Investigating Meat Quality of Broiler Chickens Fed on Heat Processed Diets Containing Corn Distillers Dried Grains with Solubles

The protocol for the present experiment was approved by the Institutional Animal Care and Use Committee of Kangwon National University, Korea. This experiment was designed to evaluate the interaction of feed processing and DDGS on the growth performance of broilers. A total of 720 broilers (Ross 308; average BW [body weight] 541±5.7 g) were randomly assigned based on BW and sex to 6 dietary treatments. A randomized complete block design with a 3×2 factorial arrangement of treatments Isocaloric and isonitrogenous diets were used to investigate the response of broiler chickens to two levels of DDGS (0 and 200 g/kg diet), in mash, simple pellet (SP) and expanded pellet (EP) forms. Each treatment had 6 replicate pens with 20 broilers (10 males and 10 females) per pen. Prior to the experiment, the birds were fed a standard broiler starter diet and management from d 1 to 14.

The mash diet was formulated to contain 3,150 kcal kg^–1 of ME, 210.0 (g/kg diet) CP, and 11.0 (g/kg diet) total lysine; supplemented with vitamins, minerals and AA to meet or exceed the nutrient requirements listed in Ross 308 nutrition specification (Aviagen, 2014). For the SP diet, the mash diet was steam conditioned to 75°C and pelleted using a 220 hp pellet mill (Model M12, Matador, Denmark) with a 2.8 mm die in diameter. The EP was produced by subjecting the mash diet to a 300 hp expander (Model M12, Matador, Denmark) with 180 amperes, a gap opening of 39% and temperature of 105°C. The expanded diet was further processed through a pellet mill similar to the one used for the SP diet. The experiment duration was 21 d, and the final BW was approximately 2.02 kg.

The birds were housed in rice hull-covered floor pens. Each pen was provided with a self-feeder and hanging bell drinker to allow free access to feed and water. The house temperature was 23°C and lighting was provided for 23 h/d.

At the end of experiments, 72 birds (2 birds per replicate) were randomly selected and slaughtered by cervical dislocation. The whole slaughtering process was in the local slaughter floor of the laboratory, to avoid birds suffering from stress due to long transport time, according to the specifications outlined in the Korean legislation. After bleeding for 2 min, birds were scalded in water at 60°C for 2 min before feather plucking by a machine, evisceration, and tissue sample collection.

The fatty acids profile was measured using the previously reported methods by Kim et al. (2014). In brief, all layers of adipose tissue from the left side thigh were utilized for fatty acids determination. Total lipid was extracted from the adipose tissue samples with a chloroform and methanol (2:1, v:v) mixture and quantified gravimetrically. Fatty acids in each lipid were derivatized to methyl esters according to Lepage and Roy (1986). Separation of fatty acid methyl esters was achieved by gas chromatography (GC-17A, Shimadzu, Japan) equipped with 100 m fused-silica capillary column with i.d. of 0.25 mm, a 0.20 m film coating and SP™-2560 column stationary phase (Sigma-Aldrich Co. LLC, USA), and flame ionization detector. Helium (purity 99.99%) carrier gas was employed as a carrier gas at a constant column flow of 1.0 mL/min. Oven temperature was maintained at 175°C for 30 min, increased at 5°C per min to 215°C, and then increased at 10°C per min to 235°C. Injector and detector temperature was maintained at 260°C. Methyl ester standards were used to identify sample fatty acid methyl esters.

Drip loss was measured using approximately 2 g of meat sample according to the plastic bag method described by Honikel (1998) Cook loss was determined as described previously by Sullivan et al. (2007). Briefly, 5 g of breast meat were heat-treated in plastic bags separately in a water bath (100°C) for 5 min. Samples were cooled at room temperature. Cooking loss was calculated as (sample weight before cooking – sample weight after cooking)/sample weight before cooking×100. The pH value was determined using pH meter (IstekNeoMet 77P, Istek Inc, Korea). The shear force was measured using a texture analyzer (TA-XT2i, Stable Microsystems Ltd., UK) equipped with a 25 kg load cell, a Warner-Bratzler shear blade, and a test speed setting at 2.0 mm/s. Only the maximum force (kg) was taken into account.

After slaughter, carcass traits like pectoralis muscle, supracoracoideus, total breast, breast skin, abdominal fat, thigh, drum, wing and back measured. They are expressed as percent of the live weight. Breast meat was also collected and the meat color values were measured freshly. The breast meat was allowed to air-dry for 30 min and Minolta color values were measured for lightness (L*), redness (a*) and yellowness (b*).

Data generated in this experiment was analyzed as a 3×2 factorial arrangement in a completely randomized design. Pen was the experimental unit for statistical analysis. Broiler chickens were experimental units for measuring the fatty acids profile, meat portions, meat quality. The main effects of feed processing and DDGS, and their interaction were determined by mixed procedure of SAS statistical program (SAS Inst., Inc., USA). P-values≤0.05 were considered statistically significant.

The data for meat quality parameters are presented in Table 1, which indicate that meat drip loss and cooking loss were not affected by the DDGS level or processed feed. Our results indicated that drip loss was not significantly influenced by dietary DDGS or feed processing. These results are consistent with the reports of previous studies (Corzo et al., 2009; Jiang et al., 2014), which showed that DDGS supplementation in broiler diet did not negatively affect drip loss and cooking loss. However, the addition of 25% DDGS in broiler diet significantly decreased cooking loss (Min et al., 2009). Administration of DDGS and EP diet significantly increased (p<0.01) the shear force of breast meat, which is consistent with the report Schilling et al. (2010). Jiang et al. (2014) reported that higher level of DDGS in broiler diet increased the shear force of breast meat. Therefore, higher dietary DDGS levels led to poor meat tenderness. However, the shear force was <30 N in all samples, indicating that it would still be acceptable to consumers (Corzo et al., 2009; Schilling et al., 2010). Our result showed that broilers fed EP diet showed increased shear force. The relationship between muscle shear force and processed feed has not been concretely established yet. There was an interaction between feed processing and DDGS level with meat lightness (L*), indicating a lighter breast meat color. However, Jiang et al. (2014) found that dietary DDGS had no effect on meat color. Conversely, our results indicated that meat color was significantly influenced by processed feed.

The effect of DDGS content and processed feed on fatty acids profile of the thigh is presented in Table 2. On adding DDGS to the diet, C18:0 and C22:0 were both significantly decreased (p<0.05). SP and EP diets increased the content of C16:0 in thigh meat, but decreased the ratio of linolenic acid (p<0.05). Previous researches have demonstrated that the impact of 15% DDGS in the diet on fatty acids digestibility significantly increased polyunsaturated fatty acids and decreased that of short-chain fatty acids, and medium-chain fatty acids in the thigh meat of broiler chickens (Jiang et al., 2014); however, little is known about the effects of DDGS in expanded diet on the fatty acids profile of the thigh. The percentage of linolenic acid in the thigh decreased in EP diet-fed chickens. High-temperature conditions during feed processing can increase the hydrolysis of fatty acids; in particular, free fatty acids and polar lipids with double bonds have a higher potential for reacting under these conditions (Tran et al., 2008). Linolenic acid is a nutritious essential fatty acids with three double bonds, which makes it more vulnerable in high temperatures. The pelleting process may decrease linolenic acid in the diet, consequently leading to a lower linolenic acid percentage in the thigh.

Variable responses to meat portions were observed at the end of experiment (Table 3). No interactions (p>0.05) between the FP and DDGS were detected for meat portions, but significant differences were observed in main effects (p<0.05) of FP. The addition of DDGS did not change any of meat portions. Feed processing increased the percentage of pectoralis muscle and drum but tended to decrease supracoracoideus muscle ratio compared with chickens fed mash-fed chickens (p<0.05). EP-fed chickens were found to have a higher ratio of back mass than mash-diet fed chickens (p<0.05). The higher portion for pectoralis muscle, drum, and back mass in chickens fed pelleted diets in the current study is in line with the result of Bricket et al. (2007). The current study showed that breast muscle yield tended to decrease in high DDGS treatment. The effects of various contents (%w/w) of DDGS on processing parameters on 49 d showed that breast muscle yield significantly decreased with increasing DDGS levels from 0% to 50% in a concentration-dependent manner (Wang et al., 2008). However, Shim et al. (2011) reported that processing measurement results were similar for chickens regardless of the DDGS content, and the only significant difference among treatments was in carcass measurements, where the percentage of fat in the female carcasses increased with increasing DDGS content in the diet.