Cysteine, sodium metabisulfite, and glutathione enhance crosslinking between proteins during high moisture meat analog extrusion processing and may improve the fibrousness of the products.

BACKGROUND: High moisture meat analog (HMMA) products processed using extrusion have become increasingly popular in the last few years. Because the formation of disulfide bonds is believed to play a critical role in the texturization mechanism, this study aimed to understand how chemical compounds capable of reducing disulfide bonds, specifically cysteine, sodium metabisulfite, and glutathione, affect the texture and the chemical interactions between the proteins. METHOD: Wheat protein blended with cysteine, sodium metabisulfite, or glutathione at levels of 0, 0.5, 1.0, 2.5, 5.0, and 7.5 g kg-1 was extruded at three different temperatures (115, 140, and 165 °C) using a co-rotating twin-screw extruder. The feed rate (85 g min-1), the moisture content (600 g kg-1), and the screw speed (300 rpm) were kept constant. Unextruded and extruded material was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, polymeric protein fractionation, and sulfhydryl group/disulfide bond analysis. Extruded samples were further analyzed for their hardness and their anisotropic index. RESULTS: The inclusion of reductants significantly affected the structure of the obtained extrudates. Although reducing agents had a relatively small impact on the total amount of disulfide bonds, their action significantly enhanced crosslinking between the proteins. At select conditions, samples with high fibrousness were specifically obtained when cysteine or sodium metabisulfite was included at levels of 5.0 g kg-1. DISCUSSION: In the presence of reducing agents, it is believed that disulfide bonds are split earlier during the process without binding to them, giving the protein strands more time to unravel and align, leading to a better flow behavior and more fibrous products. © 2024 Society of Chemical Industry.

Mitochondrial Degeneration, Depletion of NADH, and Oxidative Stress Decrease Color Stability of Wet-Aged Beef Longissimus Steaks.

Interrelationship between mitochondria and myoglobin function influence beef color. NADH level in postmortem muscle is an important determinant of mitochondrial activity and metmyoglobin reduction. Increased aging time promotes discoloration of steaks; however, the mechanism of this effect is not clear. The objective was to characterize the role of wet-aging in beef longissimus lumborum muscle mitochondrial function and to characterize the global metabolome to determine the mechanism of that can regenerate NADH. Beef longissimus lumborum muscles were randomly assigned to 3, 7, 14, 21, and 28 days aging periods. Surface color, biochemical, mitochondrial, and metabolite profiles were determined at each aging period and at the end of 6-day display. During 6-day display, sections aged for 28 days had 30.4% decrease in redness than sections aged for 3 days. Aging time decreased (P <0.05) muscle oxygen consumption, mitochondrial protein content, and antioxidant capacity. Metabolites such as fumaric acid, creatinine, and fructose, that can take part in glycolytic/TCA cycle and regenerate NADH decreased (P <0.05) with aging and display time. In support, NADH levels also decreased (P <0.05) with aging time, but aging time had no effect (P = 0.44) on NADH-dependent reductase activity. The results suggest that decreased color stability in aged beef can be attributed to increased mitochondrial damage, depletion of metabolites that can regenerate NADH, and increased oxidative stress. PRACTICAL APPLICATION: Beef aging time results in increased discoloration of steaks under retail display. The current research determines the fundamental basis of lower color stability in aged beef. The results indicate that mitochondrial degeneration, depletion of metabolites that produce NADH, and increased oxidative stress can limit shelf-life of aged steaks. Hence, application of post-harvest strategies to minimize mitochondrial damage and oxidative changes may have the potential to increase shelf-life of aged beef.

Novel nitrite-embedded packaging improves surface redness of dark-cutting longissimus steaks.

The objective of this research was to determine the effects of nitrite-embedded/FreshCase packaging on lean color of dark-cutting beef. Eight dark-cutting (pH > 6.0) and eight USDA Low Choice (normal-pH; mean pH = 5.6) beef strip loins (longissimus lumborum) were selected 3 day after harvest. Each dark-cutting loin was sliced into five 2.5-cm thick steaks and randomly assigned to 1) dark-cutting steak packaged in polyvinyl chloride film (PVC) overwrap, 2) dark-cutting steak packaged in nitrite-embedded film, 3) dark-cutting steaks dipped in 0.2% rosemary solution and packaged in nitrite-embedded film, and 4) dark-cutting steak dipped in deionized water and packaged in nitrite-embedded film. The fifth dark-cutting steak was used to determine pH and proximate composition. Normal-pH choice loins were used as a control and each loin was randomly assigned to either PVC overwrap for retail display or to determine pH and proximate composition. Packages were placed in coffin-style retail display cases under continuous fluorescent lighting for 3 days. A HunterLab MiniScan XE Plus spectrophotometer was utilized to characterize steak color every 24 h. There was a significant treatment × storage time interaction (P < 0.05) for a* values and nitric oxide myoglobin formation. On days 1, 2, and 3 of the display, nitrite-embedded treatment improved (P < 0.05) redness compared to other dark-cutting steaks in PVC. A 45% increase in redness (P < 0.05) was observed for nitrite-embedded rosemary treatment over dark-cutting steak in PVC on day 3 of display. Nitric oxide myoglobin formation on day 0 was less for all dark-cutting steaks in nitrite-embedded packaging. Metmyoglobin content was greater (P < 0.05) on day 0 for dark-cutting steaks packaged in nitrite-embedded treatments than dark-cutting steaks in PVC. However, metmyoglobin level in dark-cutting steaks packaged in nitrite-embedded treatments decreased (P < 0.05) on day 1 compared with day 0. Dark-cutting steaks packaged in PVC had greater (P < 0.05) L* values on day 0 than other dark-cutting steaks in nitrite-embedded packaging. Conversely, on days 1, 2, and 3, there were no differences (P > 0.05) in L* values between dark-cutting treatments. Dark-cutting steaks in nitrite-embedded packaging had lower total plate count (P < 0.05) than dark-cutting steak packaged in PVC. The current research indicated that nitrite-embedded packaging has the potential to improve surface color of dark-cutting beef.

Presence of oxygen and mitochondria in skeletal muscle early postmortem.

Anaerobic glycolysis dominates energy metabolism postmortem. Even so, however, recent studies suggest mitochondria can modify postmortem energy metabolism and may contribute to pH decline, possibly affecting the transformation of muscle to meat and fresh meat quality development. Because oxygen is a necessary component of mitochondrial function, oxygenation of porcine and bovine longissimus thoracis et lumborum was determined postmortem using NIR spectroscopy. The ratio of oxy- to deoxymyoglobin decreased with time postmortem in both species. Metabolic analyses of muscle samples collected over the same timeframe also revealed fluctuations in TCA intermediates. Finally, mitochondria collected from muscle of electrically stimulated carcasses differed from those of non-stimulated muscle. Collectively, these data support the thesis that muscle mitochondria function early postmortem and may play a more active part in pH decline and possibly meat quality development.

Effects of Muscle-Specific Oxidative Stress on Cytochrome c Release and Oxidation-Reduction Potential Properties.

Mitochondria play a significant role in beef color. However, the role of oxidative stress in cytochrome c release and mitochondrial degradation is not clear. The objective was to determine the effects of display time on cytochrome c content and oxidation-reduction potential (ORP) of beef longissimus lumborum (LL) and psoas major (PM) muscles. PM discolored by day 3 compared with LL. On day 0, mitochondrial content and mitochondrial oxygen consumption were greater in PM than LL. However, mitochondrial content and oxygen consumption were lower (P < 0.05) in PM than LL by day 7. Conversely, cytochrome c content in sarcoplasm was greater on days 3 and 7 for PM than LL. There were no significant differences in ORP for LL during display, but ORP increased for PM on day 3 when compared with day 0. The results suggest that muscle-specific oxidative stress can affect cytochrome c release and ORP changes.

The Draft Genome Sequence of Xanthomonas sp. Strain Mitacek01 Expands the Pangenome of a Genus of Plant Pathogens.

We report the draft genome sequence of Xanthomonas sp. strain Mitacek01, isolated from an indoor environment vending machine surface with frequent human use in Stillwater, Oklahoma, USA, as part of the Student-Initiated Microbial Discovery project. The genome has a total size of 3,617,426 bp and a contig N50 of 1,906,967 bp.