K137 deacetylation), were evaluated. The results showed that the secondary structure, tertiary structure, and polymer formation were affected among different PKM variants. In addition, the glycolytic activity of PKM_K137Q was decreased because of its weakened binding with phosphoenolpyruvate. In the PKM_K137R variant, the actin phosphorylation level exhibited a decrease, suggesting a low kinase activity of PKM_K137R. The results of molecular simulation showed a 42% reduction in the interface area between PKM_K137R and actin, in contrast to wtPKM and actin. These findings are significant for revealing the mechanism of how PTMs regulate PKM function and provide a theoretical foundation for the development of precise meat quality preservation technology.

Zein and tannic acid hybrid particles improving physical stability, controlled release properties, and antimicrobial activity of cinnamon essential oil loaded Pickering emulsions.

Pickering emulsion loading essential oil has demonstrated a promising strategy as delivery system in food preservation, but localization in stability and antimicrobial activity limits application. In this study, Pickering emulsions co-loaded with tannic acid and cinnamon essential oil (ZTC) have been developed based on zein and tannic acid complexes (ZT) mediated interfacial engineering. Fourier transform infrared, fluorescence spectroscopy, and molecular docking results indicated tannic acid altered the structural of zein. Interfacial tension results indicated that tannic acid accelerated the adsorbed speed of zein particles by decreased interfacial tension (11.99-9.96 mN/m). ZT5 formed a viscoelastic and dense layer in oil-water interface than that for other ZTs, which improved stability and control release performance of ZTC. Furthermore, the ZTC showed an effective antimicrobial activity against spoilage organisms Pseudomonad paralactis MN10 and Lactobacillus sakei VMR17. These findings provide new insight for developing co-loaded multiple antimicrobial agents within Pickering emulsion as a delivery system.

Effects of different cold chain logistics modes on the quality and bacterial community succession of fresh pork.

The connection and temperature control of cold chain links are key to ensuring meat quality. Considering the practical production of cold chain logistics in China, this study investigated the impact of various cold chain logistics modes (including warehousing, transportation, and sales conditions) at different temperature settings (7 °C, 4 °C, and - 1 °C), modeled in the laboratory, on the quality and bacterial community succession of pork. The pork quality was evaluated by pH, water holding capacity, total volatile basic nitrogen (TVB-N), total viable count (TVC) and myowater status. Among the different cold chain logistics modes, the LL1 (samples being warehoused and transported at 4 °C for 96 h and sold at -1 °C) and the SL1 (samples being warehoused and transported at 4 °C for 30 h and sold at -1 °C) modes were suitable for inter-provincial and intra-provincial transportation due to their long shelf life (> 14 days), respectively. The bacterial community succession of pork in different cold chain logistics modes was accessed by high-throughput sequencing. The results indicated that the cold chain logistics modes had affected the bacterial community, with Latilactobacillus being the dominant bacteria in the LL1 mode and SL1 mode during spoilage. The study revealed that the entire or partial process supercooling treatment (-1 °C) during the cold chain logistics process could effectively preserve the meat quality, supporting the high-quality development of the fresh meat cold chain logistics.

Expression of catalase in Lactobacillus fermentum and evaluation of its anti-oxidative properties in a dextran sodium sulfate induced mouse colitis model.

Lactic acid bacteria are generally sensitive to hydrogen peroxide (H2O2). Lactobacillus plantarum ATCC14431 is one of the few lactic acid bacteria able to degrade H2O2 through the action of a manganese-dependent catalase (containing the katA gene). However, it is not a natural inhabitant of the intestinal tract and its bio-efficacy and survival in the gastrointestinal tract have never been tested. In this study, we successfully expressed the katA gene from L. plantarum ATCC14431 in L. fermentum I5007 and the recombinant L. fermentum exhibited almost 20-fold higher catalase activity than the empty vector control. The anti-oxidative properties of this catalase-producing L. fermentum were evaluated using a dextran sodium sulphate (DSS) induced colitis mice model. Compared with the control, mice receiving DSS alone had increased diarrhea and mucosa histological scores (P < 0.05), as well as lipid peroxidation (P < 0.05), myeloperoxidase (P < 0.05), and active NF-κB in colonic tissue (P < 0.05). Similar to vitamin E, treatment with recombinant L. fermentum mitigate these effects accompanied by a improvement in mucosa histological scores in the proximal colon (P < 0.05) and decreased lipid peroxidation (P < 0.05), myeloperoxidase (P < 0.05) and active NF-κB in colonic tissue (P < 0.05). In conclusion, the expression of catalase in L. fermentum increased its ability to survive when exposed to aerated environment in vitro and conferred the anti-oxidative and anti-inflammatory effects in the DSS induced colitis model.

Changes in water holding capacity of chilled fresh pork in controlled freezing-point storage assisted by different modes of electrostatic field action.

Electrostatic field-assisted low-temperature preservation is considered a novel technology, which provides an effective means of extending the shelf-life of meat. This study aimed to investigate the effects of different output time modes of a high voltage electrostatic field (HVEF) on the water holding capacity (WHC) of chilled fresh pork during controlled freezing-point storage. Under a direct current HVEF generator, chilled fresh pork samples were treated by the single, interval, or continuous HVEF treatment, with a control check group receiving no HVEF treatment. It was determined that the WHC of the continuous HVEF treatment higher than the control check group. This difference was proven by analyzing the moisture content, storage loss, centrifugal loss, cooking loss, and nuclear magnetic resonance imaging. Furthermore, the mechanism behind HVEF-assisted controlled freezing-point storage reduced the moisture loss was conducted by examining the changes in the hydration characteristics of myofibrillar protein. The study revealed that myofibrillar proteins exhibit high solubility and low surface hydrophobicity under continuous HVEF. Additionally, continuous HVEF has been demonstrated to effectively maintain the higher WHC and lower hardness of myofibrillar protein gel by inhibiting the water molecule migration. The demonstration of these results showcases the effectiveness of electrostatic fields for the future physical preservation of meat.

Phosphorylation of Calpastatin Negatively Regulates the Activity of Calpain.

Tenderness is an important characteristic of meat quality. Calpastatin and calpain play important roles in meat tenderization. However, it is not clear how phosphorylation affects the regulation of calpastatin on µ-calpain and, consequently, meat tenderness. Calpastatin with high and low phosphorylation levels were obtained in vitro corresponding to the treatments by protein kinase A (PKA) and alkaline phosphatase. Then, calpain was incubated with calpastatin with different phosphorylation levels, and the effect of calpastatin on calpain activity under different phosphorylation levels was analyzed. The results showed that PKA promoted the phosphorylation of calpastatin, and a high phosphorylation level was maintained during incubation. The degradation rate of µ-calpain in AP group was higher than that in the other groups, meaning there was lower inhibition of calpastatin on calpain activity. The degradation of calpastatin was lower and its structure was more stable after phosphorylation. One more serine 133 site of calpastatin was identified in PKA group compared with the other groups. Phosphorylation at serine 133 of calpastatin enhanced its inhibition on calpain activity by maintaining its structural stability, thus inhibiting the tenderization of meat.

Development of Plastic/Gelatin Bilayer Active Packaging Film with Antibacterial and Water-Absorbing Functions for Lamb Preservation.

In order to extend the shelf life of refrigerating raw lamb by inhibiting the growth of microorganisms, preventing the oxidation of fat and protein, and absorbing the juice outflow of lamb during storage, an active packaging system based on plastic/gelatin bilayer film with essential oil was developed in this study. Three kinds of petroleum-derived plastic films, oriented polypropylene (OPP), polyethylene terephthalate, and polyethylene, were coated with gelatin to make bilayer films for lamb preservation. The results showed significant improvement in the mechanical properties, oxygen, moisture, and light barriers of the bilayer films compared to the gelatin film. The OPP/gelatin bilayer film was selected for further experiments because of its highest acceptance by panelists. If the amount of juice outflow was less than 350% of the mass of the gelatin layer, it was difficult for the gelatin film to separate from lamb. With the increase in essential oil concentration, the water absorption capacity decreased. The OPP/gelatin bilayer films with 20% mustard or 10% oregano essential oils inhibited the growth of bacteria in lamb and displayed better mechanical properties. Essential oil decreased the brightness and light transmittance of the bilayer films and made the film yellow. In conclusion, our results suggested that the active packaging system based on OPP/gelatin bilayer film was more suitable for raw lamb preservation than single-layer gelatin film or petroleum-derived plastic film, but need further study, including minimizing the amount of essential oil, enhancing the mechanical strength of the gelatin film after water absorption.