M.K.R. Konda

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.

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.

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.

Mass spectrometric investigations on lactate adduction to equine myoglobin.

Research focused on determining the fundamental mechanisms by which lactate influences color stability has not considered a direct effect of lactate on myoglobin. Thus, the objective of this study was to use Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry to examine lactate adduction to myoglobin. Equine oxymyoglobin and equine carboxymyoglobin (0.15mM) were incubated with sodium lactate (200mM) at 4 degrees C, pH 5.6 in 50mM sodium citrate buffer or at 37 degrees C, pH 7.4 in 50mM sodium phosphate buffer, simulating typical meat storage and physiological conditions, respectively. Controls consisted of myoglobin plus a volume of deionized water equivalent to that used to deliver the lactate treatments. No peaks corresponding to lactate-Mb adducts could be detected in the mass spectra of samples incubated up to 360min at pH 7.4, 37 degrees C or 8days at pH 5.6 and 4 degrees C. Our results suggest that lactate did not form covalent adducts with equine oxy- and carboxy-myoglobin.

Effects of lactate-enhancement on surface reflectance and absorbance properties of beef longissimus steaks

A completely randomized block design was used to assess the effects of lactate-enhancement on surface reflectance and absorbance properties of beef longissimus steaks. Loins were divided into sections, assigned to one of four treatments (non-enhanced day 0, non-enhanced day 5, water-enhanced, and 3% lactate), vacuum packaged, stored for 5 days at 4 degrees C, and then cut into steaks that were used to prepare 100% of deoxy-, oxy-, met-, and carboxymyoglobin according to AMSA (1991). Surface color was analyzed using a HunterLab Miniscan Plus Spectrocolorimeter. Lactate-enhanced steaks had the least overall surface reflectance and the darkest surface color (lower L*; P<0.05). For 100% of each myoglobin form, K/S values and ratios (isobestic wavelengths/525 nm) at 474, 525, 572, and 610 also were influenced by lactate-enhancement. Hence, when estimating surface myoglobin forms using K/S ratios, separate 100% myoglobin reference standards should be prepared from both non-enhanced and enhanced steaks.

Species‐Specific Effects of Sarcoplasmic Extracts on Lipid Oxidation in vitro

The degree to which lipid and myoglobin (Mb) oxidation processes interact in meat can be species-specific. We investigated the effects of beef and pork sarcoplasmic extracts containing different Mb concentrations on lipid oxidation in a liposome system. Sarcoplasm was extracted from beef and pork longissimus dorsi and psoas major muscles. Beef sarcoplasm was diluted with 0.1 M phosphate buffer to obtain a Mb concentration equivalent to that in pork sarcoplasm. Conversely, equine heart Mb was added to pork sarcoplasm to match the myoglobin concentration of beef sarcoplasm. This resulted in beef and pork sarcoplasms, each with 2 different Mb concentrations for the longissimus (0.02 mM and 0.07 mM) and psoas (0.05 and 0.12 mM). Sarcoplasm (or phosphate buffer control) was incorporated within a phosphatidylcholine liposome preparation and incubated at 25 degrees C. Thiobarbituric acid reactive substances (TBARS) were measured at 0, 30, 60, 90, and 120 min of incubation. Regardless of species, greater Mb concentration within the sarcoplasm increased lipid oxidation (P < 0.05). Across muscles, pork sarcoplasm had lower TBARS values than beef sarcoplasm (P < 0.05). Our results suggest that pork sarcoplasm has a lesser effect on lipid oxidation than beef sarcoplasm for a common Mb concentration. However, increased myoglobin concentration within sarcoplasm promotes lipid oxidation regardless of species.