Research concerning rate and extent of tenderization has focused on beef or lamb. However, it is critical to understand these processes in pork, especially as retailers move towards minimally processed or non-enhanced product. The objectives of this experiment were to evaluate the textural properties of pork (firmness and tenderness) by examining numerous carcass traits and meat quality measurements which may help explain observed differences in pork loin chops. Pigs from 4 proprietary sire lines (A, B, C, D), but common dam line, were raised under similar management practices and slaughtered on the same day at a commercial facility. Pigs (n = 13-16) closest to pen average were selected for each sire and gender, based on live weight. At slaughter, carcass data for each pig was collected. From boneless loins, quality measurements for color, marbling, firmness, instrumental color, pH, drip loss, and proximate analysis (moisture and fat) were measured. Additionally, collagen content (soluble and insoluble), sarcomere length, and western blots (desmin degradation) were examined. Loins were cut into sections and randomly assigned to aging days of 1, 14, 28, or 42 d postmortem. After the respective aging periods, chops were cut from each section and individually vacuum packaged and frozen at -30 degrees C. Chops for Warner-Bratzler shear force (WBSF) were cooked to an internal temperature of 70 degrees C. Cook loss and cooked proximate analysis were measured on the same chop used for WBSF. To investigate rate and extent of tenderization, loins were evaluated on an individual basis and assigned to categories based on the change in WBSF from 1 to 14 d postmortem. Loins which had a change in WBSF of +/-0.3 kg between aging days were characterized as more tender or less tender. Loins that did not change were characterized as no change. The D sire line had less fat depth and greater percent lean than the C line (P less than 0.05). Barrows were fatter than gilts, as evident by more subcutaneous fat, lower percent lean, and more intramuscular fat (P less than 0.05). Pork quality measurements were inconsistent over sire line, indicating no advantage to one specific line. Measurements of collagen were lower (P less than 0.05) in barrows than in gilts. pH was correlated to most of the traits measured (P less than 0.05) and is therefore a useful tool to differentiate products of varying quality. Pork firmness was correlated to a variety of traits (P less than 0.05). Firmness had the strongest relationship to pH (r = 0.44; P less than 0.05). Stepwise prediction equation included pH, L*, and marbling score, but only explained 33% of the variation in firmness. Overall, pork was very tender at 1 d postmortem with a mean shear value of 2.9 kg; however, there was a lot of variation around the mean. Shear force decreased about 20% from 1 to 14 d postmortem (P less than 0.05). Correlations between shear force and the measured quality traits were inconsistent across aging days and the few significant correlations (P less than 0.05) showed a weak relationship (r less than 0.30). Stepwise regression equations did not contain a common set of traits for all aging days. At 1 d postmortem, the prediction equation could explain 25% of the variation in shear force. At 14, 28, and 42 d postmortem, prediction equations could only explain 26%, 17%, and 11% of the variation, respectively. When segregating loins based on change in shear force between 1 and 14 d postmortem, there was not one unique trait that explained the differences in aging rate (P less than 0.05). In the current population of pigs, no single factor or multiple factors were able to adequately or consistently explain differences in firmness or shear force. For the pork industry to move forward with improving quality and consistency, more research needs to address the factors that affect the textural properties of pork. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]