Establishing the relationships among carcass characteristics and meat quality traits of pork

Barrows and gilts (N=1238) with the same genetic background, housing, and management were raised under commercial conditions and marketed when the average pig weight in a pen reached 138 kg. Pigs were slaughtered over 7 weeks in a commercial processing facility. Carcass length was measured on the left side of each carcass from the anterior of the aitch bone to the anterior of the first rib at 1-d postmortem. Carcasses were fabricated and boneless Canadian back loins (IMPS #414) were vacuum-packaged and transported to the University of Illinois Meat Science Laboratory. At the end of the 14-d aging period, loins were weighed, measured for stretched length (stretched to maximum length without distortion), compressed length (compressed to minimum length without distortion) and sliced into 2.54cm chops using a Treif Puma slicer. Complete boneless chops were counted and ends and incomplete chops were weighed. From the initial population, 286 boneless loins (NAMP #414) were further selected based on instrumental L* color and extractable lipid content resulting in a 5 x 6 factorial arrangement of treatments. Using these values, chops were also assigned a quality grade using the newly developed National Pork Board (NPB) quality grade standards. Low (n = 33) quality includes loins with color scores < 2.5 and marbling scores ≤ 2.0. Medium (n = 203) quality includes color scores 2.0 through 3.5 with marbling ≥ 2.5, color scores from 3.0-3.5 with marbling scores ≥ 1.5, and color scores ≥ 4.0 with marbling scores < 1.5. High (n = 50) quality includes color scores of > 4.0 with marbling scores ≥ 2.0. Chops were assigned to sensory panel sessions in an incomplete block arrangement, cooked to a medium-rare degree-of-doneness (63 °C) and evaluated for tenderness, juiciness, and pork flavor by trained sensory panelists. Slice shear force (SSF) and cooking loss were also determined from each loin cooked to 63 °C. 
\nData were analyzed using the REG procedure in SAS and the effect of NPB quality grade was analyzed using the MIXED procedure in SAS as a one-way ANOVA where quality grade was considered a fixed effect. Carcass length varied from a minimum of 78.2 cm to a maximum of 96.5 cm. Boneless loin yield varied from a minimum of 13 chops to a maximum of 20 chops. Carcass length explained 15% (P < 0.0001) of the variation in boneless loin chop yield. Loin weight explained 33% (P < 0.0001) of the variation in boneless loin chop yield. Compressed loin length explained 28% (P < 0.0001) of the variation in boneless loin chop yield. Stretched loin length explained only 9% (P < 0.0001) of the variation in boneless loin chop yield. The combination of loin weight and compressed loin length was able to explain 39.3% (P < 0.0001; C(p) = 12.399) of the variation in boneless loin chop yield using a required F statistic at the SLENTRY and SLSTAY level = 0.15. Instrumental L* color score ranged from 43.11 to 57.60 and extractable lipid ranged from 0.80% to 5.52%. Extractable lipid content and instrumental chop color individually accounted for a maximum of 2% (R2 = 0.02) of the variation of tenderness, juiciness or pork flavor. Chops categorized as NPB high quality (SSF = 17.50 kg) were 6.5% more tender (P≤ 0.02) than chops categorized as medium (SSF = 18.68 kg) and 11.2% more tender then chops categorized as low quality (SSF = 19.59 kg), but medium and low quality chops did not differ in SSF. However, trained sensory panelists did not discern tenderness differences (P = 0.13) among NPB quality grades. Juiciness (P = 0.43) and flavor (P = 0.11) scores did not differ among NPB quality grades. Cook loss tended (P = 0.06) to decrease from 16.86% to 15.32% as quality grade increased.
\nOverall, carcass length is a poor predictor of boneless loin chop yield. However, using boneless loin parameters such as boneless loin weight and compressed loin length may be more predictive of the number of chops produced from a boneless pork loin. Further, when color or marbling was used as a single trait, it was not predictive of sensory quality. However, using these traits in combination such as with the NPB quality grades may result in differences in sensory quality between pork loins.

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