Role of freezing-induced myofibrillar protein denaturation in the generation of thaw loss: A review.

Formation of thaw loss cannot generally be avoided when meat is frozen and then thawed. Explanations have mainly focused on the damage to muscle fibers resulting from ice crystallization and the freezing-induced denaturation of myofibrillar proteins, the latter of which has, however, not received much research focus. This review discusses the relationship between myofibrillar protein denaturation and water-holding capacity of meat in freezing-thawing with the aim to improve the understanding the relative importance of protein denaturation in the formation of thaw loss. The contribution of decreased pH and high ionic strength in the unfrozen water in freezing is emphasized and we hypothesize that these two factors are causing protein denaturation and conformational changes within muscle fibers, and consequently loss of water-holding capacity. Slow freezing produces more thaw loss than fast freezing, and this is discussed here in relation to the impacts on myofibrillar protein denaturation induced by the freezing rate.

Effects of probiotic (Bacillus subtilis) supplementation on meat quality characteristics of breast muscle from broilers exposed to chronic heat stress.

The aim of this study was to determine the impact of probiotic feeding and chronic heat stress on meat quality, total lipid and phospholipid contents, lipid oxidation, antioxidant capacity, and heat shock protein abundance of broiler breast muscle. A total of 240 male broilers (5 birds per pen) were subjected to 4 treatments consisting of a 2 × 2 factorial design. Broilers were kept at 21-32-21°C for 10 h daily (heat stress, HS) or 21°C (thermoneutral condition) and fed a regular diet or the diet mixed with probiotic (250 ppm of Sporulin containing 3 strains of Bacillus subtilis). A total of 48 broilers (12 birds/treatment) were harvested at 46 d. Neither HS nor probiotic had substantial impacts on water-holding capacity, shear force, and color characteristics. HS induced lipid oxidation as increased 2-thiobarbituric acid reactive substances (TBARS), in which probiotic feeding decreased TBARS value (P = 0.002) and phospholipid contents (P = 0.0033) in breast muscle of HS broilers. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was increased with HS (P < 0.0001), but no significant impact of probiotic supplementation was found. Neither probiotic nor HS affected catalase activity, but superoxide dismutase and glutathione peroxidase activities were lower in HS broilers compared to thermoneutral controls (P < 0.0001) and in probiotics-fed broilers (P < 0.0001) compared to their counterparts. In addition, a significant interaction between probiotic and HS was found at glutathione peroxidase activities, in which breast muscle of broilers fed probiotic at thermoneutral condition showed the highest activity (P < 0.05). Regarding heat shock protein (HSP) determination, HS slightly increased the levels of both HSP70 (P = 0.08) and HSP27 (P = 0.05), but no significant impacts of probiotic supplementation were found. Our results indicate that probiotic feeding could improve breast muscle weight without adverse impacts on meat quality attributes, as well as alleviate oxidative deterioration of breast muscle of broilers undergoing heat stress.

Effects of probiotics feeding on meat quality of chicken breast during postmortem storage.

This study evaluated the effects of dietary probiotic supplement and postmortem storage on meat quality of chicken breast during retail display. A total of 35 birds were randomly obtained from 3 feeding groups (control without probiotic supplement, 250 ppm Sporulin, and 500 ppm PoultryStar). The probiotic supplement had no influence on feed conversion ratio and body weight gain, as well as body weight at 29 and 44 d (P > 0.05). After slaughter, each side of the breast muscles (M. Pectoralis major) was assigned to either one d or 5 d of postmortem storage. Probiotic supplement had no influence on the rate of pH decline of chicken breast muscles during the initial 6 h postmortem (P > 0.05). No interactions between probiotic supplement and postmortem storage on meat quality were found (P > 0.05). Postmortem storage decreased drip loss from 25.30 to 18.05% (P < 0.05). Probiotics-fed chicken groups, particularly PoultryStar treatment, had a higher myofibrillar fragmentation index than the control group (P < 0.05). However, shear force values were not affected by the probiotic treatments. Decreases in color and lipid stabilities of breast muscles were found during display (P < 0.05), but were not affected by the probiotic supplement (P > 0.05). Our result suggests that probiotic supplement had no adverse impacts on proteolysis and oxidative changes during 5 d postmortem display storage.

Effect of forage and retail packaging types on meat quality of long-term chilled lamb loins.

The objectives of this study were to determine the effects of different forage regimes and modified atmosphere packaging (MAP) systems [high oxygen (HiOx-MAP): 80% O2 and 20% CO2; and CO2-MAP: 20% CO2 and 80% N2] on color and lipid oxidation stability and sensory attributes of long-term chilled lamb loins during retail display. Lambs (n = 124) were randomly assigned to several pasture-feeding regimes for 12 wk before slaughter. Some had ryegrass (n = 18), lucerne (n = 18), chicory (n = 19), plantain (n = 16), or red clover (Clover 12; n = 17) for all 12 wk. Some were assigned a regime of red clover for 11 wk and pasture for 1 wk (Clover 11; n = 18), with others on red clover for 9 wk and pasture for 3 wk (Clover 9; n = 18). After the lambs were slaughtered, the paired loins (M. longissimus dorsi) were excised at 24 h postmortem, vacuum-packed and stored at -1.5 °C for 9 wk. Cuts were then made from each loin and randomly allocated to either HiOx-MAP or CO2-MAP, and displayed for 7 d at 4 °C under light. Chemical attributes including lipid oxidation, surface color-reversing ability, oxygen consumption, and meat quality attributes (color stability and sensory characteristics) were determined. Among the different forage types, the loins from lambs finished on ryegrass appeared to have greater color stability and less lipid oxidation than the loins from lambs finished on other forage types (P < 0.05). On the other hand, the loins from lambs finished on lucerne had the least color and lipid oxidation stabilities and least color-reversing ability (P < 0.05). The loins from lambs finished on chicory had higher aroma and flavor scores than other pasture types in general (P < 0.05). HiOx-MAP negatively influenced meat quality attributes of lamb loins during display, as substantial increases in surface discoloration and lipid oxidation were observed, along with significant decreases in aroma and flavor during retail display compared with the loins in CO2-MAP. These results suggest that different forage types and packaging conditions could result in substantial impacts on meat quality attributes of long-term chilled lamb loins by affecting oxidation stability. Furthermore, the present study suggests that CO2-MAP could provide beneficial effects on the eating quality of long-term chilled lamb loins by suppressing oxidation-related defects during display without compromising the ability of blooming for meat display.

Effect of low voltage electrical stimulation on protein and quality changes in bovine muscles during postmortem aging.

This experiment was conducted to determine the influence of low voltage electrical stimulation (ES) on the tenderness development of beef round muscles. Eight steers were slaughtered, and ES applied to one side of each carcass within 90 min of exsanguination. Steaks from M. longissimus dorsi, semimembranosus, adductor, and gracilis were vacuum packaged and aged at 4 °C for 9 d. Star probe, sensory evaluation, Western blot assays of troponin-T and µ-calpain autolysis and 2D-DIGE were conducted. ES resulted in accelerated (P<0.05) pH decline of the longissimus in the first 24h postmortem. ES did not influence (P>0.05) proteolysis and tenderness, but did alter the predominance of metabolic proteins in the soluble fraction of muscle. Aging for 9 d improved tenderness (P<0.05). The data confirmed that low voltage ES at 90 min of exsanguination had no effect on proteolysis and tenderness development in the longissimus dorsi, semimembranosus, adductor or gracilis in beef.