R. Ramanathan

Packaging-specific influence of chitosan on color stability and lipid oxidation in refrigerated ground beef.

We examined the influence of chitosan on lipid oxidation and color stability of ground beef stored in different modified atmosphere packaging (MAP) systems. Ground beef patties with chitosan (1%) or without chitosan (control) were packaged either in high-oxygen MAP (HIOX; 80% O(2)+20% CO(2)), carbon monoxide MAP (CO; 0.4% CO+19.6% CO(2)+80% N(2)), vacuum (VP), or aerobic packaging (PVC) and stored at 1 °C. Chitosan increased (P<0.05) redness of patties stored in PVC and CO, whereas it had no effect (P>0.05) in HIOX. Chitosan patties demonstrated lower (P<0.05) lipid oxidation than controls in all packaging. Control patties in PVC and HIOX exhibited greater (P<0.05) lipid oxidation than those in VP and CO, whereas chitosan patties in different packaging systems were not different (P>0.05) from each other. Our findings suggested that antioxidant effects of chitosan on ground beef are packaging-specific.

Effect of carbon monoxide packaging and lactate enhancement on the color stability of beef steaks stored at 1°C for 9 days.

Our objective was to assess the effects of lactate enhancement in combination with different packaging systems on beef longissimus lumborum and psoas major steak color. Strip loins and tenderloins (n=16) were assigned to one of four injection treatments (non-injected control, water-injected control, 1.25%, and 2.5% lactate in the finished product). Steaks were individually packaged in either vacuum, high-oxygen (80% O(2)/20% CO(2)), or 0.4% CO (30% CO(2)/69.6% N(2)) and stored for either 0, 5, or 9 days at 1°C. The L(∗) and a(∗) values of both the longissimus and psoas responded similarly to lactate, which at 2.5% darkened steaks (P<0.05) packaged in all atmospheres and improved (P<0.05) the redness of steaks packaged in high-oxygen. Packaging steaks in CO did not counteract the darkening effects of lactate. Nevertheless, CO improved (P<0.05) color stability compared with high-oxygen packaging.

Sodium lactate influences myoglobin redox stability in vitro.

Injection-enhancement of beef with lactate improves color stability; however, the mechanism is unclear. Thus, our objectives were to assess the effects of sodium lactate on equine myoglobin redox stability in vitro. Oxymyoglobin at pH 5.6 (50mM sodium citrate) and pH 7.4 (50mM sodium phosphate) was incubated at 4°C with lactate (0, 5, 10, 100, or 200mM) and myoglobin redox form was determined using absorbance spectra. Metmyoglobin formation at pH 5.6 and 7.4 was significantly (P<0.05) decreased by lactate at concentrations of 100 and 200mM. In general, increasing lactate concentration from 100 to 200mM increased (P<0.05) oxymyoglobin redox stability. This effect of lactate on myoglobin redox stability could be partially responsible for the improved color stability associated with lactate injection-enhanced beef products. Further work should determine the effect of lactate on beef myoglobin.

Enhancing the thermal destruction of Escherichia coli O157:H7 in ground beef patties by trans-cinnamaldehyde.

The effect of trans-cinnamaldehyde (TC) on the inactivation of Escherichia coli O157:H7 in undercooked ground beef patties was investigated. A five-strain mixture of E. coli O157:H7 was inoculated into ground beef (7.0log CFU/g), followed by addition of TC (0, 0.15, and 0.3%). The meat was formed into patties and stored at 4 degrees C for 5 days or at -18 degrees C for 7 days. The patties were cooked to an internal temperature of 60 or 65 degrees C, and E. coli O157:H7 was enumerated. The numbers of E. coli O157:H7 did not decline during storage of patties. However, cooking of patties containing TC significantly reduced (P<0.05) E. coli O157:H7 counts, by >5.0log CFU/g, relative to the reduction in controls cooked to the same temperatures. The D-values at 60 and 65 degrees C of E. coli O157:H7 in TC-treated patties (1.85 and 0.08min, respectively) were significantly lower (P<0.05) than the corresponding D-values for the organism in control patties (2.70 and 0.29min, respectively). TC-treated patties were more color stable and showed significantly lower lipid oxidation (P<0.05) than control samples. TC enhanced the heat sensitivity of E. coli O157:H7 and could potentially be used as an antimicrobial for ensuring pathogen inactivation in undercooked patties. However detailed sensory studies will be necessary to determine the acceptability to consumers of TC in ground beef patties.

Effects of postmortem storage time on color and mitochondria in beef.

To assess the effects of aging time (0, 15, 30, and 45 d) and temperature (0 or 5 °C) on beef mitochondria and steak color, vacuum packaged longissimus (n=15) and cardiac muscles were assigned to 1 of 6 temperature×time combinations. As time increased, initial red color intensity increased whereas both mitochondrial oxygen consumption and color stability decreased. The decrease in mitochondrial oxygen consumption associated with longer aging times will increase initial color intensity. However, this improvement in color development will be negated by the decreased color stability that results from the effects of storage on mitochondria.

Effect of lactate-enhancement, modified atmosphere packaging, and muscle source on the internal cooked colour of beef steaks

Earlier studies on lactate-mediated colour stability in beef did not address the possible influence on cooked colour. Our objective was to examine the effect of lactate-enhancement, muscle source, and modified atmosphere packaging (MAP) on the internal cooked colour of beef steaks. Longissimus lumborum (LL) and Psoas major (PM) muscles from 16 (n=16) beef carcasses (USDA Select) were randomly assigned to 4 enhancement treatments (non-injected control, distilled water-enhanced control, 1.25% and 2.5% lactate), and fabricated into 2.54-cm steaks. Steaks were individually packaged in either vacuum (VP), high-oxygen MAP (HIOX; 80% O(2)+20% CO(2)), or carbon monoxide MAP (CO; 0.4% CO+19.6% CO(2)+80% N(2)), and stored for 0, 5, or 9 days at 1°C. At the end of storage, surface and internal colour (visual and instrumental) was measured on raw steaks. Steaks were cooked to an internal temperature of 71°C, and internal cooked colour (visual and instrumental) was evaluated. Lactate-enhancement at 2.5% level resulted in darker (P<0.05) cooked interiors than other treatments. Interior cooked redness decreased (P<0.05) during storage for steaks in VP and HIOX, whereas it was stable for steaks in CO. Our findings indicated that the beef industry could utilise a combination of lactate-enhancement and CO MAP to minimise premature browning in whole-muscle beef steaks.

Species-specific Myoglobin Oxidation

The effect of the lipid oxidation product, 4-hydroxy-2-nonenal (HNE), on oxidation of oxymyoglobin (OxyMb) from seven different meat-producing species was investigated. Relative to controls, HNE increased OxyMb oxidation within all species (p < 0.05) at both 25 and 4 °C, pH 5.6. The relative effect of HNE was greater for myoglobins (Mbs) that contained 12 ± 1 histidine (His) residues than for those that contained 9 His residues (p < 0.05); HNE efficacy in all species except chicken and turkey decreased with time. Mono-HNE adducts were detected in all species except chicken and turkey. In general, HNE alkylation increased the Mbs ability to accelerate lipid oxidation in a microsome model. However, neither an HNE nor a Mb species dependent effect was observed. Results suggested that microsome model system associated lipid oxidation overshadowed HNE and species effects on OxyMb oxidation observed in lipid-free systems.

Effects of lactate on beef heart mitochondrial oxygen consumption and muscle darkening.

The mechanism of lactate-induced beef color darkening is unclear. Our objective was to evaluate the ability of mitochondria isolated from bovine cardiac muscle to utilize lactate as a fuel for respiration. Addition of lactate (4, 8, and 16 mM) to isolated bovine cardiac mitochondria resulted in state IV oxygen consumption at pH 7.2 and 25 degrees C measured using a Clark oxygen electrode. Combining mitochondria with lactate, LDH, and NAD increased state IV oxygen consumption compared with that of lactate alone (p < 0.05). Moreover, oxygen consumption resulting from the addition of lactate-LDH-NAD (0.2 mM each) was comparable to oxygen consumption resulting from the direct addition of NADH (0.2 mM) to mitochondria at pH 7.2. Rotenone reduced (p < 0.05) lactate-mediated darkening in bovine cardiac muscle homogenates. Lactate-induced beef color darkening may be due to increased oxygen consumption by mitochondria, which out-competes myoglobin for oxygen and results in dark colored muscle.

Color-stabilizing effect of lactate on ground beef is packaging-dependent.

Previous research on lactate-induced color stability in ground beef did not address the potential influence of packaging. The objective of the present study was to examine the effects of lactate on the color stability of ground beef patties stored in different modified atmosphere packaging (MAP) systems. Ground beef patties with either 2.5% potassium lactate or no lactate were packaged in vacuum (VP), high-oxygen MAP (HIOX; 80% O(2)+20% CO(2)), carbon monoxide MAP (CO; 0.4% CO+19.6% CO(2)+80% N(2)), or aerobic packaging (PVC) and stored for 0, 2, or 4 days at 2 degrees C. Lactate-treated patties were darker (P<0.05; lower L * values) than control patties. Surface redness (a * values) was greater (P<0.05) for lactate patties than the controls when stored in PVC, HIOX, and VP. However, lactates effects on a * values were not evident when packaged in CO (P>0.05). The color-stabilizing effect of CO could have masked lactates effect on surface redness. While lactate patties in PVC and VP demonstrated lower (P<0.05) discoloration than controls, no differences (P>0.05) existed between controls and lactate samples in CO and HIOX. Our results indicated that the effects of lactate on ground beef color are dependent on packaging.

Effects of lactate and modified atmospheric packaging on premature browning in cooked ground beef patties.

Our objectives were to determine the effects of lactate and modified atmosphere packaging on raw surface color, lipid oxidation, and internal cooked color of ground beef patties. Eight chubs (85% lean) were divided in half and each half was either assigned to the control (no lactate) or mixed with 2.5% lactate (w/w). Following treatment, patties were prepared and packaged in either vacuum, PVC (atmospheric oxygen level), high-oxygen (80% O(2)+20% CO(2)), or 0.4% CO (30% CO(2)+69.6% N(2)) and stored for 0, 2, or 4days at 2 degrees C. After storage, raw surface color and lipid oxidation were measured and patties were cooked to either 66 degrees C or 71 degrees C. Lactate improved (p<0.05) color stability of PVC, high-oxygen, and vacuum packaged raw patties, but had no effect (p>0.05) on the a * values and visual color scores of patties in 0.4% CO. Lactate decreased (p<0.05) lipid oxidation in all packaging atmospheres. Nevertheless, high-oxygen and PVC-packaged patties had more (p<0.05) lipid oxidation than patties in CO and vacuum. Lactate had no effect (p>0.05) on premature browning, whereas patties packaged in high-oxygen demonstrated premature browning. Conversely, cooked patties in 0.4% CO and vacuum were more red (p<0.05) than both high-oxygen and PVC-packaged patties. Although lactate improved raw color stability, it did not minimize premature browning in cooked ground beef patties.