pH Of Beef Research Articles

Study on Meat Discoloration Based on Storage Effect and pH Factor Using Square Wave Voltammetry

The overarching objective of this project is to discover the electrochemical features of meat discoloration under various point-of-sale meat conditions. The bright red color of meat plays a key role in influencing consumers to purchase meat. The discoloration of meat is causing high economic loss around the globe. Here, we used a square wave technique to observe redox peaks in beef sarcoplasm with the incubation time to diagnose discoloration focusing on the point of sale. The first investigation was centered on the storage effect on discoloration where normal pH beef sarcoplasm (post mortem) showed a rising trend of peaks that correspond with a growing accumulation of metmyoglobin and decumulation of oxymyoglobin intensifying the rate of discoloration. The second study was done by comparing discoloration of beef meat at two pH conditions, pH 7.4 (physiological state) and pH 6.4 (stressed animal muscle). Notably, a substantial elevation in the oxidation peak signal was observed from the pH 6.4 sample compared to the pH 7.4 counterpart, with discoloration. Furthermore, the UV spectral absorbance of meat samples was used to calculate the percentage of oxy- and metmyoglobin contents to gain independent insights. From these studies, we can gain a fundamental understanding of the redox processes of beef upon discoloration and thus develop novel tools to detect meat spoilage and discoloration rates. Keywords: Beef sarcoplasm, square wave voltammetry, metmyoglobin, oxymyoglobin

In-depth exploration of the high and normal pH beef proteome: First insights emphasizing the dynamic protein changes in Longissimus thoracis muscle from pasture-finished Nellore bulls over different postmortem times

This study aimed to evaluate for the first time the temporal dynamic changes in early postmortem proteome of normal and high ultimate pH (pHu) beef samples from the same cattle using a shotgun proteomics approach. Ten selected carcasses classified as normal (pHu < 5.8; n = 5) or high (pHu ≥ 6.2; n = 5) pHu beef from pasture-finished Nellore (Bos taurus indicus) bulls were sampled from Longissimus thoracis muscle at 30 min, 9 h and 44 h postmortem for proteome comparison. The temporal proteomics profiling quantified 863 proteins, from which 251 were differentially abundant (DAPs) between high and normal pHu at 30 min (n = 33), 9 h (n = 181) and 44 h (n = 37). Among the myriad interconnected pathways regulating pH decline during postmortem metabolism, this study revealed the pivotal role of energy metabolism, cellular response to stress, oxidoreductase activity and muscle system process pathways throughout the early postmortem. Twenty-three proteins overlap among postmortem times and may be suggested as candidate biomarkers to the dark-cutting condition development. The study further evidenced for the first time the central role of ribosomal proteins and histones in the first minutes after animal bleeding. Moreover, this study revealed the disparity in the mechanisms underpinning the development of dark-cutting beef condition among postmortem times, emphasizing multiple dynamic changes in the muscle proteome. Therefore, this study revealed important insights regarding the temporal dynamic changes that occur in early postmortem of high and normal muscle pHu beef, proposing specific pathways to determine the biological mechanisms behind dark-cutting determination.

The relationship between pH of pH-model beef and impedance measured using touch-type electrodes.

Meat pH affects its color, texture, and water-holding capacity; however, a method for nondestructively distinguishing high-pH from normal-pH meat is unknown. We investigated the method of preparing an extensive pH-model of beef immersed in different pH buffers and the relationship between pH of the pH-model beef and impedance, measured using touch-type electrodes. The results showed that a model beef of pH 4.91-6.39 could be obtained when a beef steak (pH 5.68) was immersed in a solution of pH 4.0-7.0. In addition, we found a significant negative correlation between immersion pH and drip loss, and between immersion pH and impedance measured at 50 kHz (P < 0.01). These results provide an estimation equation (y = -16.5x + 195.3) that can be used to nondestructively determine the pH (x) of pH-model beef by measuring its impedance (y) using touch-type electrodes at 50 kHz (P < 0.01). Hence, the study shows the possibility of nondestructively estimating the pH of pH model beef by measuring impedance using touch-type electrodes.

Exploratory lipidome and metabolome profiling contributes to understanding differences in high and normal ultimate pH beef

The aim of this work was to compare the lipidome and metabolome profiling in the Longissimus thoracis muscle early and late postmortem from high and normal ultimate pH (pHu) beef. Lipid profiling discriminated between high and normal pHu beef based on fatty acid metabolism and mitochondrial beta-oxidation of long chain saturated fatty acids at 30 min postmortem, and phospholipid biosynthesis at 44 h postmortem. Metabolite profiling also discriminated between high and normal pHu beef, mainly through glutathione, purine, arginine and proline, and glycine, serine and threonine metabolisms at 30 min postmortem, and glycolysis, TCA cycle, glutathione, tyrosine, and pyruvate metabolisms at 44 h postmortem. Lipid and metabolite profiles showed reduced glycolysis and increased use of alternative energy metabolic processes that were central to differentiating high and normal pHu beef. Phospholipid biosynthesis modification suggested high pHu beef experienced greater oxidative stress.

Valorisation of date seed powder (Phoenix dactylifera L.) for tenderizing properties of different types of meat

Recently, date (Phoenix dactylifera L.) seeds have gained much popularity due to their vast applications that benefit people and the environment, elevated with plenty of research on food product formulation, cosmetics, and medicinal supplements. Date seeds constitute 10-15% of the date fruit weight. Although date seeds are considered waste products, however, they contain many valuable substances such as carbohydrates, oil, dietary fibre, protein, bio-active polyphenol, tannin and natural antioxidants. Thus, valorisation of the date seeds is necessary as the value could be utilized maximally if they are being studied aptly. This study was intended to (i) evaluate the physical properties of beef and lamb in terms of texture, pH, colour, cooking loss, and water holding capacity as affected by date seed powder; and (ii) compare the tendering effect of date seed powder towards beef and lamb. Texture profile analysis indicated significant differences (p≤0.05) in terms of hardness, springiness, chewiness, and gumminess between the different amount of seed powder used in marinated beef and lamb. The lowest pH value belonged to 20 g of date seed powder which was 5.7 and 6.2 for beef and lamb, respectively. The colour of the lamb was found to be significantly different in terms of lightness, redness, and yellowness when date seed powder was used regardless of its amount. Both beef and lamb displayed a statistically significant (p≤0.05) reduction of colour (L*, a*, and b*) from 20 g treatment samples with 29.7 and 26.5, respectively over the control samples. For beef, redness and yellowness demonstrated a significant difference (p≤0.05) for 20 g treatment samples marinated with date seed powder. Both cooking loss and water holding capacity (WHC) was reduced as the amount of date seed powder used was increased. Different amounts of date seed powder affected the physical properties of beef and lamb, while 15 g and 20 g of date seed powder showed a positive result in regards to meat tenderness.

Proteome basis for the biological variations in color and tenderness of longissimus thoracis muscle from beef cattle differing in growth rate and feeding regime

The proteome basis for the biological variations in color and tenderness of longissimus thoracis muscle from ½ Angus (Bos taurus taurus) × ½ Nellore (Bos taurus indicus) crossbred steers was evaluated in a completely randomized experimental design consisting of four treatments (n = 9 per treatment): 1) feedlot finished, high growth rate (FH); 2) feedlot finished, low growth rate (FL); 3) pasture finished, high growth rate (PH); and 4) pasture finished, low growth rate (PL). The following comparisons were made to evaluate the effects of finishing systems and growth rates on muscle proteome: 1) FH × PL; 2) FL × PH; 3) FH × FL; and 4) PH × PL. Sixteen protein spots were differentially abundant among these comparisons (P ≤ 0.05), which were distinguished in two major clusters, energy metabolism- and muscle structure-related proteins that impacted glycolysis, carbon metabolism, amino acid biosynthesis and muscle contraction pathways (FDR ≤ 0.05). For FH × PL comparison, triosephosphate isomerase (TPI), phosphoglucomutase-1 (PGM1) and phosphoglycerate kinase 1 (PGK1) were overabundant in FH beef whereas troponin T (TNNT3), α-actin (ACTA1) and myosin regulatory light chain 2 (MYLPF) were overabundant in PL beef. For the FL × PH comparison, PGM1, phosphoglycerate mutase 2 (PGAM2) and annexin 2 (ANXA2) were overabundant in PH beef. For the FH × FL comparison, AMP deaminase (AMPD1) and serum albumin (ALB) were overabundant in FH beef whereas glycogen phosphorylase (PYGM) was overabundant in FL beef. For the PH × PL comparison, myoglobin (MB) was overabundant in PH beef whereas PYGM and MYLPF were overabundant in PL beef. In non-aged beef, L* was positively correlated with PGM1 (r = 0.54) while tenderness was negatively correlated with PGAM2 (r = -0.74) and ANXA2 (r = -0.60). In 7-d aged beef, color attributes (L*, a* and b*) were positively correlated with PGM1 (r = 0.67, 0.64 and 0.64, respectively) while tenderness was negatively correlated with TNNT3 (r = -0.57), PGK1 (r = -0.52) and MYLPF (r = -0.66). Therefore, finishing systems and growth rate affected the muscle proteome profile, which was related to beef color and tenderness. Additionally, these results suggest potential biomarkers for beef color (PGM1 and PGAM2) and tenderness (ANXA2, MYLPF, PGK1 and TNNT3).

New alternatives for improving and assessing the color of dark–cutting beef – a review

Myoglobin (Mb) is a sarcoplasmic heme protein present in muscle cells, which acts as a short–term oxygen (O2) reserve in the muscle tissue. After slaughtering and exsanguination, Mb is the major pigment that provides the red color in meat. The concentration of Mb together with its redox state are two pivotal factors that determine meat color. The elevated pH of dark–cutting beef can affect both physical and biochemical properties resulting in decreased oxygenation. The darkening observed in high ultimate pH (pHu) beef concerns meat processors as color is the initial attribute that impacts on the purchase. Thus, any atypical meat color (i.e., loss of brightness) reduces consumer interest in the product. Several studies have demonstrated that immunological castration is effective in preventing both aggressive behavior and undesirable dark–cutting of bull meat. However, little information is available on the effects of processing techniques that limit the oxidation of ferrous iron (Fe2+), Mb or promote metmyoglobin (MMb) reduction in dark–cutting beef. Because of the importance of color to fresh beef marketability, this review aimed at overviewing the significance of pHu in beef color and color stability and to discuss new alternatives for improving and assessing the beef color of dark–cutting beef, especially in Nellore bulls and their crossbreds, which are widely used in beef cattle production in Brazil.

Dry Aging of High Ultimate pH Beef

ObjectivesDry aging is a process in which water is removed from the meat by evaporation. As meat loses water, the flavor compounds are concentrated, resulting in stronger flavor. Meat pH may be important when dry aging as it relates to the ability of muscle to bind water. Therefore, this study aimed to evaluate pH effects on water loss when dry aging and the effects on meat quality characteristics. Dry aging of dark cutting (DC) beef may improve flavor and increase yield.Materials and MethodsSix USDA low Choice and six dark cutting (DC) carcasses with the same degree of marbling were selected and boneless strip loins from both sides were obtained. Longissimus muscle pH was measured, and carcasses were classified as DC (pH = 6.69), or control (pH = 5.47). Then, strip loins from each animal were assigned to 2 aging methods (wet or dry). The 4 treatments included 2 dry aging (DRY and DRY-DC) and 2 wet-aging treatments (WET and WET-DC). Dry aging occurred in individual dry-aging chambers at 50% relative humidity and 2200 RPM fan speed. The chambers (86 cm Length × 48 cm Width × 35 cm Height) have built-in weighing scales that can continuously monitor weight loss (± 5 g). Wet and dry-aged loins were aged in the same cooler for 45 d at 1°C.After aging, loins were fabricated into steaks and evaluated for trim loss, yield, tenderness (WBSF), color, discoloration, lipid oxidation, and sensory analysis (flavor) via triangle test (n = 32). Steaks assigned for color and lipid oxidation were placed under retail display (RD) at 2°C for 7 d. Rate of moisture loss and color data were analyzed as a split plot design with repeated measures. The TBARS data were analyzed as a split-plot design. All the other data were analyzed as a completely randomized design. Chamber (loin) was considered the experimental unit. Data were analyzed using the PROC GLIMMIX procedure of SAS with α = 0.05.ResultsWet-aged treatments had lower moisture loss, trim loss and higher yield than dry-aged treatments (P &lt; 0.05). However, no differences in rate of moisture loss (P = 0.51), total moisture loss (P = 0.96), trim loss (P = 0.69), or yield (P = 0.75) between DRY-DC and DRY were found. There were no differences among treatments for WBSF (P = 0.67). In general, DRY-DC and WET-DC steaks had the lowest lightness (L*) values, redness (a*) values (Fig. 3a), and yellowness (b*) values over the first 5 d of RD (P &lt; 0.05). Discoloration scores for DC steaks remained low throughout the RD period (Fig. 3b). DRY steaks had greater TBARS values than any other treatment at 0 d RD. At 4 and 7 d of RD, DRY-DC and WET-DC steaks had the lowest TBARS values, DRY steaks had the highest, while WET was intermediate (P &lt; 0.001). Results from the triangle test indicated a detectable difference between DRY-DC versus DRY (P = 0.01), DRY-DC versus WET-DC (P = 0.01), DRY-DC versus WET (P = 0.01), and WET-DC versus WET (P &lt; 0.01). Panelists frequently made unsolicited comments which suggested inferior eating satisfaction associated with DC flavor (wet or dry), although they were not asked questions regarding preference.ConclusionUltimate pH did not affect the rate and total moisture loss in dry aged beef. Results suggest that neither yield nor flavor were positively affected by dry aging of DC beef.Figure 3.a) Effect of ultimate pH (Dark cutters [DC] vs. Normal) and aging method (Wet vs. Dry) on objective redness (a*) values of strip loins steaks aged for 45 d through 7 d of retail display. b) Effect of ultimate pH (Dark cutters [DC] vs. Normal) and aging method (Wet vs. Dry) on discoloration (%) of strip loins steaks aged for 45 d through 7 d of retail display. a-c Means within a day with different superscripts are different (P &lt; 0.005).

Dry Aging of High Ultimate pH Beef

Dry Aging of High Ultimate pH Beef

Carbon monoxide packaging shows the same color improvement for dark cutting beef as high oxygen packaging

In this study, carbon monoxide (CO) modified atmosphere packaging (MAP) was used to increase redness (a*) and lightness (L*) values of dark cutting beef (ultimate pH (pHu)≥6.10), compared to normal pHu beef and intermediate pHu beef (pH: 5.40–5.79; pH: 5.80–6.09, respectively) during 20 d chilled storage. Compared with HiOx-MAP, CO-MAP exhibited similar color improvement effects (increased L*, a*, b* values) for all pHu beef groupings. The metmyoglobin (MetMb) content was lower under CO-MAP than that of HiOx-MAP in normal pHu beef, but opposite effects were observed in dark, high pH beef. This result could not be explained by MetMb reducing ability (MRA) and lipid oxidation, as both parameters were higher in CO-MAP beef than either normal or high pHu beef, compared with HiOx-MAP. In conclusion, CO-MAP was effective to maintain the cherry red color for dark cutting beef, but the color improvement mechanisms might be different with HiOx packaging methods.

Evaluation of Meat Quality on High pH Strip Loins Injected with Buffered Acetic Acid

This experiment evaluated the effects of injection of buffered vinegar [e(Lm)inate V, Hawkins Inc., Minneapolis, MN] at pH 5.0 on quality attributes of high pH beef strip loins. Strip loins (n = 16) were sectioned and treatments assigned to evenly represent each section, and on d 6 after harvest and fabrication treatments were injected into each section using a multi needle injector. One control and three treatments were used: 0 (T0), 0.4 (T0.4), 1.2 (T1.2), and 1.6% (T1.6) of the green weight of steaks was injected, and quality characteristics of strip loins were evaluated. Sections were then vacuumed packaged for an additional 3 d to simulate transport to retail outlets, then fabricated into steaks and overwrapped for an addition 3 d for simulation of retail storage. High pH control (T0) final pH (FpH) values were the highest, with a pH of 5.87. While there were similarities between treatments, overall as percentage of injection increased, FpH decreased. There was no difference among location (P &gt; 0.05) when evaluating FpH. There were no difference in cook loss or TBARS for location or treatment. Drip loss was greatest for T1.2 injection and in the most caudal section. Warner-Bratzler shear force (WBSF) was different due to the location of the section (P ≤ 0.05), with section Y (the third section) having the greatest value. Off flavor intensity increased (P ≤ 0.05) as percentage of injection increased. Final L*, a*, and b* values were different (P ≤ 0.05) for treatment levels in the loins with the control having the lowest L* and b* values. While this product was sufficient at altering final raw color and pH, it may not be feasible for industry use, due to minimal impacts on drip loss, cook loss, oxidation, and sensory characteristics with an increase in off flavor. Nonetheless, investigation of application with an antioxidant and/or functional ingredient could prove beneficial for industry use.

Effects of aging on the fundamental color chemistry of dark-cutting beef.

The objective of the current study was to evaluate the effects of aging on myoglobin chemistry of dark-cutting beef. Ten USDA Choice (mean pH = 5.6; normal pH beef) and 10 no-roll dark cutter (mean pH = 6.4) strip loins were obtained from a commercial packing plant within 3 d of harvest. Loins were cut into 4 sections, vacuum packaged, randomly assigned to 0-, 21-, 42-, and 62-d aging at 2°C in the dark. Following aging, loin sections were cut into 2.5-cm-thick steaks and were used to determine bloom development, oxygen consumption (OC), metmyoglobin reducing activity (MRA), and lipid oxidation. Surface color readings were measured using a HunterLab Miniscan XE Plus spectrophotometer. A significant muscle type × aging time interaction resulted for OC ( < 0.001). Normal pH steaks declined more ( < 0.001) in OC during aging than dark-cutting beef. On d 0, dark-cutting beef had a greater OC ( < 0.001) than normal pH beef. There was a significant muscle type × oxygenation time × aging period interaction for L* values, deoxymyoglobin (DeoxyMb), and oxymyoglobin (OxyMb). When dark-cutting sections were aged for 62 d, both 0 and 60 min bloom development L* values were greater ( < 0.0001) than 0 min dark-cutting sections aged for 21 or 42 d. At all aging periods, normal pH beef had greater OxyMb content and lower DeoxyMb ( < 0.0001) during bloom development than dark-cutting beef. An aging period × muscle type interaction was significant for % overall reflectance ( = 0.0017) and absorbance ( = 0.0038). Dark cutting and normal pH beef loin sections aged for 62 d had greater reflectance ( < 0.0001) than 21 d. On d 0, dark-cutting beef had greater ( < 0.0001) MRA than normal pH beef. There were no significant ( = 0.14) differences in MRA between 42 and 62 d between dark-cutting and normal pH beef. Dark cutting steaks had lower thiobarbituric acid reactive substances values ( < 0.0001) than normal pH steaks. The results indicate that characterizing the myoglobin chemistry during aging will help to design strategies to improve appearance of high pH beef.

Factors influencing the occurrence of high ultimate pH in three muscles of lamb carcasses in Australia

Chilled lamb meat exported from Australia has, on occasions, been rejected by importing countries due to greening, after only 6 weeks of storage time. Greening is known to be more prevalent in high ultimate pH (pHu) beef meat (&gt;5.9). There are few data available for lamb carcasses in Australia on the occurrence of high pHu meat, which may have an impact on the understanding and control of quality and greening during storage. The aim of this project was to determine the prevalence of, and influencing factors for, high pHu meat in a range of muscle types in lamb carcasses in Australia. Muscle pHu data were collected from a total of 1614 carcasses from 78 lots at four lamb processing plants in Victoria and New South Wales in autumn and spring of 2013. The pHu of the knuckle (rectus femoris), rack (longissimus) and blade (infraspinatus) was measured and data on carcass and lot characteristics were recorded. Data were subjected to restricted maximum likelihood and generalised linear mixed model analysis. The mean pHu of the knuckle, rack and shoulder were 6.06, 5.79 and 6.12 respectively, and the main factors influencing muscle pHu and occurrence of dark-cutting were breed, season, electrical stimulation and carcass weight. Merino lambs had a higher pHu in the blade and knuckle than did other breeds (P &lt; 0.05, P &lt; 0.01 respectively). Lambs processed in autumn had a higher predicted pHu in the blade and knuckle and a higher percentage dark-cutting (DC; pHu &gt;6.0) for those muscles, than did those processed in spring (P &lt; 0.05). Carcasses that had been electrically stimulated had a higher %DC and a higher pHu in all three muscles (P &lt; 0.05). Carcass weight had a significant effect on the pHu of all three muscles (P &lt; 0.001), with heavier carcasses having a lower pHu and lower %DC. The pHu of the rack was not a reliable predictor for the pHu in other muscles of the lamb carcass. In conclusion, the high occurrence of DC in the muscles, particularly the blade and knuckle, suggests that these muscles may be at risk for producing greening in the vacuum bag during storage.

Effects of meat pH and the initial numbers of spores of Clostridium estertheticum on the development of blown pack spoilage of vacuum‐packaged beef

SummaryTo understand how the initial numbers of Clostridium estertheticum spores on, and the concentration of glucose in meat affect the development of blown pack spoilage, beef of pH ≤5.6 and of pH ≥5.8 was inoculated with the spores at various numbers, vacuum‐packaged and stored at 2 °C. For beef of pH ≤5.6, the volumes of packs inoculated with ≤10 spores did not change; and packs inoculated with ≥30 spores started swelling after 35 days, and the rate of volume increase increased with increasing number of inoculated spores. For beef of pH ≥5.8, packs inoculated 0, three or ten spores slackened, and packs inoculated with ≥30 spores became swollen at the end of storage, but to a much lesser degree than the corresponding packs of beef of pH ≤5.6. Glucose was reduced by 21 mm and depleted in the rinse fluids from swollen packs of beef of pH ≤5.6 and of pH ≥5.8, respectively.

Effects of meat pH on growth of 11 species of psychrotolerant clostridia on vacuum packaged beef and blown pack spoilage of the product

The aim of the study was to determine the effects of meat pH on the abilities of 11 psychrotolerant Clostridium spp. to grow on, and to possibly cause blown pack spoilage of vacuum packaged beef. Beef steaks of pH 5.4–5.6, 5.7–5.9 or ≥6.0, i.e. of normal, intermediate or high pH were prepared and vacuum packaged. Groups of 3 steaks of the same pH range were inoculated with log phase cultures of Clostridium algoriphilum, Clostridium algidixylanolyticum, Clostridium bowmanii, Clostridium estertheticum, Clostridium frigoris, Clostridium frigidicarnis, Clostridium gasigenes, Clostridium lacusfryxellense, Clostridium psychrophilum, Clostridium tagluense or Clostridium vincentii. Each pack was resealed immediately after the steak was inoculated, and pack volumes were determined by water displacement, immediately after resealing and at intervals during storage at 2 °C for 56 days. All of the clostridia grew in packs of high pH beef but none caused pack swelling. Packs of intermediate pH beef inoculated with C. estertheticum began to swell after 14 days, with a mean rate of increase of pack volumes of 6.80 ml/day. One pack of intermediate pH beef inoculated with C. frigoris was swollen after 37 days. Packs of normal pH beef that had been inoculated with C. estertheticum began swelling after 14 days with a mean rate of increase of pack volumes of 7.70 ml/day. Packs of normal or intermediate pH beef inoculated with other clostridia did not swell. After storage, the numbers of most Clostridium spp., as determined by real-time PCR were greater on beef of high pH than of lower pH values, but the numbers of C. frigidicarnis and C. lacusfryxellense were highest on intermediate pH meat, the numbers of C. estertheticum were higher on meat of lower than of high pH, and the numbers of C. tagluense were the same on meat of all pH values. With high pH meat, glucose was reduced to very low level in rinse fluids from packs that had been inoculated with any Clostridium sp. With intermediate and normal pH meat, glucose was reduced to very low concentrations in only rinse fluids from beef that had been inoculated with C. estertheticum.

Effects of the initial numbers of spores of Clostridium estertheticum on the development of blown pack spoilage of vacuum packaged beef of normal and intermediate pH

Effects of the initial numbers of spores of Clostridium estertheticum on the development of blown pack spoilage of vacuum packaged beef of normal and intermediate pH

Lactic acid enhancement can improve the fresh and cooked color of dark-cutting beef1,2

Two experiments were conducted to compare the effects of enhancing dark-cutting (DC) strip loins with lactic acid (LAC) on fresh and cooked beef color, as well as sensory attributes, with nonenhanced, normal pH strip loins (CH). Strip loins, with an average ultimate pH of 6.70 ± 0.11 (Exp. 1) and 6.78 ± 0.11 (Exp. 2), were cut into 2 equal-length sections, and DC sections were randomly assigned as either nonenhanced DC or DC enhanced with 0.15 (Exp. 1), 0.35 (Exp. 1 and 2), or 0.50% (Exp. 2) LAC at a target of either 105 (Exp. 1) or 112% (Exp. 2) of the raw product weight. Enhancement with 0.15 and 0.35% LAC did not (P > 0.05) affect postenhancement pH of DC strip loins when enhanced at a target of 105% (Exp. 1); however, postenhancement pH was reduced (P < 0.05) substantially by LAC enhancement at 115% of raw product weight, with pH values of DC sections enhanced with 0.50% LAC being similar (P > 0.05) to those of CH strip loin sections (Exp. 2). In Exp. 1, raw steaks from CH strip loins had greater (P < 0.05) a* and b* values as well as Japanese beef color scores compared with steaks from nonenhanced and LAC-enhanced DC strip loins across the first 3 d of simulated retail display (LAC enhancement × retail display duration; P < 0.01). Again in Exp. 2, raw steaks from CH sections had greater (P < 0.05) L*, a*, and b* values and Japanese color scores than did steaks from DC sections, regardless of LAC enhancement; however, mean Japanese color scores of CH steaks were only 0.7 and 0.4 units greater (P < 0.05) than the color scores of DC steaks enhanced with 0.35 and 0.50% LAC, respectively. In Exp. 1, CH steaks received the highest (P < 0.05) cooked color and degree of doneness scores, yet scores for CH steaks and steaks from DC sections enhanced with 0.50% LAC did not (P > 0.05) differ when cooked to 71°C in Exp. 2. Fresh and cooked color of DC beef was only minimally altered when enhanced with 0.35% LAC at 105% of the fresh product weight; however, when DC beef was enhanced with 0.35 and 0.50% LAC at a target of 112%, fresh and cooked color were improved close to that of CH beef. Because the persistent red or pink cooked color of DC was virtually eliminated by 0.50% LAC enhancement, LAC-enhanced DC beef may be suitable for food-service markets; however, the raw or fresh color results of Exp. 2 suggested that the fresh color of DC beef can be improved to the color of normal pH beef by postmortem acidification, leading to the possible recoupment of most, if not all, of the lost value associated with DC beef.

Functional stability of frozen normal and high pH beef

The functional properties of whole, diced or minced high and normal pH beef were determined after 0, 1, 2, 3 and 7 month’s storage. There was no interaction between pH, degree of comminution and storage time for most of the attributes measured. Regardless of storage time or comminution method, high pH meat had significantly ( P < 0.001) higher sarcoplasmic protein solubility, water holding capacity, cooked batter torsion stress and strain, yield and emulsion stability than normal pH meat. Normal pH meat had significantly ( P < 0.01) higher myofibrillar protein solubility and hue angle than high pH meat. Water holding capacity significantly ( P < 0.01) decreased and hue angle increased with the increase in the degree of comminution. Protein solubility in raw meat and the cooked batter stress, strain, yield and emulsion stability of both high and normal pH meat deteriorated with time. However, this deterioration was faster in the normal pH meat compared to high pH meat except for total and myofibrillar protein solubility. Within the parameters of the present study, it is concluded that frozen high pH meat possesses superior functional attributes compared to normal pH meat regardless of the degree of comminution or storage time.

Consumer acceptability of dark, firm and dry (DFD) and normal pH beef steaks

The sensory attributes of dark, firm and dry (DFD) and normal pH beef, both raw and fried, were evaluated and compared by a consumer panel ( n=64). Consumer sensory evaluations indicated that the general appearance ( P<0.05), colour ( P<0.001) and acceptability ( P<0.01) of raw normal pH steaks were preferred to those of raw DFD steaks. Twice as many panellists preferred the raw normal pH than raw DFD steaks because of the more attractive red colour, compared to the almost black colour of raw DFD steaks. No significant differences were found between the hedonic ratings of the sensory attributes of fried normal pH and fried DFD steaks. It was expected but not confirmed that consumers would find the tenderness of the DFD steaks more acceptable compared to the normal pH steaks. However, when forced to choose, female consumers significantly preferred fried normal pH steaks to fried DFD steaks, presumably because of a better flavour and more acceptable colour.

Factors influencing resuscitation and growth of heat injured Listeria monocytogenes 13-249 in sous vide cooked beef

The growth of Listeria monocytogenes 13-249 in vacuum-packed, minced beef was investigated as a function of degree of heat injury (including no injury i.e. uncooked beef), growth phase (logarithmic and late stationary phase), pH (5.6 and 6.2), and storage temperature (3, 10 and 20°C) during a storage period of 30 days. Late logarithmic and late stationary phase cultures of L. monocytogenes 13-249 showed similar growth in refrigerated, vacuum-packed, raw minced beef with a high pH (6.2). In normal pH (5.6) beef there was no growth at 3°C while growth at 10 and 20°C was only observed for logarithmic phase cultures. Heat injured late stationary phase cultures with 95–99.9% injured cells in the surviving population (as measured by differential plating on enriched vs. selective media after sous vide cooking) did not grow or repair sublethal injuries in sous vide cooked beef at 3°C while repair and growth took place at 10 as well as at 20°C. In logarithmic phase cultures heat injury occurred very rapidly and ≥99.9% heat injury was observed in all trials in spite of much lower pasteurization values and fewer log 10 reductions compared with late stationary phase cultures. Regardless of growth phase, all cultures where a high degree of heat injury (≥99.9%) was observed, did not subsequently grow in the beef product at 3 or 10°C within 30 days. Growth of heat injured cultures preexposed to heat shock (46°C, 30 min) or slowly rising temperatures (0.3°C min −1) before heat injury was also investigated. Heat shocked or heat adapted cultures generally responded in the same manner as non-stressed cultures (no growth at 3°C) except that a longer lag phase was observed in beef processed at slowly rising temperatures and in normal pH beef at 10°C. Although processing at slowly rising temperatures may slightly increase the survival of L. monocytogenes 13-249 in cooked beef, there seem to be no indication of an increase in subsequent growth potential of the surviving cells.