An important topic of discussion in the pork industry today is the fat quality of pork carcasses. It is well known that low quality fat (soft, oily fat) can have negative effects on the quality attributes of both fresh and processed meat products. For instance, soft fat can cause decreased shelf-life due to greater susceptibility for fat rancidity, greater occurrences of off-flavors, unattractive fat smearing in further processed products like sausage, and less apparent slice definition for sliced, packaged bacon. The primary factors currently being studied that affect pork quality are of dietary origins. With the current high demand for bio-fuels there is an abundant availability of co-products such as dried distillers grains with olubles’ (DDGS). In fact, since 2001 the estimated use of DDGS in swine diets has drastically increased to about 3 million metric tons. Due to their abundance and reasonable price the use of DDGS in the swine diet can result in substantial savings in feed costs. However, DDGS contain high levels of unsaturated fats that could result in softer pork carcass fat when fed at high enough levels. In order to improve or maintain the quality of pork fat, researchers have begun to experiment with other ingredients in the swine diet. Glycerol, another bio-fuel co-product, has become a research topic to improve pork fat quality. Glycerol has been reported to increase the saturation of pork back fat. Therefore, the goals of this study were to determine the impact of 0 and 20% DDGS and the inclusion of glycerol at levels of 0, 2.5, and 5% in grow-finishing rations on loin and bacon quality, and determine the relationship between belly firmness and slicing yield for commercially produced bacon.

This study was conducted in a commercial swine facility with pigs being fed corn-soybean based diets. 70 days prior to slaughter, 1,160 pigs were randomly assigned to 1 of 6 dietary treatments consisting of 0% DDGS in combination with 0, 2.5, or 5% glycerol or 20% DDGS with 0, 2.5 or 5% glycerol. On day 70, two barrows from each pen were harvested at a commercial harvest facility. After chilling, loins and bellies were removed from the carcass and transported to the Kansas State University Meat Laboratory for evaluation.

Loins were evaluated for purge loss and then fabricated into pork loin chops. Loin chops were analyzed for drip loss, pH, instrumental color, visual color score, marbling score, Warner-Bratzler shear force (WBSF), fatty acid profile, cooking loss, and trained sensory evaluation.

Belly measurements were recorded for thickness, length and belly weight. Belly firmness was measured using what is called a belly bend or “flop” test. In this test a belly is centered across a bar and the length between the two ends is measured. A smaller length indicates that a belly would be softer (or that it would bend to a greater extent).

Bacon was manufactured by first injecting the raw (green) bellies to 12% of their green weight. While processing, green weight, injected weight, and pump% were recorded. After injection, bellies were cooked in a smokehouse to an endpoint temperature of 53oC and subsequently stored at 2oC for 24 hours. After chilling, cooked bellies were weighed and the smokehouse yield was calculated. Bellies were then transported to a commercial bacon manufacturing facility for pressing, slicing, and packaging. After processing, bacon slice yield was calculated, and samples were collected for proximate analysis (% moisture, protein, fat and ash), fatty acid analysis, and sensory evaluation. During sensory evaluation, bacon slices were evaluated for bacon flavor intensity, brittleness, saltiness, off flavors, and cooking yield.

The addition of glycerol and DDGS to the diet did not appreciably affect any pork loin quality traits with the exception of a minor increase in off-flavor production for the 20% DDGS treatment. This was to be expected as the 20% DDGS treatment also showed an increase in the amount of unsaturation in the intramuscular fat as evidenced by higher calculated iodine values. Feeding glycerol did not affect the saturation level of any of the fatty acids that were tested. However, pigs fed 20% DDGS had higher levels of linoleic acid, eicosadienoic acid, and iodine value indicating that the fat became more unsaturated compared with pigs fed 0% DDGS.

Glycerol and DDGS in combination did not influence belly length, belly thickness, belly firmness, initial weight, green weight, pump percentage, injection weight, cooked weight, smokehouse yield, bacon yield or cooking yield. Feeding DDGS at 20% did not affect belly length, belly thickness, initial weight, or green weight but decreased belly firmness as measured by the belly bend (flop) test. Additionally, 20% DDGS tended to increase pump percentage but did not affect smokehouse yields, slice yield, or bacon cooking yields. Increasing dietary glycerol by 2.5 and 5% tended to increase belly length, but did not affect thickness, belly firmness, initial weight, green weight, injected weight, smokehouse yields, slice yields, or bacon cooking yields. Feeding DDGS at 20% in combination with glycerol or 20% DDGS and glycerol singularly did not affect the proximate composition of bacon slices. Additionally, DDGS and glycerol fed together did not affect fatty acid content. The inclusion of 20% DDGS into diets did not affect the total saturated fatty acid content but increased total monounsaturated and trans-fatty acid content as well as increased unsaturated: saturated and poly-unsaturated: saturated fatty acid ratios, as well as increased iodine values. The inclusion of 2.5 and 5% glycerol showed no effect on fatty acid content. After sensory panel evaluations it was found that DDGS and glycerol together or singularly had no effect on bacon brittleness, bacon flavor intensity, saltiness, or off-flavor development.

Additionally, our results suggest that thicker bellies are correlated with greater smoke house yields, greater slice yields, and firmer bellies. Also, bellies that had larger (firmer) flop skin down scores showed greater smokehouse yields and slice yields.

In summary, feeding DDGS and glycerol in combination or singularly at the levels tested did not practically impact loin quality traits. Feeding 20% DDGS did decrease belly firmness, although, not to a degree that would affect any processing characteristics. Furthermore, our results suggest that the addition of 20% DDGS to finishing swine diets will not be detrimental to sensory components in bacon. Feeding glycerol at 2.5 and 5% of the diet did not positively or negatively affect any fresh belly or bacon characteristic that would increase or decrease the profitability of bacon production. Finally, adding glycerol to the diet 2.5 and 5.0% did not change fatty acid composition of loin intramuscular fat or belly fat.

For more information about the project please contact Terry A. Houser Ph.D., Assistant Professor of Meat Science in the Department of Animal Sciences and Industry at Kansas State University, Phone: 785-532-1253"", E-mail: [email protected]