Date of Award
Master of Science
Steven M. Lonergan
Consumers value and are willing to pay for consistently tender and juicy pork products. However, large variations in pork quality exist in the current market place. Predicting pork quality is difficult due to it being a multifactorial issue. To better understand the development of pork quality we performed two studies to analyze the impact of different storage and aging practices as well as variations in the sarcoplasmic proteome between tough and tender pork products. Finding robust and consistent measurements for determining differences in pork quality is essential to identifying variations in pork quality in the current marketplace.
The objective of the first experiment was to observe the aging response of fresh pork loins over 21 days (d) aging, determine the impact of post-aging freezing on pork quality attributes, and document the relationship between two instrumental tenderness (Star probe (SP) and Warner-Bratzler shear force (WBS)) measurements. It was hypothesized that 1) aging to 21 d would impact pork quality features, 2) post-aging freezing would decrease pork quality attributes, and 3) SP and WBS are highly related. Both loins from 20 carcasses were collected one day postmortem from carcasses of Duroc sired crossbred pigs at a commercial harvest facility. Eight loin chops (2.54 cm thick; longissimus muscle) were fabricated from each loin and vacuum packaged. Four chops from each carcass were aged for 1, 8, 14, and 21 d at 4ÃÂ¯ÃÂ¿ÃÂ½ C and evaluated immediately (Fresh). Four chops adjacent to fresh chops were frozen (-29ÃÂ¯ÃÂ¿ÃÂ½ C) post-aging for two weeks, thawed, and evaluated for quality attributes (Frozen). At completion of each treatment (Fresh or Frozen), adjacent pairs of chops were evaluated for purge, Hunter L, a, and b value, pH, color and marbling score, cook loss, and SP or WBS. Desmin degradation was analyzed using whole muscle (myofibrillar and sarcoplasmic) protein extracts from fresh samples at each day of aging. Post-aging freezing had no significant impact on SP, WBS, pH, color score, marbling score, or Hunter L value at any aging period (P>0.05). Fresh chop purge increased at each d of aging (P<0.01). Greater purge at 1, 8, and 14 d aging resulted from post-aging freezing (P<0.01). Post-aging freezing chop purge was not different at 21 d aging compared with 8 d aging (P>0.05). Less cook loss was observed in post-aging freezing chops after 1 d aging (P<0.01) but was not different after 8 d aging when compared with 14 and 21 d (P>0.05). Post-aging freezing chop cook loss was less than fresh chop cook loss at 14 and 21 d aging (P<0.05). Chop Hunter L value increased (P<0.01) from 1 to 8 and 14 to 21 d aging regardless of treatment. Chop Hunter L value was not different at 8 and 14 d aging regardless of treatment (P>0.05). Chop a value was less (P<0.01) at 1 d aging than any other aging period in each treatments. Post-aging freezing resulted in greater chop a value at 1 d aging (P<0.01). Star probe value was correlated (r= 0.85; P<0.01) with WBS values across all aging timepoints and treatments. Intact desmin in whole muscle protein extracts decreased (P<0.01) between 1, 8, and 14 (1.17, 0.64, and 0.50 respectively) d aging but was not different from 14 to 21 d aging (0.50 and 0.52, respectively, P>0.05). The results demonstrate aging did not improve SP or WBS values after 8 d aging. This result is similar to the observed changes in desmin degradation. Instrumental tenderness measurements of SP and WBS are highly correlated. Post-aging freezing did not impact color, marbling, Hunter L, or instrumental tenderness. Freezing pork prior to aging will not allow significant improvement in SP or WBS values.
Experiment 2 used a subset of samples from experiment 1 to analyze the sarcoplasmic proteome between experimental groups differing extremely in SP value at 21 d aging. The objectives of this study were to determine the extent to which the sarcoplasmic proteome at 1 d postmortem can explain variations in aged pork quality. Twelve pork loins were categorized by differences in Star Probe (SP) (kg) measurements at 21 d postmortem. Pork loin quality attributes (purge, color, marbling score, SP and cook loss) were measured at 1, 8, 14, and 21 d postmortem. Whole muscle (myofibrillar and sarcoplasmic protein extract) desmin degradation and sarcoplasmic calpain-1 autolysis was determined using SDS-PAGE and Western blot techniques. Loins were sorted into two libraries of samples: Low SP group (LSP) (n=6) (SP<5.80 kg at 21 d postmortem), and High SP group (HSP) (n=6), (SP>7.00 kg at 21 d postmortem). Inclusion parameters of marbling score (1.0-3.0) and pH value (5.69-5.98) were set. Two-dimensional difference in gel electrophoresis (2D-DIGE) and mass spectrometry were used to determine sarcoplasmic proteome differences between experimental groups. The LSP group had a lower (P<0.01) SP value at each d of aging compared with the HSP group. Chop purge was lower (P<0.01) in the LSP group at 14 and 21 d aging but did not differ at 1 and 8 d aging (P>0.05) compared with the HSP group. The LSP group had a greater pH at each d of aging (P<0.05) compared with the HSP group. Marbling score was also greater in the LSP group compared with the HSP group at each d of aging (P<0.05). Cook loss was lower in the LSP group compared with the HSP group at 8 and 21 d aging (P<0.05) but did not differ between categories at 1 and 14 d aging (P>0.05). Desmin degradation was greater in the LSP chops compared with the HSP chops at 14 and 21 d aging (P<0.05). Color score, Hunter L, a, b, and calpain-1 autolysis were not different between SP groups. Identified protein spots from 2D-DIGE determined that star probe groups had differing abundance of metabolic, mitochondrial associated and regulatory proteins in the sarcoplasmic fraction. The LSP had greater abundance of stress response proteins. Differences in pork quality and proteolysis were observed between experimental groups. Glycolytic, regulatory, and stress response proteins may be used as potential biomarkers at 1 d postmortem to predict aged pork loin quality differences. The results identify that not only proteolysis is important in the development of pork tenderness but also other protein changes, specifically in the sarcoplasmic fraction, have impacts on tenderness development. Further identification of the role of these biomarkers will assist with understanding the development of pork tenderness.
Matthew David Schulte
Schulte, Matthew David, "The impact of aging time, storage type and early postmortem sarcoplasmic proteome variations on pork loin quality" (2018). Graduate Theses and Dissertations. 16875.