The effect of ageing on the water-holding capacity of pork: role of cytoskeletal proteins

Evaluation of Physicochemical Deterioration and Lipid Oxidation of Beef Muscle Affected by Freeze-thaw Cycles

This study was performed to explore the deterioration of physicochemical quality of beef hind limb during frozen storage at -20℃, affected by repeated freeze-thaw cycles. The effects of three successive freeze-thaw cycles on beef hind limb were investigated comparing with unfrozen beef muscle for 80 d by keeping at -20±1℃. The freeze-thaw cycles were subjected to three thawing methods and carried out to select the best one on the basis of deterioration of physicochemical properties of beef. As the number of repeated freeze-thaw cycles increased, drip loss decreased and water holding capacity (WHC) increased (p<0.05) till two cycles and then decreased. Cooking loss increased in cycle one and three but decreased in cycle two. Moreover, drip loss, WHC and cooking loss affected (p<0.05) by thawing methods within the cycles. However, pH value decreased (p<0.05), but peroxide value (p<0.05), free fatty acids value (p<0.05) and TBARS value increased (p<0.05) significantly as the number of repeated freeze-thaw cycles increased. Moreover, significant (p<0.05) interactive effects were found among the thawing methods and repeated cycles. As a result, freeze-thaw cycles affected the physicochemical quality of beef muscle, causing the degradation of its quality.

Aging implications on fresh muscle traits of Certified Angus Beef steaks

Vacuum-packaged Certified Angus Beef (CAB) subprimals ( = 72) that included the longissimus thoracis (LT), longissimus lumborum (LL), gluteus medius (GM), and infraspinatus (IF) muscles were purchased from a major beef packing facility. Subprimals were allocated to 1 of 3 aging periods (14, 28, or 42 d) and aged at 2°C. After aging, 5 steaks were cut from each subprimal and assigned to pH, water-holding capacity, Warner-Bratzler shear force (WBSF), cooked color, cooking yield, cooking loss, and sensory panel analysis. Infraspinatus steaks were more tender ( < 0.05) than all other steaks, and subprimals aged 14 d had greater ( < 0.05) WBSF values than the other 2 aging periods, regardless of muscle. Water-holding capacity and cook yield were greater ( < 0.05) for LL and LT than IF and GM steaks, whereas purge loss was greater ( < 0.05) for IF and GM than LL and LT steaks. Throughout the aging periods, pH declined for all muscle groups, with IF steaks having the greatest ( < 0.05) pH values among all muscles. Among IF steaks, sensory evaluations of all attributes did not ( ≥ 0.26) differ across aging periods; yet among LT steaks, consumers rated those aged 14 d greater ( < 0.05) in overall impression than LT steaks aged 28 and 42 d. Among LT steaks, those aged 14 d received greater ( < 0.05) flavor ratings than LT steaks subjected to longer aging periods, and LT steaks aged 14 d received the greatest ( < 0.05) overall impression, with consumers giving greater ( < 0.05) overall impression scores to LT steaks aged 42 d over those aged 28 d. Aging period had no effect ( ≥ 0.017) on consumer ratings for flavor, tenderness, juiciness, or overall impression of LL steaks. Among GM steaks, consumers rated steaks aged 14 and 28 d more ( < 0.05) flavorful than those aged 42 d, and consumer ratings for overall impression were greater ( < 0.05) for GM steaks aged 28 d than for GM steaks aged 42 d; however, consumers failed ( = 0.035) to note differences in tenderness scores of GM steaks in response to aging period. Furthermore, consumers indicated a greater ( < 0.05) likelihood to purchase LT steaks aged 14 d over LT steaks aged 28 d, LL steaks aged 42 d over LL steaks aged 14 d, and GM steaks aged 14 and 28 d over GM steaks aged 42 d. These results indicate that consumers struggled to identify steak flavor attributes and suggest that the benefit of aging for premium beef products does not offer a tremendous sensory advantage to the consumer.

Effect of electrical stimulation and hot boning on the eating quality of Gannan yak longissimus lumborum

The objective of this study was to evaluate the effects of electrical stimulation (ES) versus non-electrical stimulation (NES) and type of boning (hot versus cold) on the eating quality of Gannan yak longissimus lumborum. Eighteen Gannan yak bulls were randomly divided into two groups: ES and NES. Hot boning (HB) and cold boning (CB) were applied to the left and right side of the carcasses, respectively. All of the four treatments missed the "ideal" pH/temperature window. HB reduced the rate of pH decline, decreased meat tenderness and water holding capacity. ES increased the rate of pH decline and improved yak meat tenderness (P<0.05); however, ES explained only 1% of the variation in WBSF. HB and ES had no significant effects on cooking loss, L* or b* values of yak meat. Postmortem aging increased yak meat tenderness and improved meat color parameters. HB had negative effects on yak meat quality, while ES could not reverse these deleterious effects.

Effects of dry-aging on meat quality attributes and metabolite profiles of beef loins

The objectives of this study were to evaluate different dry-aging regimes and their impacts on quality attributes and metabolite profiles of beef loins. Thirty loins (M. longissimus lumborum) from 15 beef carcasses at 2 days post-mortem were obtained. Each loin was cut in half yielding 60 sections, which were randomly assigned to six treatments including 4 dry-aging (2 temperatures (1 or 3°C) × 2 air-velocities (0.2 or 0.5 m/s)) and 2 wet-aging regimes for 3 weeks; n=10/treatment. The sensory panel found that dry-aged loins had better flavour and overall liking (P<0.05), but there were no differences in tenderness and juiciness. No differences in drip/cook-loss and colour were observed. Metabolite analysis showed that 7 metabolites, including several flavour precursors, were more abundant in the dry-aged beef compared to the wet-aged beef, which may contribute to the enhanced flavours of the dry-aged beef. Overall, dry-aging loins at 3°C with 0.2m/s resulted in the greatest improvement in beef palatability.

Differences in calpain system, desmin degradation and water holding capacity between commercial Meishan and Duroc × Landrace × Yorkshire crossbred pork

The objective of this study was to examine the differences in calpain system, desmin degradation, pH values and water holding capacity (WHC) between muscles of commercial Meishan and Duroc × Landrace × Yorkshire crossbred pigs. Meishan pork presented better WHC evidenced by lower purge loss at days 1 and 3 and less centrifugation loss at day 1 post mortem (P < 0.05). pH values at 45 min post mortem in Meishan pork were significantly higher compared to crossbred pork (P < 0.05). Calpain-1 messenger RNA (mRNA) expression was lower in Meishan pork compared to that from crossbred pork (P < 0.05). Additionally, calpain-1 activity, the ratio of calpain-1 to calpastatin activity and desmin degradation were lower in Meishan pork compared to those from crossbred pork samples (P < 0.05). The results indicate that the calpain system including mRNA expression and activity were different between commercial Meishan and crossbred pork resulting in difference in the degree of desmin degradation during post mortem aging. pH values at 45 min and 24 h post mortem rather than calpain activity and desmin degradation could explain the higher water holding capacity in commercial Meishan pork.

Single-Nucleotide Polymorphisms in Pig EPHX1 Gene are Associated with Pork Quality Traits

Epoxide hydrolase 1 (EPHX1) plays an important role in both the activation and detoxification of exogenous chemicals. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the highest level of EPHX1 expression occurred in Berkshire liver, which is an organ that plays a key role in detoxification. We examined EPHX1 SNPs to analyze effect on increased expression of EPHX1 gene in Berkshire liver by total of 192 pigs of a pure Berkshire line (males = 97; females = 95). As a result, two nonsynonymous SNPs (nsSNPs) of EPHX1 were found from c.685T>G and c.776C > T, and located in 5th and 6th exons, respectively, which constitute the A/b hydrolase 1 domain of epoxide hydrolase. The nsSNP c.685T > G was significant differences in meat color, protein content, collagen content, and pH24 hr. Especially, T and G alleles of the nsSNP c.685T > G were significantly associated with CIE a*/CIE b* and protein content/pH24 hr, respectively. The nsSNP c.776C > T was significant differences in drip loss and protein content. Among meat quality traits to associate with SNPs, the protein content was only significantly associated with sex. Therefore, it is suggested that nsSNP c.685T > G in EPHX1 gene is a potential to apply as appropriate DNA markers for improvement of porcine economic traits.

Effects of ripening duration and rosemary powder addition on salchichon modified sausage quality

The ripening durations and ingredients for the Salchichon sausages were modified to increase pork rear leg consumption by Korean consumers. The salchichon, a ripened pork sausage, was produced to evaluate the efficacy of two different ripening durations with and without rosemary powder on salchichon sausage quality, and the treatments were: i) 45 days of ripening without rosemary, ii) 60 days of ripening without rosemary, iii) 45 days of ripening with 0.05% rosemary, and iv) 60 days of ripening with 0.05% rosemary. Significant differences were observed in both moisture and fat content for ripening durations, with the highest moisture and least fat content observed in salchichon modified sausage (SMS) ripened for 45 days. Ripening duration and rosemary addition appeared to influence water activity (a_w) of salchichon sausages. The a_w of SMS ripened for 45 days was 0.80, whereas the other had a_w values <0.80. Lactic acid bacteria were predominant, as Korean traditional fermented red pepper paste was added to sausages; however, the Bacillus cereus population was significantly affected by rosemary powder addition. Chewiness and gumminess decreased significantly due to the addition of rosemary powder compared to SMS without rosemary powder, and both 45 days of ripening and rosemary powder addition influenced the hardness of SMS. In conclusion, ripening duration of SMS for 45 days in the presence of rosemary powder provided superior SMS quality with an economical ripening duration compared to that of ripening with rosemary powder or ripening for 60 days.

Molecular characterization of porcine PGM1 gene associated with meat quality traits

Hwang, J. H., Kwon, S. G., Park, D. H., Kim, T. W., Kang, D. G., Ha, J., Kim, S. W. and Kim, C. W. 2015. Molecular characterization of porcine PGM1 gene associated with meat quality traits. Can. J. Anim. Sci. 95: 31–36. The PGM1 gene from four porcine breeds (Berkshire, Duroc, Landrace, and Yorkshire) is highly expressed in liver tissue at the transcriptional level. Single nucleotide polymorphisms (SNPs) of PGM1 were examined to analyze association with increased expression of PGM1 gene in the Berkshire liver. A Leu525 synonymous SNP of Chr6:137174682A>G (c.1575A>G) was identified and showed significant (P<0.05) differences to backfat thickness, drip loss, protein content, fat content, Warner–Bratzler shear force, and post-mortem pH24h. Therefore, it is concluded that PGM1 synonymous SNP is an important factor regulating meat quality.

Changes in Ultrastructure and Sensory Characteristics on Electro-magnetic and Air Blast Freezing of Beef during Frozen Storage

The ultrastructure in the beef muscle of the electro-magnetic resonance and air blast freezing during the frozen storage, and the changes in the quality characteristics after thawing were evaluated. The size of ice crystal was small and evenly formed in the initial freezing period, and it showed that the size was increased as the storage period was elapsed (p<0.05). The beef stored by the electro-magnetic resonance freezing showed the size of ice crystal with a lower rate of increase than the air blast freezing during the frozen storage. The thawing loss of beef stored by the electro-magnetic resonance freezing was significantly lower than the air blast freezing during frozen storage (p<0.05), and it showed that the thawing loss of the round was higher than the loin. Water holding capacity decreased as the storage period became longer while the electro-magnetic resonance freezing was higher than the air blast on 8 month (p<0.05). As a result of sensory evaluation, the beef stored by the electro-magnetic resonance freezing did not show the difference until 4 months, and it showed higher acceptability in comparison with the beef stored by the air blast freezing. Thus, it is considered that the freezing method has an effect on the change in the ultrastructure and quality characteristics of the beef.

Physico-chemical Meat Qualities of Loin and Top Round Beef from Holstein Calves with Different Slaughtering Ages

The objective of this study was to investigate the physico-chemical and sensory properties of loin (m. longissimus dorsi) and top round (m. semimembranosus) beef from 3-, 6-, 9-, and 12 mon-old Holstein calves. For both loin and top round muscles, the moisture contents were decreased, whereas the protein and fat contents were increased, as the slaughtering age increased. In terms of meat color, for both muscle types, CIE L* values were decreased, whereas CIE a* values and myoglobin content increased as the slaughtering age increased. pH values were significantly higher in the 3 mon-old group than in the other groups. The Warner-Bratzler shear force (WBSF) values were lowest for loin muscles from the 12 mon-old group; however, there was no significant difference for top round muscle among the 4 age groups. Cooking loss for both loin and top round muscles were significantly higher for the 3 mon-old group than for the other groups. The water holding capacity (WHC) of both muscles were highest for the 12 mon-old groups (p<0.05). In fatty acid composition of the 12 mon-old groups, loin muscles had significantly higher levels of C14:0, C16:1n7, C18:1n9, and mono-unsaturated fatty acids (MUFA), and top round muscles had significantly higher levels of C16:1n7, C18:1n7, C18:1n9, MUFA, MUFA/SFA. Loin muscle from the 3- and 12 mon-old groups had significantly higher scores for tenderness and overall likeness. Top round muscle from the 9- and 12 mon-old groups had significantly higher scores for overall likeness than those from the other age groups.

Quality Evaluation of Pork with Various Freezing and Thawing Methods

In this study, the physicochemical and sensory quality characteristics due to the influence of various thawing methods on electro-magnetic and air blast frozen pork were examined. The packaged pork samples, which were frozen by air blast freezing at -45℃ or electro-magnetic freezing at -55℃, were thawed using 4 different methods: refrigeration (4±1℃), room temperature (RT, 25℃), cold water (15℃), and microwave (2450 MHz). Analyses were carried out to determine the drip and cooking loss, water holding capacity (WHC), moisture content and sensory evaluation. Frozen pork thawed in a microwave indicated relatively less thawing loss (0.63-1.24%) than the other thawing methods (0.68-1.38%). The cooking loss after electro-magnetic freezing indicated 37.4% by microwave thawing, compared with 32.9% by refrigeration, 36.5% by RT, and 37.2% by cold water in ham. The thawing of samples frozen by electro-magnetic freezing showed no significant differences between the methods used, while the moisture content was higher in belly thawed by microwave (62.0%) after electro-magnetic freezing than refrigeration (54.8%), RT (61.3%), and cold water (61.1%). The highest overall acceptability was shown for microwave thawing after electro-magnetic freezing but there were no significant differences compared to that of the other samples.

Effect of Repeated Freeze-Thaw Cycles on Beef Quality and Safety

The objectives of this study were to know the effect of repeated freeze-thaw cycles of beef on the sensory, physicochemical quality and microbiological assessment. The effects of three successive freeze-thaw cycles on beef forelimb were investigated comparing with unfrozen fresh beef for 75 d by keeping at -20±1℃. The freeze-thaw cycles were subjected to three thawing methods and carried out to know the best one. As the number of freeze-thaw cycles increased color and odor declined significantly before cook within the cycles and tenderness, overall acceptability also declined among the cycles after cook by thawing methods. The thawing loss increased and dripping loss decreased significantly (p<0.05). Water holding capacity (WHC) increased (p<0.05) until two cycles and then decreased. Cooking loss increased in cycle 1 and 3, but decreased in cycle 2. pH decreased significantly (p<0.05) among the cycles. Moreover, drip loss, cooking loss and WHC were affected (p<0.05) by thawing methods within the cycles. 2-Thiobarbituric acid (TBARS) value increased (p<0.05) gradually within the cycles and among the cycles by thawing methods. Total viable bacteria, total coliform and total yeast-mould count decreased significantly (p<0.05) within and among the cycles in comparison to the initial count in repeated freeze-thaw cycles. As a result, repeated freeze-thaw cycles affected the sensory, physicochemical and microbiological qua- lity of beef, causing the deterioration of beef quality, but improved the microbiological quality. Although repeated freeze-thaw cycles did not affect much on beef quality and safety but it may be concluded that repeated freeze and thaw should be minimized in terms of beef color for commercial value and WHC and tenderness/juiciness for eating quality.

Quality Assessment of Longissimus and Semitendinosus Muscles from Beef Cattle Subjected to Non-penetrative and Penetrative Percussive Stunning Methods

This study provides a comparative analysis of the effects of pre-slaughter penetrative and non-penetrative stunning and post-slaughter stunning on meat quality attributes in longissimus lumborum (LL) and semitendinosus (ST) muscles in heifers. Ten animals were assigned to each of four treatment groups: i) animals were subjected to conventional Halal slaughter (a clean incision through the structures at the front of the upper neck - the trachea, oesophagus, carotid arteries and jugular veins) and post-cut penetrating mechanical stun within 10 to 20 s of the neck cut (Unstunned; US); ii) high power non-penetrating mechanical stunning followed by the neck cut (HPNP); iii) low power non-penetrating mechanical stunning followed by the neck cut (LPNP); and iv) penetrative stunning using a captive bolt pistol followed by the neck cut (P). For each carcass, muscle samples were removed within 45 min of slaughter, portioned and analysed for pH, cooking loss, water holding capacity (WHC), tenderness (WBS), lipid oxidation (TBARS) and color, over a two week storage period. Stunning did not affect pH and cooking loss. Significant differences in water holding capacity, tenderness, lipid oxidation and color were present at different storage time points. HPNP stunning resulted in lower WHC and color values, particularly lightness (L*), higher TBARS values and peak force values compared with those stunned using LPNP, P and US. These adverse effects on quality were mostly encountered in the ST muscle. In conclusion, the meat quality achieved using P, LPNP and US treatments was comparable, and no treatment stood out as considerably better than another.

Trends in meat science and technology: the future looks bright, but the journey will be long

With an increasing world population, an increase in affluence and a substantial growth in the demand for high quality protein, the meat sector faces a fantastic but challenging century. New scientific knowledge, technology and creative minds are the main ingredients in order to reach out for this great opportunity. Efficiency all the way from breeding and farming to processing and dispatch is crucial for success. Technology has brought us far, and there is still a huge potential for increased efficiency by implementing best practices on a global scale. New challenges include: hyper flexible automation, more accurate and faster measurement systems and meeting special consumer demands already at the production line. Systems for optimal animal welfare will be even more important and sustainability is no longer a consumer trend but a license to operate. The scientific meat society must provide knowledge and technology so we together can reach out for a seemingly bright future.

A structural approach to understanding the interactions between colour, water-holding capacity and tenderness

The colour, water-holding capacity (WHC) and tenderness of meat are primary determinants of visual and sensory appeal. Although there are many factors which influence these quality traits, the end-results of their influence is often through key changes to the structure of muscle proteins and their spatial arrangement. Water acts as a plasticiser of muscle proteins and water is lost from the myofibrillar lattice structure as a result of protein denaturation and consequent reductions in the muscle fibre volume with increasing cooking temperature. Changes in the myofilament lattice arrangement also impact the light scattering properties and the perceived paleness of the meat. Causes of variation in the quality traits of raw meat do not generally correspond to variations in cooked meat and the differences observed between the raw muscle and cooked or further processed meat are discussed. The review will also identify the gaps in our knowledge and where further investigation would beneficial.

UBXN1 polymorphism and its expression in porcine M. longissimus dorsi are associated with water holding capacity

The UBX domain containing protein 1-like gene (UBXN1) promotes the protein degradation that affects meat quality, in particular traits related to water holding capacity. The aim of our study was to identify UBXN1 polymorphisms and to analyse their association with meat quality traits. Moreover, the relationship of UBXN1 polymorphisms and its transcript abundance as well as the link between UBXN1 expression and water holding capacity were addressed. Pigs of the breed German landrace (GL) and the commercial crossbreed of Pietrain × [German large white × GL] (PiF1) were used for this study. In GL, the novel SNP c.355 C > T showed significant association with conductivity and drip loss (P ≤ 0.05). Another SNP at nt 674 of the coding sequence [SNP c.674C>T (p.Thr225Ile)] was associated with drip loss (P ≤ 0.05) and pH1 (P ≤ 0.1). In PiF1, the SNP UBXN1 c.674C>T was associated with conductivity (P ≤ 0.01). Moreover, the haplotype combinations showed effects on conductivity within both commercial populations at P ≤ 0.1. In both populations, high expression of UBXN1 tended to decrease water holding capacity in the early post mortem period. The analysis of triangular relationship of UBXN1 polymorphism, transcript abundance, and water holding capacity evidences the existence of a causal polymorphism in cis-regulatory regions of UBXN1 that influences its expression.

Eating quality of beef from free-range and confined Podolian young bulls

The purpose of the present study was to assess the effect of grazing on meat quality of young Podolian bulls by using 6 free-ranging (FR) and 6 confined (CON) animals slaughtered at 18 mo of age (Exp. 1). A second experiment (Exp. 2) was performed the subsequent year where the age at slaughter was 15 mo of age (6 animals/group). Quantitative descriptive sensory analysis, water-holding capacity (WHC; thawing, centrifugation, and cooking losses), and shear force (only in Exp. 2) were evaluated on LM, aged 8 d. Both experiments showed that CON animals produced beef with greater overall beef flavor (P < 0.01 and P < 0.05 in Exp. 1 and 2, respectively) and odor intensities (P < 0.10 and P < 0.05 in Exp. and 1 and 2, respectively) and increased malondialdehyde contents (P < 0.01 and P < 0.05 in Exp. 1 and 2, respectively). In Exp. 2 beef from FR bulls showed higher sensory tenderness as compared with CON bulls (P < 0.05) and a lower shear force (P < 0.05). In Exp. 1, beef obtained from FR bulls showed lower centrifugation and greater thawing losses compared with samples from bulls from group CON (P < 0.05) whereas rearing system did not affect any WHC variables in Exp. 2. The results obtained from the 2 experiments were generally consistent. The different results occasionally observed (e.g., sensory tenderness and WHC) is attributed to the different ages at slaughter used in the 2 experiments (18 and 15 mo). In particular, at an earlier age at slaughter (15 mo) the effect of FR on meat quality was beneficial on sensory tenderness and mechanical properties. Therefore, given the additional costs of maintaining the bulls for another 3 mo when slaughtered at 18 mo of age, a reduced age at slaughter of FR bulls may be suggested to avoid the decrement of herbage mass availability inducing the consumption of high amounts of concentrate.

Influence of meat exudates on the quality characteristics of fresh and freeze-thawed pork

The influence of the accumulated exudates released from pork loin of itself on the quality characteristics of fresh and freeze-thawed pork during cold storage was investigated. Pork loins were divided into four groups (fresh pork with exudates, fresh pork without exudates, freeze-thawed pork with exudates and freeze-thawed pork without exudates) and stored at 1.0°C for 7 days. Exudate amount increased due to freeze-thawing and with storage, and most quality traits such as drip loss, cooking loss, tenderness, lightness, redness, and moisture content were affected by freeze-thawing (p<0.05). Freeze-thaw increased drip loss but decreased moisture content, cooking loss, tenderness, lightness and redness of meat (p<0.05). Microbial growth was solely affected by exudate removal and the removal of initial exudates decreased microbial growth (p<0.05). Exudates were positively correlated with total protein content and total plate count but negatively correlated with pH and cooking loss. Therefore, removing meat exudates and avoiding freeze can slow down the quality deterioration of pork during cold storage.

Monitoring post mortem changes in porcine muscle through 2-D DIGE proteome analysis of Longissimus muscle exudate

Background

Meat quality is a complex trait influenced by a range of factors with post mortem biochemical processes highly influential in defining ultimate quality. High resolution two-dimensional DIfference Gel Electrophoresis (2-D DIGE) and Western blot were applied to study the influence of post mortem meat ageing on the proteome of pork muscle. Exudate collected from the muscle following centrifugation was analysed at three timepoints representing a seven day meat ageing period.

Results

The intensity of 136 spots varied significantly (p < 0.05) across this post mortem period and 40 spots were identified using mass spectrometry. The main functional categories represented were metabolic proteins, stress-related proteins, transport and structural proteins. Metabolic and structural proteins were generally observed to increase in abundance post mortem and many likely represent the accumulation of the degradation products of proteolytic enzyme activity. In contrast, stress-related proteins broadly decreased in abundance across the ageing period. Stress response proteins have protective roles in maintaining cellular integrity and a decline in their abundance over time may correlate with a reduction in cellular integrity and the onset of meat ageing. Since cellular conditions alter with muscle ageing, changes in solubility may also contribute to observed abundance profiles.

Conclusions

Muscle exudate provided valuable information about the pathways and processes underlying the post mortem ageing period, highlighting the importance of post mortem modification of proteins and their interaction for the development of meat quality traits.

Proteomic analysis of duck fatty liver during post-mortem storage related to the variability of fat loss during cooking of "foie gras"

Fat loss during cooking of duck "foie gras" is the main problem for both manufacturers and consumers. Despite the efforts of the processing industry to control fat loss, the variability of fatty liver cooking yields remains high and uncontrolled. To understand the biochemical effects of postslaughter processing on fat loss during cooking, this study characterizes for the first time the protein expression of fatty liver during chilling using a proteomic approach. For this purpose the proteins were separated according to their solubility: the protein fraction soluble in a buffer of low ionic strength (S) and the protein fraction insoluble in the same buffer (IS). Two-dimensional electrophoresis was used to analyze the S fraction and mass spectrometry for the identification of spots of interest. This analysis revealed 36 (21 identified proteins) and 34 (26 identified proteins) spots of interests in the low-fat-loss and high-fat-loss groups, respectively. The expression of proteins was lower after chilling, which revealed a suppressive effect of chilling on biological processes. The shot-gun strategy was used to analyze the IS fraction, with the identification of all the proteins by mass spectrometry. This allowed identification of 554 and 562 proteins in the low-fat-loss and high-fat-loss groups, respectively. Among these proteins, only the proteins that were up-regulated in the high-fat-loss group were significant (p value = 3.17 × 10(-3)) and corresponded to protein from the cytoskeleton and its associated proteins. Taken together, these results suggest that the variability of technological yield observed in processing plants could be explained by different aging states of fatty livers during chilling, most likely associated with different proteolytic patterns.

The effects of aging on moisture-enhanced pork loins

The effects of preinjection aging time on pork loins injected with a salt/phosphate/lactate solution were investigated. Ninety-six fresh pork loins, in two replicates, were divided into two treatments. Loins in the first treatment were injected to 13% of loin weight at 1 day post-slaughter with a brine containing 2.17% salt/3.04% phosphate/20.8% lactate. The second group was injected with the same brine 4 days after slaughter. Color and Warner-Bratzler shear (WBS) force were measured immediately, 7 and 14 days after injection. Purge was measured 8 and 15 days postmortem. Western blots to measure troponin-T degradation were performed on samples from the two loins that resulted in the lowest shear force, and from the two loins that resulted in the highest shear force, as measured by Warner-Bratzler shear. The two loins with the most purge loss and the two loins with the least purge loss were also analyzed by Western blots for desmin degradation. The L(∗) and b(∗) color values were higher (P<0.05) and purge was greater (P<0.05) for loins injected 1 day postmortem than for loins injected 4 days postmortem. Western blots demonstrated that injection did not affect protein degradation. Therefore, differences between individual animals that affect protein degradation remain important regardless of injection treatment.

Cleavage of desmin by cysteine proteases: Calpains and cathepsin B

The intermediate filament protein, desmin, was purified from pork longissimus dorsi and incubated with either μ-calpain, m-calpain or cathepsin B. Proteolysis of desmin was followed using SDS-PAGE and Western blotting. After incubation of desmin with the proteases, cleavage sites on the desmin molecule were identified by N-terminal sequencing of the different proteolytic fragments. Desmin incubated with either m-calpain or μ-calpain was primarily cleaved in the head and tail region leaving the rod domain relatively intact even after prolonged incubation. Incubation with cathepsin B produces a sequential C-terminal degradation pattern characteristic of this dipeptylpeptidase. The substrate primary structure was not found to be essential for regulation of the proteolytic activity of the cysteine peptidases studied. However, the degradation patterns obtained imply that calpains are involved in degradation of desmin early post-mortem, targeting the non-helical region of the desmin molecule and resulting in depolymerisation and initial disorganisation of the intermediate filament structures of the muscle cell.

The role of integrin degradation in post-mortem drip loss in pork

Cell membranes are attached to the cell body by two major types of adhesion complexes, integrin-containing focal adhesions and the dystrophin/dystroglycan complex of proteins. In this study, we used samples with known and varying rates of drip channel formation to determine whether the time frame of formation of the channels correlated with the rate of cell/membrane adhesion protein degradation. Our results indicate that the degradation of the β1-chain of integrin, the portion of the protein involved in adhesion of the cell membrane to the cytoskeleton, temporally correlates to the opening of drip channels in pork, while dystrophin degradation does not. Additionally, this degradation may be due to activation of calpains at the site of adhesion plaques. Previous work has indicated that calpains can degrade the β-chain of integrins in vitro. We find that m-calpain is co-localized with β1-integrin at the cytoplasmic surface of the cell membrane in plaque-like structures and is active in these regions post-mortem. Inhibition of calpains not only results in inhibition of integrin degradation, but blocks the opening of drip channels. Therefore, the opening of drip channels in pork may well be due to the degradation of integrin proteins on the cell surface by calpains.

Effect of very fast chilling and aging time on ultra-structure and meat quality characteristics of Chinese Yellow cattle M. Longissimus lumborum

Objectives of the current study were to evaluate meat ultra-structure and tenderness variation at different chilling regimes and aging times. Hot boned longissimus lumborum of 18 Chinese crossbred cattle were divided into 4 portions per side. One portion underwent very fast chilling (VFC, at -21 °C to achieve core temperature of 0 °C, then transferred to another incubator at 2 °C), whereas other treatments were held at 14, 7 and 0 °C for 10 h postmortem, respectively. At 10 h postmortem, all muscles were vacuum aged at 2 °C for 21 d. Cold shortened muscles had greatest absolute amount of tenderization during aging. VFC caused lowest sarcomere length, with super-contractions, ruptured Z-lines and myofibril cleavage, but improved myofibril fragmentation index (MFI), with no significant negative effect on toughness. Overall, aging improved the meat quality of cold shortened beef. Moreover, it should be prudent in some applications to apply VFC to excised muscles from a food safety perspective, and to improve tenderness compared to cold-shortened muscles.