Characterization of loin shape from Duroc and Duroc composite finishing gilts.

Gilts (n=45) were used in this study to characterize the effect of genotype on loin characteristics and quality over the length of the loin. Three diverse genotypes included a high quality Duroc line (A), a Duroc based composite line selected for lean growth (B), and an F1 cross of the two (C). After harvest, bone-in loins were removed from the carcass and cut perpendicular to the backbone at the 5th/6th rib, 7th/8th rib, 10th/11th rib, last rib, midlumbar, and the loin/sirloin juncture. Quality measurements were obtained at the 5th/6th rib, 10th/11th rib, and the loin/sirloin juncture. Digital images were taken of each surface (n=6) and analyzed for the determination of loin muscle area (LMA), muscle width, muscle depth (at three locations across the loin face), and fat depth. The average loin depth was calculated and used to calculate the loin depth:width ratio as an indication of loin shape or conformation. Loins from line A had the lowest (P<0.05) subjective color score, had the highest (P<0.05) amount of marbling, and were the firmest (P<0.05) of all three lines. There were also differences (P<0.05) between genetic lines for LMA, width, all three depths, fat depth, and depth:depth ratios. The most posterior portions of the loin had the largest (P<0.05) LMA, loin width, fat depth, and muscle depth 1. However, the more anterior portions of the loin had greater (P<0.01) values for the depth:width ratio and muscle depth:depth ratios.

The effect of pH on shelf-life of pork during aging and simulated retail display.

The pork industry uses pH to differentiate product of varying quality; thus, the effect of pH on shelf-life is important as time during transport is extended. The objective was to develop regression equations to predict shelf-life over a range of ultimate pH (5.42-6.26). Shelf-life was evaluated after vacuum aging pork loin sections 0, 7, 14, 21, or 28d and during 3d of simulated retail display (4.5°C) for pork loin chops. Correlation coefficients indicated a strong relationship between pH and quality measurements. Regression analysis with Aging Day and pH was able to explain 87% of the variation in aerobic plate counts for pork. After 28d of vacuum aging, loin sections from the upper end of the pH distribution had about a 3log(1000X) greater aerobic plate count than did the lower end pH product. An increase in pH resulted in pork with lower L*, a*, b* and R(630)-R(580) values and as Aging Day increased, instrumental measurements of color increased slightly. Although higher pH is associated with improved pork quality, higher pH and longer aging periods will result in increased microbial proliferation and decreased shelf-life. Thus, an intermediate pH may provide the most desirable combination of quality and shelf-life when extensive aging is used.

Effect of level, source, and time of feeding prior to slaughter of supplementary dietary magnesium on pork quality.

A total of 192 pigs were utilized in a 2×3×3 factorial arrangement with an additional control treatment. The treatments were: (1) magnesium level (1.6 vs. 3.2 g of magnesium pig(-1) day(-1)); (2) magnesium source (sulfate vs. proprionate vs. proteinate); (3) feeding duration (5 vs. 2 vs. 1 day), and a control (no supplementary magnesium). Minolta L(∗) values were lower (P⩽0.05), indicating darker muscle color, for pigs supplemented with 1.6 g magnesium pig(-1) day(-1) compared to the controls while pigs on the 3.2 g magnesium level were intermediate between these two treatments. Animals on the 1 day treatment had a higher (P⩽0.05) ultimate pH and lower (P⩽0.05) Minolta L(∗) compared to those on the 2 days and control treatments, while 5 days pigs were intermediate and had lower L(∗) values compared to the controls. The sulfate and proteinate treatments produced pork with the lower (P⩽0.05) Minolta L(∗) values compared to the controls. Pigs fed the sulfate diet had a lower (P⩽0.05) drip loss compared to those on the control treatment. Results from this study suggest that the lowest level (1.6 g magnesium pig(-1) day(-1)) and the shortest time of supplementation (1 day) may be effective in improving pork color and water-holding capacity.

Myosin heavy chain isoforms account for variation in pork quality.

The objective of this study was to determine the impact of myosin heavy chain (MyHC) isoforms (I, IIB, IIA and IIX) on pork quality traits of halothane (HAL)-negative (NN) and halothane-carrier (Nn) pigs. Gilts (n=32) were assigned to a 2×2 factorial of genetic population (GP) and slaughter weight (WT; 120 and 135 kg). Classical meat quality characteristics were collected and MyHC content was determined on muscle samples. Regression equations for pork quality and carcass composition traits were determined. Only I/IIB accounted for variation in drip loss of NN gilts (R(2)=0.18), while GP related to drip loss in Nn gilts (R(2)=0.70). Type I MyHC content explained variation in ultimate (24 h) muscle pH of NN gilts (R(2)=0.09), while I/IIB, I/IIX and IIB/IIX were significant for Nn gilts (R(2)=0.99). I/IIA, I/IIX, IIB/IIX and GP accounted for variation in Hunter Color a (redness) values of NN gilts (R(2)=0.69), while IIB, IIA, IIB/IIA and GP were significant for Nn gilts (R(2)=0.97). Overall, fiber type composition accounts for a larger proportion of variation in the quality traits of Nn compared to NN gilts.

Effects of conjugated linoleic acid on the belly firmness and fatty acid composition of genetically lean pigs.

A study of the effects of conjugated linoleic acid (CLA) on the belly firmness and fatty acid composition of genetically lean pigs was conducted. From 75 to 120 kg live weight, 30 gilts were allowed ad libitum access to a corn-soybean meal diet supplemented with either 1% CLA oil (CLA-60) or 1% sunflower oil (SFO) or were fed the sunflower oil-supplemented diet restricted to the amount consumed by pigs fed the CLA-60 diet (RSFO). Conjugated linoleic acid oil consists of 60% positional and geometric isomers of CLA. Pigs fed SFO exhibited higher average daily gains (0.98 vs 0.80 kg/d, P < 0.01) than RSFO-fed pigs, but there were no effects of dietary treatment on feed intake or feed efficiency. Dietary treatment did not affect (P > 0.05) backfat thickness or longissimus muscle area. Bellies of gilts fed CLA-60 were subjectively evaluated to be firmer (2.91 vs 2.43 or 2.07 +/- 0.13, P < 0.01) than those of SFO- or RSFO-fed gilts, respectively. The longissimus muscle of gilts fed CLA-60 contained more saturated fatty acids (39.77 vs. 36.04 or 36.73 +/- 0.74%, P < 0.001) and less unsaturated fatty acids (60.23 vs 63.96 or 63.27 +/- 0.74%, P < 0.001) than that of gilts fed SFO or RSFO, respectively. The belly fat of gilts fed CLA-60 contained more saturated fatty acids (44.45 vs. 37.50 or 36.60 +/- 0.46%, P < 0.001) and less unsaturated fatty acids (54.78 vs. 61.75 or 62.47 +/- 0.46%, P < 0.001), resulting in lower iodine values (57.69 vs 66.37 or 65.62 +/- 0.91, P < 0.001) than that of gilts fed SFO or RSFO, respectively. Gilts fed CLA-60 accumulated more CLA in the longissimus muscle (0.55 vs 0.09 or 0.09 +/- 0.03%, P < 0.01) and belly fat (1.56 vs. 0.13 or 0.13 +/- 0.15%, P < 0.001) than did gilts fed SFO or RSFO, respectively. Dietary treatment did not affect (P > 0.05) 24-h pH, drip loss or subjective quality evaluations of the longissimus muscle. The effect of supplemental CLA to improve belly firmness is of practical significance and may provide a nutritional solution to carcass fat and belly firmness problems, thereby enhancing the overall value of extremely lean carcasses.