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.

Fresh and cooked color of dark-cutting beef can be altered by post-rigor enhancement with lactic acid

Fresh and cooked color of dark-cutting (DC) beef strip loins (mean pH=6.56) enhanced with 0.25, 0.50, 0.75 or 1.00% lactic acid (LA) were compared to non-enhanced DC and normal pH (NpH; mean pH=5.43) strip loins. Even though NpH steaks received the most (P<0.05) desirable fresh color scores, color scores for steaks from DC sections enhanced with 0.25% LA approached those of NpH steaks after the first day of retail display. Discoloration scores were also similar (P>0.05) among NpH and 0.25% LA-enhanced DC steaks throughout the 5 d of display. Fresh steaks from NpH strip loins were redder, as evidenced by greater (P<0.05) a(∗) values and lower (P<0.05) hue angles, than DC steaks and DC steaks enhanced with LA, regardless of concentration. However, cooked color scores and proportions of denatured myoglobin were similar (P>0.05) between untreated NpH steaks and DC steaks enhanced with 0.25% LA. Results from this study indicate that enhancing DC beef with LA may lead to the brightening of the fresh color and prevention of the persistent red cooked color, approaching that of NpH beef.

Interactive effect of ractopamine and dietary fat source on quality characteristics of fresh pork bellies1

Crossbred pigs (n = 216) were used to test the interaction, if any, of ractopamine (RAC) and dietary fat source on the characteristics of fresh pork bellies. Pigs were blocked by BW (77.6 +/- 6.5 kg) and allotted randomly to pens (6 pigs/pen). After receiving a common diet devoid of RAC for 2 wk, pens within blocks were assigned randomly to 1 of 4 treatments arranged in a 2 x 2 factorial design, with 5% fat (beef tallow vs. soybean oil) and RAC (0 vs. 10 mg/kg). At the conclusion of the 35-d feeding period, pigs were slaughtered at a commercial pork packing plant (average BW of 108.8 +/- 0.6 kg), and fresh bellies were captured during carcass fabrication. Neither RAC (P = 0.362) nor fat source (P = 0.247) affected belly thickness. Subjective (bar-suspension) or objective (compression test) measures of belly firmness were not (P > or = 0.148) affected by the inclusion of RAC in the diet; however, bellies from pigs fed soybean oil (SBO) were softer than those from pigs fed beef tallow (BT), as indicated by perpendicular (P < or = 0.005) and parallel (P < 0.001) suspensions. Moreover, bellies from BT-fed pigs required more (P = 0.096) force to compress 50% of their thickness than bellies from SBO-fed pigs (52.29 vs. 43.51 kg). Color (L*, a*, and b* values) of the belly lean and fat was not (P > or = 0.131) affected by RAC, and lean color was similar (P > or = 0.262) between fat sources; however, belly fat from BT-fed pigs was lighter (P = 0.030) and redder (P = 0.013) in color than belly fat from SBO-fed pigs. Bellies of SBO-fed pigs had greater (P < 0.001) proportions of PUFA and lower (P < 0.001) proportions of SFA and MUFA than belly fat from pigs fed BT. Regardless of the RAC inclusion level, PUFA:SFA and iodine values were lower in belly fat from pigs fed BT than SBO; however, within SBO-fed pigs, PUFA:SFA and iodine values were further increased by feeding RAC (RAC x fat source, P < 0.001). As expected, dietary fat source altered the fatty acid composition of fresh pork bellies, which subsequently impacted fresh belly firmness. Interestingly, including RAC in swine finishing diets exacerbated the effect of feeding SBO on pork fat polyunsaturation.

Effect of supplemental iron on finishing swine performance, carcass characteristics, and pork quality during retail display1

Crossbred pigs (n = 185) were used to test the effects of dietary Fe supplementation on performance and carcass characteristics of growing-finishing swine. Pigs were blocked by BW, allotted to pens (5 to 6 pigs/pen), and pens (5 pens/block) were allotted randomly to either negative control (NC) corn-soybean meal grower and finisher diets devoid of Fe in the mineral premix, positive control (PC) corn-soybean meal grower and finisher diets with Fe included in the mineral premix, or the PC diets supplemented with 50, 100, or 150 ppm Fe from Availa-Fe (an Fe-AA complex). When the lightest block averaged 118.2 kg, the pigs were slaughtered, and bone-in pork loins were collected during fabrication for pork quality data. During the grower-I phase, there was a tendency for supplemental Fe to reduce ADG linearly (P = 0.10), whereas in the grower-II phase, supplemental Fe tended to increase ADG linearly (P = 0.10). Even though pigs fed NC had greater G:F during the finisher-I phase (P < 0.05) and across the entire trial (P = 0.07), live performance did not (P > or = 0.13) differ among dietary treatments. There were linear increases in 10th-rib fat depth (P = 0.08) and calculated fat-free lean yield (P = 0.06); otherwise, dietary Fe did not (P > 0.19) affect pork carcass muscling or fatness. Moreover, LM concentrations of total, heme, and nonheme Fe were similar (P > 0.23) among treatments. A randomly selected subset of loins from each treatment was further fabricated into 2.5-cm-thick LM chops, placed on styrofoam trays, overwrapped with polyvinyl chloride film, and placed in coffin-chest display cases (2.6 degrees C) under continuous fluorescent lighting (1,600 lx) for 7 d. During display, chops from NC-fed pigs and pigs fed the diets supplemented with 100 ppm Fe tended to have a more vivid (higher chroma value; P = 0.07), redder (higher a* value; P = 0.09) color than LM chops of pigs fed 50 ppm of supplemental Fe. Moreover, greater (P < 0.01) redness:yellowness ratios in chops from pigs supplemented with 100 ppm Fe indicated a more red color than chops from PC-fed pigs or pigs fed diets supplemented with 50 ppm Fe. In conclusion, however, increasing dietary Fe had no appreciable effects on performance, carcass, or LM characteristics, suggesting that current dietary Fe recommendations are sufficient for optimal growth performance, pork carcass composition, and pork quality.

Effects of supplemental manganese on performance of growing-finishing pigs and pork quality during retail display

Crossbred barrows and gilts (n = 168) were used to test the effects of supplemental Mn during the growing-finishing period on performance, pork carcass characteristics, and pork quality during 7 d of retail display. Pigs were blocked by BW and allotted within blocks to pens (5 pigs/pen in blocks 1, 2, 5, and 6, and 4 pigs/pen in blocks 3 and 4). A total of 36 pens was randomly assigned to 1 of 6 dietary treatments, where the basal diets were formulated with (PC) or without (NC) Mn in the mineral premix, and supplemented with 0 or 350 ppm (as-fed basis) of Mn from MnSO4 or a Mn-AA complex (AvMn). Pigs were slaughtered at a commercial pork packing plant when the lightest block of pigs averaged 113.6 kg. During fabrication, boneless pork loins were collected and transported to Oklahoma State University, where 2.5-cm-thick LM chops were packaged in a modified atmosphere (80% O2 and 20% CO2) and subsequently placed in display cases (2 to 4 degrees C) under continuous fluorescent lighting (1,600 lx) for 7 d. Pig performance was not (P > or = 0.44) affected by supplemental Mn; however, during the grower-II phase, pigs fed the basal diets including Mn consumed less (P < 0.02) feed and tended to be more efficient (P < 0.09) than pigs fed the basal diets devoid of Mn. Throughout the entire feeding trial, neither dietary nor supplemental Mn altered (P > or = 0.22) ADG, ADFI, or G:F. Chops from pigs fed the diets supplemented with MnSO4 received greater (P < or = 0.05) lean color scores and had a redder (greater a* and hue angle values), more vivid color than chops from pigs fed the diets supplemented with AvMn. Additionally, LM chops from pigs fed the PC diets supplemented with MnSO4 were darker (lower L* values; P < 0.05) than chops from pigs fed the NC diets or PC diets supplemented with 0 or 350 ppm of AvMn. Even though discoloration scores were similar during the first 4 d of display, chops from pigs fed the PC diets supplemented with MnSO4 were less (P < 0.05) discolored on d 6 and 7 of retail display than chops from pigs fed the PC or NC diets and diets supplemented with AvMn (dietary treatment x display time, P = 0.04). Results of this study indicate that feeding an additional 350 ppm of Mn from MnSO4 above the maintenance requirements of growing-finishing pigs does not beneficially affect live pig performance but may improve pork color and delay discoloration of pork during retail display.

Lateral and longitudinal characterization of color stability, instrumental tenderness, and sensory characteristics in the beef semimembranosus

The objectives of this study were to evaluate longitudinal and lateral variations in color stability and sensory characteristics of the semimembranosus from each muscle location (dorsal=D, medial=M, ventral=V), and within each steak subsequently divided into four regions (caudal-distal=CaD, cranial-distal=CrD, caudal-proximal=CaP, cranial-proximal=CrP). Instrumental color assessment indicated that L(∗) (lightness) values tended to be lower for the CaD and CrD regions of all muscle locations, with higher L(∗) values recorded for the CrP regions of muscle sections. Instrumental tenderness measurements for Meullenet-Owens razor and Warner-Bratzler shear force values were generally lower for the CaD region of the D section, whereas regions within the V section were tougher and required greater shear force. Sensory panelists perceived lower amounts of connective tissue in the CaD of the D section, which tended to be more tender, whereas higher levels of connective tissue and greater toughness occurred in the CaP and CrP regions of the M and V sections. These results provide a detailed muscle profile of the quality variation within the semimembranosus, and may be used to further enhance the fabrication and marketability of this beef subprimal cut.

Dithiothreitol treatment induces heterotypic aggregation of newly synthesized secretory proteins in HepG2 cells

To analyze the importance of the endoplasmic reticulum oxidizing state for the folding and aggregation of newly made polypeptides, we have incubated intact HepG2 hepatoma cells in the presence of dithiothreitol. When dithiothreitol-treated cells were extracted under nondenaturing conditions immunoprecipitates of newly synthesized albumin showed a complex polypeptide profile. Using direct and sequential immunoprecipitation protocols we identified eight other polypeptide chains, transferrin, plasminogen, ceruloplasmin, alpha 2-macroglobulin, the three fibrinogen chains, and haptoglobin, that were among the proteins co-immunoprecipitated with albumin. The heterotypic aggregates are larger than several hundred kilodaltons and are stabilized by noncovalent interactions. Of the 10 polypeptide chains we examined, only one, alpha 1-antitrypsin, failed to aggregate. This protein is distinguished from the others by the absence of disulfide bonds. We propose a model in which the function of the oxidizing conditions of the endoplasmic reticulum is to promote the rapid formation of disulfide bonds that stabilize adhesive domains in a buried state, thus preventing "global" heterotypic aggregation of newly synthesized chains.

Early disulfide bond formation prevents heterotypic aggregation of membrane proteins in a cell-free translation system

We previously demonstrated that a heterotypic complex of the two rat asialoglycoprotein receptor subunits was assembled during cell-free translation (Sawyer, J. T., and D. Doyle. 1990. Proc. Natl. Acad. Sci. USA. 87:4854-4858). We have characterized this system further by analyzing polypeptide interactions under both reducing and oxidizing translation conditions. This report shows that the complex represents a heterogeneous interaction between reduced membrane proteins rather than a specific oligomeric structure. In the reduced state membrane proteins interact in this system to form aggregates of diverse size and composition. The aggregated nascent polypeptides interact with the immunoglobulin heavy chain binding protein but this protein is not an integral component of the aggregate. Aggregation occurs via the exoplasmic domain, rather than the transmembrane domain, and the folding of this domain by the formation of intramolecular disulfides, prevents the interaction from occurring. Additionally, the folded molecules containing intramolecular disulfides lack high affinity binding activity and thus appear to resemble the earliest folding intermediates seen in vivo (Olson, J. T., and M. D. Lane. 198. FASEB (Fed. Am. Soc. Exp. Biol.) J. 3:1618-1624). These results lead us to suggest that the formation of intramolecular disulfides during early biogenesis serves to prevent nonspecific associations between nascent polypeptides.

Assembly of a heterooligomeric asialoglycoprotein receptor complex during cell-free translation

We have translated RNAs for the two rat asialoglycoprotein receptor polypeptides together in a cell-free system containing dog pancreatic microsomes and immunoprecipitated the products with antibodies that distinguish the two proteins. In this system the proteins oligomerize, as judged by their coprecipitation with either of the subunit-specific antisera. Oligomerization does not occur between subunits synthesized without microsomes or between subunits synthesized on separate microsomes mixed during detergent solubilization. Thus, oligomerization occurs within the microsomal membrane. We calculate that oligomerization proceeds with an efficiency of approximately 85%. The receptor complex appears to represent a specific oligomer because it excludes a third membrane glycoprotein synthesized in the same reaction. Oligomerization of the asialoglycoprotein receptor in vitro should provide a useful system to study the assembly of a membrane-protein complex.

Identification of a complex of the three forms of the rat liver asialoglycoprotein receptor

We have generated antibodies against synthetic peptides which represent the carboxyl terminus of either the major, or the two minor, forms of the rat hepatic lectin which recognizes galactose-terminated glycoproteins (asialoglycoproteins). The antibodies were shown to be specific for the form of the lectin containing the immunizing peptide sequence by the following: reaction with purified lectin after sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoprecipitation of sodium dodecyl sulfate-denatured lectin, immunoprecipitation of lectin synthesized in vitro. These antibodies, however, precipitated all three rat hepatic lectin forms from nonionic detergent extracts of hepatocytes labeled with 125I via the lactoperoxidase catalyzed technique. A similar result was obtained if antibody was bound to intact cells prior to solubilization with detergent and collection of the immune complexes. We conclude that at least the plasma membrane-associated fraction of the rat hepatic lectin forms exists as a heterotypic complex.

Differential redistribution of lectin receptor classes on clonal rat myotubes and myoblasts

To evaluate the relative mobilities of cell surface glycoconjugates during myogenesis we have studied the redistribution of fluorescein-conjugated plant lectins on L6 rat myogenic cells. Previous experiments had demonstrated that the receptors for the lectins soybean agglutinin (SBA), wheat germ agglutinin, concanavalin A and Lens culinaris agglutinin all were relatively uniformly distributed on both myoblasts and myotubes, and that SBA receptors were capable of rapid redistribution on myotubes but not myoblasts at 4 degrees C (Sawyer & Akeson, 1983). Here we show that when SBA-labelled myoblasts are incubated at 37 degrees C, or for extended times at 4 degrees C, the lectin aggregates as on myotubes. So it appears that SBA-binding components show a quantitative rather than qualitative change in their mobility during L6 differentiation. In addition, the redistribution of the three other lectins on myoblasts and myotubes was either less prominent (i.e. showing fewer apparent surface clusters) or occurred less rapidly than with SBA. None of these three lectins showed striking differences in mobility between myoblasts and myotubes. Thus, it appears that SBA binds to a subset of surface glycoconjugates that is relatively highly mobile, and that this mobility is specifically enhanced with differentiation.

Clonal myoblasts and myotubes show differences in lectin-binding patterns

To determine changes in distribution or mobility of cell-surface glycoconjugates during myogenesis the binding of fluorescein-conjugated plant lectins to myoblasts and myotubes of the L6 rat skeletal muscle cell line has been studied. Binding has been carried out at 4 degrees C on either live or glutaraldehyde-fixed cells. Fluorescein conjugates of soybean agglutinin (Fl-SBA), wheat germ agglutinin (Fl-WGA), concanavalin A (Fl-conA) and Lens culinaris agglutinin (Fl-LCA) produced predominantly uniform fluorescence on both live and fixed myoblasts. On fixed myotubes, Fl-LCA, Fl-conA and Fl-SBA again produced predominantly uniform fluorescence, whereas Fl-WGA showed a pattern of diffuse, irregular spots in addition to uniform fluorescence. Fl-conA, Fl-LCA and Fl-WGA binding to live myotubes resulted in patterns quite similar to those on fixed myotubes; the only differences being the presence of weak patterns of diffuse spots with Fl-LCA and Fl-conA and an enhanced pattern of diffuse spots with Fl-WGA. Fl-SBA, however, showed a unique pattern on live myotubes which consisted of discrete, round spots and minimal uniform fluorescence. With shorter labeling times, Fl-SBA produced relatively more prominent uniform fluorescence on live myotubes. It appears, therefore, that the native distribution of SBA, conA and LCA-binding sites is similar and predominantly random on L6 myoblasts and myotubes, whereas some WGA-binding sites may be aggregated on myotubes. The results also suggest that SBA-binding sites readily cluster at 4 degrees C on myotubes but not myoblasts, whereas the other lectin sites undergo little or no redistribution on either cell type. Thus the mobility of SBA-binding sites may increase with differentiation.