Exploring prediction of pork mid-loin marbling from the Latissimus dorsi

With Canadian pork carcass cutting lines, the latissimus dorsi (LatD; large deckle), which exhibits a wide range of marbling, is exposed on both the primal loin and the primal belly. The relationship between LatD marbling and marbling at the grading site of the longissimus dorsi (LD) was explored with the view to predicting the latter from the former for the purpose of early on-line sorting. Monochrome images of the LatD were captured to create a 5-step subjective marbling scale which was used to assess the LatD in 1,385 library images of the cut surface of the belly. Of the loin grade sites corresponding to these bellies, 638 had data for subjective marbling scores (NPPC), 1,140 had percent intramuscular fat (%IMF), and 393 had both.

The available dataset showed a skewed marbling distribution: 75% of the group of 393 loins had ≤ 2.5% IMF, 68% of the group of 1,140 loins had ≤ 2.5% IMF, and 81% of the group of 638 loins had NPPC scores ≤ 2. Within the loin, the %IMF correlation with NPPC was r = 0.81 (P < 0.0001). Correlations of subjective LatD score with %IMF or NPPC were r = 0.57 and 0.48 (P < 0.0001) respectively. Conversion of %IMF to 6 categories of 1% each showed the lowest category (0.5-1.5%) was best represented by LatD marbling score 2, while the highest LatD marbling score of 5 was equally present in the 4 highest %IMF categories (2.6-5.6+%). Taking into consideration the sub-optimal population distribution and coarse features of the LatD in library images, correlations were thought promising. Planned future work will include assessment directly on fresh meat, analysis of high resolution LatD images, and grade site %IMF and marbling score for every loin.