University of Illinois Urbana-Champaign

Characterization of color stability in the longissimus dorsi, triceps brachii, and psoas major from fresh pork

Barkley, Kayla E.

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BARKLEY-DISSERTATION-2022.pdf

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https://hdl.handle.net/2142/116141

Description

Title
Characterization of color stability in the longissimus dorsi, triceps brachii, and psoas major from fresh pork
Author(s)
Barkley, Kayla E.
Issue Date
2022-05-20
Director of Research (if dissertation) or Advisor (if thesis)
Dilger, Anna C
Doctoral Committee Chair(s)
Dilger, Anna C
Committee Member(s)
  • Harsh, Bailey N
  • Boler, Dustin D
  • Suman, Surendranath P
Department of Study
Animal Sciences
Discipline
Animal Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Pork, Color
Abstract
Consumers discriminate against meat that appears brown in color, perceiving it to be spoiled or not fresh. While color stability in beef is well understood, differences in color stability among and within, muscles have received limited attention in pork. Therefore, the overall objectives of this work were to characterize quality and color stability of pork loin chops that were categorized as stable or labile, and to determine differences in color and biochemical characteristics among the longissimus dorsi (LD), triceps brachii (TB), and psoas major (PM) muscles of pork during simulated retail display. Three total experiments were conducted for this work. For the first experiment, boneless pork loins (N=484) were evaluated for quality traits at 11 or 14 d postmortem. One chop was cut from each loin near the 10th rib for retail display, overwrapped, and displayed under constant fluorescent lighting for 7 d. Objective color, myoglobin (Mb) forms, and subjective visual discoloration traits were evaluated daily. After display, loins were categorized based on final visual discoloration (d7) as: Very Color Stable (VCS; 0 – 5% discoloration), Color Stable (CS; 5 – 10% discoloration), Neutral (NT; 10 – 25% discoloration), Color Labile (CL; 25 – 30% discoloration), or Very Color Labile (VCL; >30% discoloration). Quality and color traits were analyzed using the GLIMMIX (visual discoloration) or MIXED (all other measures) procedure of SAS. Retail display data were analyzed as repeated measures. Loins classified as CS or VCS were darker, less yellow, had greater pH values, greater marbling scores, decreased color score, and decreased purge loss compared to CL and VCL loins (P < 0.01); N loins were intermediate for each of these measurements (P < 0.01). No differences in aged redness were observed between groups (P ≥ 0.16). A group x day interaction was observed for all traits measured during retail display (P < 0.0001). Stable loins generally had increased redness and R630/580 as well as decreased visual discoloration scores, lightness, yellowness, and % MMb values during display. For the second and third experiments, the LD, TB, and PM from the left sides of 20 pigs were used in this study. Muscles were aged in vacuum packages for 21 d, then fabricated to yield 3 chops per muscle. The pH of the most anterior chop from each muscle was measured. All chops from a single muscle were overwrapped and displayed for 5 d under constant lighting. On each display day, packages were evaluated for instrumental color, myoglobin forms and subjective visual discoloration. Chops were removed on d1, 3, or 5, to measure oxygen consumption (OC), metmyoglobin reducing activity (MRA), and lipid oxidation. Day 1 chops were also evaluated for myoglobin content. Data were analyzed using the MIXED procedure of SAS as a repeated measures. Pearson correlation coefficients for changes in measurements between the LD and other muscles were determined using the CORR procedure. Pearson correlation coefficients between initial and final traits were calculated for each muscle using the CORR procedure of SAS. Correlations were compared between the LD, TB, and PM using a Fisher’s z test. Stepwise regression models for prediction of final visual discoloration or 630/580 nm ratio for each muscle were developed using the REG procedure. Over the 5d display period, TB and PM chops had greater changes in a*, b*, chroma, 630/580 nm ratio, DMb, and OMb compared to LD chops (display time x muscle interaction P ≤ 0.01), but the TB and PM did not differ from each other (P ≥ 0.07). Conversely, the LD had decreased OC and increased MRA on each display day compared to the TB and PM (P < 0.01). However, no differences in rate of MMb accumulation during display were observed between muscles (P = 0.10). Using 20% discolored as a threshold for acceptability, 85% of LD samples were considered acceptable while only 5% and 20 % of TB and PM samples were considered acceptable, respectively, on d5 of display. Myoglobin content and pH differed between muscles (P < 0.0001). The LD was correlated with the TB and PM for changes in redness (0.51 ≤ r ≤ 0.55; P ≤ 0.02), and trending towards a correlation or correlated with changes in TB and PM 630/580 nm ratio and hue angle (0.39 ≤ r ≤ 0.63). All initial traits were correlated to final visual discoloration and 630/580 nm ratio in the TB and PM (|0.47| ≤ r ≤ |0.72|), except redness, d1 630/580 nm ratio, OC, and Mb content (P ≥ 0.07). Initial redness and OC were also correlated to final 630/580 nm ratio (|0.45| ≤ r ≤ |0.65|), Final LD discoloration was correlated to initial LD L*, but not any other trait (P ≥ 0.06). Final LD 630/580 nm ratio was correlated to initial L*, a*, hue angle, DMb, and pH (|0.48| ≤ r ≤ |0.75|), but not any other traits (P ≥ 0.06). Yellowness explained the majority of variation in visual discoloration for the TB and PM and instrumental 630/580 nm ratio for all muscles (0.32 ≤ partial R2 ≤ 0.85). Initial lightness (partial R2 = 0.21) and Mb (partial R2 = 0.20) were most predictive of final LD visual discoloration (partial R2 = 0.33). Overall, loins classified as color stable were generally darker, redder, and had greater pH and marbling levels at 14 d postmortem compared to color labile loins. Chops from the TB and PM were less color stable during a 5d display period compared to LD chops, but had few color stability differences from each other. Furthermore, correlations were generally stronger in the TB and PM compared to the LD, but did not differ from each other. In all muscles, meat with improved color stability was initially darker, less yellow, and had lesser hue angles and greater chroma values.
Graduation Semester
2022-08
Type of Resource
Thesis
Handle URL
https://hdl.handle.net/2142/116141
Copyright and License Information
Copyright 2022 Kayla Barkley

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