Birds and husbandry
The experimental protocol was conducted in accordance with the practices outlined in the Guide for the Care and Use of Agricultural Animals in Agriculture Research and Teaching of Northeast Agricultural University (Protocol number: NEAU-[2011]-9).
A total of 600 1-day-male duck (Anas Platyrhynchos) with no significant different weight were purchased from a commercial hatchery and randomly assigned to 4 groups (Table 1), with 10 replicate pens (cages) per group and 15 ducks per pen for a 70-day feeding trial. The basal diets for the three stages (days 1–28, days 29–56 and days 57–70) were formulated according to National Research Council (1994) [21]. The control group birds (T0) were fed a corn-soybean basal diet (Table 2) for a 70-day, the other three groups were fed this diet supplemented with 300 mg/kg (T300), 400 mg/kg (T400) and 500 mg/kg (T500) curcumin, respectively. The birds were provided with ad libitum access to water and powdered diets. Daylight was eliminated but 24-h constant-light schedule was provided from incandescent bulbs. The house was maintained at 30℃ to 32℃ with a relative humidity of 60–70% at the first 3 days of age. Ambient temperature was gradually reduced by 2 °C to 3 °C every week to a final temperature of 26 ± 1℃ and with a relative humidity of 50–55%.
Table 1
Groups | Basal diet | Curcumin (mg curcumin /Kg basal diet) |
T0 | corn-soybean | 0 |
T300 | corn-soybean | 300 |
T400 | corn-soybean | 400 |
T500 | corn-soybean | 500 |
T0: the group fed with the con-soybean basal diet; T300: the group fed with the con-soybean basal diet + 300 mg/kg curcumin; T400: the group fed with the con-soybean basal diet + 400 mg/kg curcumin; T500: the group fed with the con-soybean basal diet + 500 mg/kg curcumin. |
Table 2
Ingredient composition and nutrient content of the basal diet (%, as-fed basis).
Items | 1–4 weeks | 5–8 weeks | 9–10 weeks |
Ingredient | | | |
Corn (7.9) | 61.70 | 68.94 | 75.80 |
Soybean meal (45) | 26.09 | 26.80 | 20.10 |
Corn protein flour (55) | 7.90 | — | — |
Dicalcium phosphate | 1.40 | 1.40 | 1.40 |
Limestone | 1.08 | 1.06 | 1.06 |
Salt | 0.38 | 0.38 | 0.38 |
DL-Methionine | 0.15 | 0.22 | 0.16 |
L-Lysine | 0.20 | 0.10 | 0.00 |
choline chloride (50%) | 0.10 | 0.10 | 0.10 |
Premix | 1.001 | 1.002 | 1.003 |
Total | 100 | 100 | 100 |
Nutritional level | | | |
Calculated nutrient 4 | | | |
Metabolizable energy (MJ/kg) | 12.14 | 11.98 | 12.21 |
CP (%) | 20.67 | 17.51 | 15.03 |
Calcium (%) | 0.90 | 0.90 | 0.88 |
Total phosphorus (%) | 0.68 | 0.67 | 0.65 |
Non-phytate phosphorus (%) | 0.44 | 0.44 | 0.44 |
Lysine (%) | 1.07 | 0.95 | 0.71 |
Methionine (%) | 0.48 | 0.48 | 0.39 |
Methionine + cystine (%) | 0.81 | 0.75 | 0.63 |
Threonine (%) | 0.75 | 0.66 | 0.56 |
Tryptophane (%) | 0.21 | 0.19 | 0.16 |
1 The premix provided per kilogram diet: vitamin A 4000 IU, vitamin D3 2000 IU, vitamin E 20 mg, vitamin K3 2.0 mg, vitamin B1 2.0 mg, vitamin B2 12 mg, vitamin B6 3.0 mg, vitamin B12 0.02 mg, nicotinic acid 50 mg, D-pantothenic acid 10 mg, folic acid 1 mg, biotin 0.2 mg, Cu 8 mg, Fe 60 mg, Mn 100 mg, Zn 60 mg, Se 0.2 mg, I 0.4 mg. |
2 The premix provided per kilogram diet: vitamin A 3000 IU, vitamin D3 2000 IU, vitamin E 10 mg, vitamin K3 2.0 mg, vitamin B1 1.5 mg, vitamin B2 8 mg, nicotinic acid 30 mg, D-pantothenic acid 10 mg, vitamin B6 3.0 mg, vitamin B12 0.02 mg, biotin 0.1 mg, folic acid 1 mg, Cu 8 mg, Fe 60 mg, Mn 80 mg, Zn 40 mg, Se 0.2 mg, I 0.4 mg. |
3 The premix provided per kilogram diet: vitamin A 2500 IU, vitamin D3 1000 IU, vitamin E 10 mg, vitamin K3 2.0 mg, vitamin B1 1.5 mg, vitamin B2 8 mg, nicotinic acid 30 mg, D-pantothenic acid 10 mg, vitamin B6 3.0 mg, vitamin B12 0.02 mg, biotin 0.1 mg, folic acid 1 mg, Cu 8 mg, Fe 60 mg, Mn 80 mg, Zn 40 mg, Se 0.2 mg, I 0.3 mg. |
4 Values were calculated based on the data provided by Feed Database in China (2004). |
Sample collection
Ducks body weight and feed intake (FI) were recorded during the experiment and then feed conversion ratio (FCR) was calculated. At 70 D of age, one bird near average body weight was selected and slaughtered from per pen after all ducks were fasted for 12 h. The blood sample was collected from the wing veins into heparin sodium tuber. Blood samples were centrifuged at 3,000 × g for 5 min at 4℃ and the obtained plasma was stored at -20℃ for analyzing. The right breast muscle of duck was obtained and analyzed for meat quality.
Assay of antioxidant enzyme activities in plasma
Plasma levels of total antioxidant capacity (T-AOC), total superoxide dismutase (T-SOD), glutathione peroxidase (GPx) and malondialdehyde (MDA) were measured by assay kits (Nanjing Jiancheng Bioengineering Institute, Nanjing, China), respectively, with UV-VIS Spectrophotometer (UV1100, MAPADA, Shanghai, China).
pH and color of duck breast muscle
The pH value of right breast muscle was measured by direct insertion of pH meter electrode (HI9125; Hanna Instruments, Padova, Italy) at 45 min and 24 h after slaughter. The meat color was measured at 45 min and 24 h after slaughter by a colorimeter (Minolta CR-400; Konica Minolta, Tokyo, Japan) using the CIE LAB trichromatic system as L* (lightness), a* (redness), and b* (yellowness), and the average color was obtained via 3 times measuring on the same muscle.
Measurement of drip loss percentage
The breast muscle was weighted after slaughter and suspended in a foam box, and kept 24 h at 4℃, and then the breast muscle was weighted again. The drip loss percent was evaluated as follows:
Where W1 was the original weight of the breast muscle after slaughter (g), W2 was the breast muscle after the loss of natural dripping water at 4℃ for 24 h.
Measurement of cooking loss percentage
Cooking loss is considered as a crucial indicator to evaluate the water holding capacity of breast muscle, and was measured as described by Xiong et al. [22]. The breast muscle was cut and weighted accurately before cooking and cooked in a thin-walled plastic bag with × 10 cm (width) × 15 cm (length) individually in a water bath set at 85℃ until the internal meat temperature reached 75℃ measured by an insertable digital thermometer (MITIR TP600) with stainless steel probe. After cooling to the room temperature (25℃), the cooked muscle surface water was wiped with four layers filter paper, and then weighted immediately. The cooking loss was measured as follows:
Shear force measurement
Shear force of duck breast muscle was measured according to Wang et al. [23] with some modification. The meat samples were cooled to 4℃ after cooking. Two strips with 1.27 mm × 10 mm × 10 mm were cut parallel to the muscle fibers for test. The shear force was conducted by using a tenderization analyzer (C-LM3B tenderization instruments, Northeast Agricultural University, Heilongjiang, China) with a 25 kg load transducer, a crosshead speed of 200 mm/min. The most force value was recorded as the shear force when the duck breast samples were cut.
Thiobarbituric acid reactive substance (TBARS) assay
The TBARS was measured according to the method of Han et al. [24]. The lipid oxidation of duck breast muscle was represented by the TBARS value, and expressed as mg of malondialdehyde (MDA) per kg of duck breast muscle. It is calculated as follows:
Where A532 was the absorbance of the solution measured at 532 nm, Ws was the duck breast meat weight (g), and “9.48” was a constant originated from the dilution factor and the molar extinction coefficient (1.52 × 105 M− 1 cm− 1) of the thiobarbituric acid (TBA) reaction product.
Carbonyl groups content assay
The carbonyl content of myofibrillar protein was detected with 2,4-dinitrophenylhydrazine (DNPH) according to Rababah et al. [25]. The absorbance of the solution at 370 nm was determined to quantify the carbonyl group content expressed as nmol DNPH incorporated mg− 1 meat.
Analysis of volatile compounds
Volatile compounds of duck breast muscle were extracted by solid phase micro-extraction (SPME) in the 20 ml headspace vial (CNW Technologies, Germany) with 3.00 g breast muscle samples according to Wen et al. [26] with mini modification. The headspace vial with 3.00 g breast muscle sample and 4 µL internal standard (IS) substance (100 ppm of o-dichlorobenzene dissolved in methanol) was sealed with PTFE/silicone septum. After equilibrating for 25 min at 45℃, a SPME fiber coated with 75 µm carboxen /polydimethylsiloxane (CAR / PDMS) fiber was inserted into the sample through the septum and exposed to the headspace of the SPME vial for extraction at 45 °C for 40 min. After extraction, the PDMS/DVB/CAR fiber was immediately inserted into the injection port and was then thermally desorbed at 230℃ for 3 min.
A gas chromatography/mass spectrometry (GC/MS) system (QP2020 Shimadzu, Kyoto, Japan) with an InertCapWaX (60 mm × 0.25 mm × 0.25 µm) capillary column was used to analyze the volatile compounds in muscle. Helium as a carrier gas was introduced at a flow rate of 1.0 mL/min. After desorption, the oven temperature was maintained at 40 ℃ for 2 min, then raised to 60℃ at 5 °C/min, 100 °C at a rate of 10 °C/min and ultimately 240 °C at a rate of 18 °C/min for 6 min. The ion source temperatures were 230 °C, and the mass spectrometer scanned from 33 to 450 of the m/z ratios. Identified results were obtained with the semblance degree > 90%. The volatile compounds were semi-quantified by dividing the peak areas of the target compounds by the peak area of the IS and multiplying this ratio by the initial content of the IS (expressed as ng/g).
Statistical analysis
The experiment data were obtained by least six times and analyzed statistically using one-way ANOVA by SPSS (Version 22.0, SPSS Inc., Chicago, USA) with 5% probability of error using the Ducan's multiple comparison among different groups. Statistical significance was P < 0.05. Orthogonal polynomial contrasts were used to determine linear and quadratic responses of Anas Platyrhynchos to different dose levels (0, 300, 400, 500 mg/Kg) of supplemental curcumin.