In vitro antioxidant capability and performance assessment of White Roman goose supplemented with dried Toona sinensis

ABSTRACT

Toona sinensis (TS) leaf is a well-known traditional oriental medicine herb. The purpose of this study was to evaluate in vitro antioxidant capability and performance assessment of White Roman goose supplemented with dried TS leaves (TSL). The TSL extracts contained 22.23 ± 1.13 mg gallic acid equivalent/g dry weight (DW) and 1.38 ± 0.06 mg quercetin equivalent/g DW of total phenolics and flavonoid contents. The scavenging action of 1, 1-diphenyl-2-picrylhydrazyl free radical and superoxide anion was as good as that of the butylated hydroxytoluene (BHT) and ascorbic acid, respectively. Inhibition of lipid peroxidation of TSL extracts at 2.5 mg/mL reached nearly 40% compared with the BHT. One hundred and eight White Roman geese aged 6 weeks were distributed to six pens randomly, and fed a grower diet ad libitum during the growing period, with each pen containing nine males and nine females following completely randomized design. Diets were supplemented with the following levels of dried TSL: 0% (control), 0.1% or 0.2% groups for 6 weeks, respectively. The results revealed no significant effects among treatments in the growth performance, blood biochemical parameters and muscle fibre of the grower geese. Superoxide dismutase (SOD) content of the serum in the 0.2% TSL group was significantly higher than that of the control group. In conclusion, dried TSL powder has antioxidative effects in vitro and could serve as a promising natural feed additive to improve the serum SOD content of grower geese.

KEYWORDS:

• Toona sinensis
• antioxidant properties
• growth performance
• White Roman goose

1. Introduction

Toona sinensis (syn. Cedrela sinensis A. Juss.; TS) belongs to the Meliaceae family; it is a well-known traditional Chinese medicine herb. The compounds identified from TS possess a wide range of biologic functions, such as antioxidant activities, hypoglycemic effects and anti-low density lipid glycative activity (Chao et al. 2014; Chen et al. 2014; Liu et al. 2014b). Yang et al. (2014b) pointed out five flavonols and three derivatives of gallic acid which have strong antioxidant activity and scavenge superoxide free radicals.

Currently, consumers are increasingly aware of the nutritional quality of the foods they consume. Farm animal products, such as geese, are important sources of nutrients for human; consumption and health demands have changed from quantity to quality. Today's domestic fowl producers are confronted with numerous challenges to prevent diseases and maintain health without the use of sub-therapeutic antibiotics (Webb & O'Neill 2008). In Taiwan, according to statistical data from the Council of Agriculture, Executive Yuan (2012), involving 4.93 million geese slaughtered for meat. The major breed of meat geese in Taiwan is the White Roman goose, which represents 97.0% of the market product, the other 3% is provided by Chinese goose. As food/feed safety and animal welfare concerns continue to improve, researchers seek better antibiotic alternatives for domestic geese than those currently used (Yang et al. 2014a).

Oxidative rancidity is one of the major causes of deterioration of feed/food for consumption, and it typically causes losses in the production performance. Leeson (2007) showed that the reactive oxygen species could cause lipid peroxidation and oxidative stress of animals, which may lead to metabolic disorders. Improved oxidative status in the living animals and increased oxidative stability of the raw products are considered to be beneficial for consumers. Feed additives have been proven to improve the performance and production quality of poultry and livestock (Ansari et al. 2012; Lee & Yu 2013; Lee et al. 2013). The use of synthetic antioxidants in animals to improve meat quality is being seriously considered. However, because some agents could exert some mutagenic effects at high doses, the innocuousness of these compounds has been questioned. Natural antioxidants such as phytogenics (Chinese medicine herbs) are currently receiving considerable attention in human and animal nutrition fields due to their association with food/meat quality characteristics (Ansari et al. 2012; Huang et al. 2012).

To our knowledge, little information is available regarding the influence of dietary supplementation of dried TS leaves (TSL) powder in the grower geese's diet. Therefore, the objective of the present study was to investigate the in vitro antioxidant capability and performance assessment of White Roman goose supplemented with dried TSL powder.

2. Materials and methods

2.1. In vitro antioxidant capability

2.1.1 TS sample preparation

TSL used in this study were kindly provided by a local TS producer in Changhua, Taiwan. The fresh TS was dried in a forced air dryer at 40°C for 24 h and then ground to a powder (approximately 1 mm in size) prior to its addition to the feed. The extracts were added to 100% distilled water (1:10, w/v) at 95°C for 2 h after filtering (Advantec NO. 1, Tokyo, Japan). The filtrate was evaporated until dry under vacuum conditions. The lyophilized extracts were rehydrated and the concentration adjusted to 1 mg/mL for subsequent analysis.

2.1.2 Bioactive components assay

Total phenolic contents were determined using a Folin-Ciocalteu reagent according to the method as described previously (Kujala et al. 2000). The Folin-Ciocalteu reagent was mixed evenly with TSL extracts before adding the Na₂CO₃ solution, and was measured with a spectrophotometer (HITACHI U-2900, Tokyo, Japan) at 730 nm. Then, with the contents of the phenolic compounds of the extracts, a microgram of the gallic acid equivalent (GAE) was determined using an equation that was obtained from the standard gallic acid graph. The flavonoid content of TSL extracts was determined by following the colorimetric method. Briefly, 0.5 mL of TSL extracts in methanol were mixed with methanol, 10% aluminium chloride and 1 M potassium acetate, and left for 20 min at room temperature. The absorbance of the reaction mixture was measured at 415 nm with a spectrophotometer, and the calibration curve was obtained by preparing quercetin solutions (Chang et al. 2002).

2.1.3 1, 1-Diphenyl-2-picrylhydrazyl (DPPH) free radicals and superoxide anion radicals scavenging capacity assay

The free radical scavenging activity of TSL extracts was measured by DPPH using the method of Blois (1958). Briefly, 0.1 mM solution of DPPH in ethanol was prepared and phosphate buffered saline extracts were added at different concentrations. After 20 min, absorbance was measured at 517 nm and was again used as a control butylated hydroxytoluene (BHT). Lower absorbance of the reaction mixture indicated higher free radical scavenging activity, and was calculated using the following equation:where A0 was the absorbance of the control reaction and A1 was the absorbance in the presence of TSL extracts.

Superoxide anion scavenging activity of TSL extracts was based on the method described by Nishimki et al. (1972). The superoxide radicals were generated in Tris-HCl buffer (16 mM, pH 8.0) containing 600 µM of nitroblue tetrazolium; 1872 µM of dihydromicotineamidadenibe dinucleotide and sample solution of TSL extracts were mixed. The reaction had a further 240 µM of phenazine methosulphate added and left to rest at room temperature for 5 min. The absorbance was measured at 560 nm in a spectrophotometer with ascorbic acid used as a control. Decreased absorbance of the reaction mixture indicated increased superoxide anion scavenging capacity. The percentage inhibition of superoxide anion generation was calculated using the following formula:where A0 was the absorbance of the control, and A1 was the absorbance of TSL extracts.

2.1.4 Lipid peroxidation assay

The lipid peroxidation method described was modified slightly by Duh et al. (1999). Lecithin (300 mg) was sonicated in an ultrasonic cleaner (BRANSON 5210, Danbury, USA) in 30 mL of a 50 mM phosphate buffer (pH 7.4) for 4 h. To the sonicated solution (0.5 mL, 10 mg lecithin/mL), FeCl₃ (0.5 mL, 1 mM), ascorbic acid (0.5 mL, 400 mM) and TSL extracts were added. The mixture was incubated for 1 h at 37°C, and oxidation was measured using the 2-thiobarbituric acid (TBA) method. The absorbance of the sample was read at 532 nm against a negative control, which contained all reagents except lecithin; BHT served as the positive control.

The inhibition of lipid peroxidation percentage equalled [1–(A1/A0)] × 100 where A0 was the absorbance of the negative control reaction, and A1 was the absorbance in the presence of TSL extracts/BHT.

2.2 Animals and experiment design

The experimental protocols for all geese were approved by the Animal Care and Use Committee according to the Regulations of Laboratory Animals, Council of Agriculture in Taiwan. The geese were reared in Changhua Animal Propagation Station, Livestock Research Institute (CAPS-LRI, located at 23°51'N and 120°33'E), Changhua, Taiwan. One hundred and eight White Roman geese aged 6 weeks were distributed to six pens randomly. Before the 6 weeks of age, the rations provided were starter containing apparent metabolizable energy (AME) 2900 kcal/kg and crude protein (CP) 20% for birds during 0–6 weeks old and grower containing AME 2800 kcal/kg and CP 15% for birds during 7–14 weeks old. The rations and drinking water were freely accessible for the birds at all time. Each pen contained nine males and nine females following completely randomized design. They were fed diets supplemented with the following levels of dried TS: 0% (control group), 0.1% (A group) or 0.2% (B group) groups for 6 weeks, respectively. During the experimental period, the geese experienced a natural photoperiod and day length of 11.0–12.0 h. The controlled-environment finishing house was 1.26 m² per goose. The pen of the finishing house was 11.9 × 3.8 m (45.2 m²). It contained a wire floor and one tank and two water dispensers. In the experimental period, the geese were fed a grower diet (Table 1) formulated to meet the nutrient requirements according to the National Research Council (1994); drinking water was provided ad libitum.

Table 1. Ingredients and nutrient compositions of the experimental diet.

Ingredient	Control	A group	B group
	-------------------%-----------------
Yellow corn	64.25	64.15	64.05
Soybean meal (44%)	21.5	21.5	21.5
Wheat bran	5	5	5
Cane molasses	3	3	3
Salt	0.3	0.3	0.3
Dicalcium Phosphate	0.8	0.8	0.8
Limestone, pulverized	1.60	1.60	1.60
Choline Chloride, 50%	0.1	0.1	0.1
Dried power of TS	–	0.1	0.2
DL-Methionine	0.20	0.20	0.20
Rice bran	3	3	3
Vitamin premix^a	0.1	0.1	0.1
Mineral premix^b	0.15	0.15	0.15
Total	100	100	100
Calculated values
CP, %	15.5	15.5	15.5
Metabolizable Energy, kcal/kg	2800	2800	2800
Calcium, %	0.73	0.73	0.73
Phosphorus, %	0.64	0.64	0.64
Lysine, %	0.81	0.81	0.81
Methionine, %	0.47	0.47	0.47
Cystine, %	0.27	0.27	0.27
Tryptophan, %	0.20	0.20	0.20

^aDiets contained per kilogram of diet: vitamin A, 8000 international unit (IU); vitamin D, 1500 IU; riboflavin, 4 mg; cobalamin, 10 μg; vitamin E, 15 mg; vitamin K, 2 mg; choline, 500 mg; niacin, 25 mg.

^bDiets contained per kilogram of diet: manganese, 60 mg; zinc, 50 mg; iron, 50 mg/kg; copper, 3 mg/kg and selenium, 0.26 mg/kg.

2.2.1 Growth performance and blood sampling

At the end of 12 weeks, the performance of the grower geese was assessed by measuring the feed intake and body weight (BW); the BW gain and feed conversion ratio were recorded. On the same day, 12 geese (6 males and 6 females) from each treatment (6 geese per pen) were randomly selected according similar weight and blood samples were obtained by jugular venipuncture from each goose. Blood samples were centrifuged at 3000 × g for 30 min at 4°C; samples were then stored at –20°C until analysed.

2.2.2 Serum biochemical determinations

Serum biochemical values of geese were measured by automatic biochemical analyzer (Hitochi, 7150 auto-analyzer, Hitachi, Tokyo, Japan). A spectrophotometer was used to colorimetrically assay the activities of superoxide dismutase (SOD) and Trolox equivalent antioxidant capacity (TEAC) (Wheeler et al. 1990; Lee et al. 2012). The procedures were conducted with assay kits that were purchased from Cayman Chemical Co. (Ann Arbor, MI, USA). All of the samples were measured in triplicate and at appropriate dilutions to allow the enzymatic activities to achieve the linear range of standard curves. Antioxidative enzyme activities were expressed as unit (U) per millilitre of serum.

2.2.3 Muscle fibre tissue analysis

Before geese slaughter, electrical stunning and bleeding carotid artery were done. Right breast meat tissue were further processed, embedded in paraffin, cut at 2 μm by microtone (Leica RM 2145, Nussloch, Germany), stained with Hematoxylin & Eosin (H&E) staining and evaluated under light microscope (BX-51, Olympus, Tokyo, Japan) and image Pro-plus processing software (Image Pro-Plus, CA, USA) for muscle fibre evaluation.

2.3 Statistical analyses

The data of the variables collected were statistically analysed using the general liner models procedure of SAS software (2004) following a random arrangement.

The mathematic model was:where is the observed response of bird in a pen; µ theoverall mean; the fixed effect of TS supplementation and the residual error when pen was regarded as experimental unit, .

The mean values were compared between three TS supplementations using the least square means with the significant level at p < .05.

3. Results

3.1 Bioactive components assay

The analysis of the active ingredients of TS is given in Table 2. The TSL extracts contained 22.23 ± 1.13 mg GAE/g dry weight (DW) and 1.38 ± 0.06 mg quercetin equivalent/g DW of total phenolics and flavonoid contents.

Table 2. Analysis of the active ingredients of TS.

Ingredients	Total phenolics (mg GAE/g DW)	Flavonoid (mg QE/g DW)
TS	22.23 ± 1.13	1.38 ± 0.06

Notes: The value is expressed as the mean ± standard deviation (n = 5). DW, dry weight; GAE, gallic acid equivalent; and QE, quercetin equivalent.

3.2 DPPH free radicals and superoxide anion radicals scavenging capacity and lipid peroxidation assay

The DPPH free radicals and superoxide anion radicals scavenging activity of TS are shown in Figure 1. The scavenging capacity of DPPH free radical (Figure 1(a)) and superoxide anion (Figure 1(b)) was as good as that of the BHT and ascorbic acid, respectively. The liposome oxidation assay of TS is presented in Figure 2. The results shows that the inhibition of lipid peroxidation of TSL extracts at 2.5 mg/mL reached nearly 40%.

Figure 1. The DPPH free radicals scavenging activity of TS and BHT (a); The superoxide anion radicals scavenging activity of TS and ascorbic acid (b). Each value represent Mean ± SD (n = 5).

Figure 2. Liposome oxidation assay of TS and BHT. Each value represent Mean ± SD (n = 5).

3.3 Growth performances and serum biochemical determinations

The effect of TS on growth performance in grower geese at 7–12 weeks is given in Table 3. The results reveal no significant affects among the treatments in the growth performances of grower geese (p > .05). Otherwise, it indicates that the BW before 6 weeks and BW gain during 7–12 weeks in male was significantly heavier than that of female (p < .05). The effect of TS on blood biochemical parameter in grower geese at week 12 is given in Table 4. The results present no significant effects among treatments in the blood biochemical parameter of grower geese (p > .05). The effect of TS on serum antioxidant enzyme activities in grower geese at week 12 is given in Table 5. It indicates that the SOD content of the serum in the 0.2% TS group was significantly higher than that of control group (p < .05). Moreover, the results reveal no significant affects among the sex treatments in the SOD and TEAC contents of grower geese (p > .05).

Table 3. Effect of TS on growth performance in grower geese at 7–12 weeks.¹

Item	Treatment				Sex			T^4	S	T × S
	0%	0.1%	0.2%	SEM^2	Male	Female	SEM^3
BW, kg/ bird
Initial (6th week)	2.78	2.84	2.78	0.06	2.91^a	2.69^b	0.05	0.704	0.003	0.631
12 week	4.67	4.76	4.61	0.08	4.96^a	4.39^b	0.07	0.465	0.001	0.834
BW gain, kg/bird
7–12 week	1.89	1.92	1.83	0.06	2.05^a	1.70^b	0.05	0.752	0.001	0.489
Feed consumption, kg feed/bird
7–12 week	12.0	12.2	12.0	0.21	–	–	–	0.925	–	–
					–	–	–		–	–
Feed conversion ratio, kg feed /kg gain
7–12 week	6.43	6.36	6.58	0.26	–	–	–	0.898	–	–

Notes: Means within the same rows in the same time but without the same superscript are significantly different (p < .05).

¹Results are given as the means of 2 pens for 18 geese each pen.

²SEM = standard error of the TS treatment mean.

³SEM = standard error of the sex treatment mean.

⁴T: Toona sinensis treatment. S: sex treatment. T × S: Toona sinensis × sex interaction.

Table 4. Effect of TS on blood biochemical parameter in grower geese at week 12.^a

Item	Treatment				Sex			T^d	S	T × S
	0%	0.1%	0.2%	SEM^b	Male	Female	SEM^c
WBC, 10^3/μL	270	268	276	3.20	272	271	2.61	0.223	0.587	0.558
RBC, 10^6/μL	2.09	2.04	2.03	0.05	2.10	2.01	0.04	0.621	0.130	0.605
HB, g/dl	11.5	11.4	11.1	0.17	11.5	11.2	0.14	0.320	0.109	0.157
HT,%	34.5	34.3	33.4	0.62	34.6	33.5	0.51	0.431	0.129	0.244
MCV, fl	165	168	165	1.33	165	167	1.09	0.319	0.423	0.393
MCH, pg	55.2	56.0	54.9	0.70	55.0	55.8	0.58	0.542	0.322	0.564
MCHC, g/dl	33.4	33.4	33.3	0.28	33.2	33.5	0.23	0.967	0.457	0.85
PLT, 10^3/μL	3.08	2.58	2.42	0.87	2.06	3.33	0.71	0.859	0.230	0.859
GLU, mg/dl	82.5	85.1	82.3	1.90	83.5	83.11	1.55	0.538	0.865	0.198
BUN,mg/dl	4.17	4.25	4.17	0.16	4.11	4.28	0.13	0.920	0.404	0.225
CREA, mg/dl	0.26	0.25	0.27	0.02	0.25	0.26	0.01	0.833	0.688	0.161
UA, mg/dl	3.01	2.69	3.61	0.36	2.89	3.32	0.29	0.245	0.330	0.787
GOT, U/L	26.3	25.9	28.3	2.78	24.4	29.3	2.27	0.825	0.161	0.711
GPT, U/L	14.8	13.6	13.9	1.04	12.8	15.3	0.85	0.720	0.058	0.382
TP, g/dL	5.52	5.51	5.38	0.13	5.48	5.46	0.11	0.742	0.914	0.362
ALB, g/dL	2.63	2.65	2.64	0.04	2.63	2.65	0.04	0.965	0.753	0.524
GLO, g/dL	2.88	2.86	2.74	0.09	2.84	2.81	0.08	0.568	0.769	0.359
A/G	0.92	0.93	0.97	0.02	0.93	0.95	0.02	0.281	0.471	0.532
TG, mg/dL	185	197	200	7.11	197	191	5.80	0.345	0.519	0.629
TC, mg/dl	174	162	185	11.9	172	175	9.72	0.441	0.846	0.835
HDL, mg/dl	87.5	95.2	91.3	3.54	93.2	89.5	2.89	0.333	0.395	0.994
LDL, mg/dl	73.8	81.8	83.7	4.91	80.9	78.6	4.01	0.354	0.687	0.501
IgG, mg/d	121	120	121	1.51	120	121	1.23	0.847	0.903	0.821

Notes: WBC, white blood cell; RBC, erythrocyte; HB, haemoglobin; HT, hematocrit; MCV, HT/RBC; MCH, HB/RBC; MCHC, HB/HT; PLT, platelet; GLU, glucose; BUN, blood urea nitrogen; CREA, creatinine; UA, uric acid; GOT, glutamyl oxaloacetic transaminase; GPT, glutamyl pyrubic transaminase; TP, total protein; ALB, albumin; GLO, globulin; TG, triglycerides; TC, total cholesterol; HDL, high density lipid; LDL, low density lipid; and IgG, immunoglobulin G.

^aResults are given as the means of 2 pens for 18 geese each pen.

^bSEM = standard error of the TS treatment mean.

^cSEM = standard error of the sex treatment mean.

^dT, Toona sinensis treatment; S, sex treatment; and T × S, Toona sinensis × sex interaction.

Table 5. Effect of TS on serum antioxidant enzyme activities in grower geese at week 12.¹

Item	Treatment				Sex			T^4	S	T × S
	0%	0.1%	0.2%	SEM^2	Male	Female	SEM^3
SOD^5 (U/ml)	29.6^b	31.1^ab	33.9^a	1.06	31.8	31.5	0.85	0.027	0.810	0.117
TEAC^5 (U/ml)	21.8	22.6	22.8	0.36	22.3	22.5	0.31	0.204	0.751	0.224

Notes: Means within the same rows in the same time but without the same superscript are significantly different (p < .05).

¹Results are given as the means of 2 pens for 6 geese each pen.

²SEM = standard error of the TS treatment mean.

³SEM = standard error of the sex treatment mean.

⁴T: Toona sinensis treatment. S: sex treatment. T × S: Toona sinensis × sex interaction.

⁵SOD and TEAC represent the superoxide dismutase and trolox equivalent antioxidant capacity, respectively.

3.4 Muscle fibre tissue analysis

The effect of TS on muscle fibre in grower geese at week 12 is shown in Figure 3. The results reveal no significant effects between the control and 0.2% TS groups by H&E stain for muscle fibre of grower geese (p > .05).

Figure 3. Effect of TS on muscle fiber in grower geese at week 12. (a) Control group (0%); (b) Control group (0%) (H&E stain, 100×); (c) 0.2% TS group (H&E stain, 100×).

4. Discussion

Herbal remedies or botanicals were added to the animal diets to stimulate the performance and/or to enhance the antioxidant system (Ansari et al. 2012; Lee et al. 2013; Chao et al. 2014). The TS are usually used as a vegetable and traditional Chinese medicine herb in China. Chao et al. (2014) and Hseu et al. (2008) showed that the TSL extracts and gallic acid possess effective antioxidant capacity against various oxidative systems in vitro, including the scavenging of free radicals and superoxide anion radicals, metal chelation and reducing power. Chen et al. (2012) presented that the chelating capacities of ferrous ion in the TSL extracts obtained from different solvent concentrations were above 80% and mentioned its extracts could be used as biopreservatives of food product. Huang et al. (2014) also pointed out that dried TSL could reduce the lipid oxidation as represented by TBA reactive substances in toona barbecue sauce, and the main antioxidative constituents are gallic acid and its derivatives, and flavonol glycosides might play an important role in its antioxidant activity in TS. Wang et al. (2007) showed that the main antioxidative constituents in the TS are gallic acid and its derivatives; gallotannins and flavonol glycosides might play an important role in the antioxidant activity of this tree vegetable. Otherwise, total phenolic contents’ main function is the redox reaction, which plays an important role in neutralizing/adsorbing those free radicals such as superoxide anion (O₂·–) radicals, hydroxyl (·OH) radicals, and hydrogen peroxide (H₂O₂, as oxygen in non-free radical state) for minimizing the damage to cells and inhibiting lipid oxidation (Parr & Bolwell 2000). Gulcin (2005) analysed the superoxide anion scavenging capacities of black pepper seeds and used the ascorbic acid as a control. The results pointed out that the scavenging abilities of pepper seeds, upon being extracted by water and ethanol, were 64.2% and 22.6%, respectively, for ascorbic acid when the concentration of extracts was 0.075 mg/mL. In comparing TSL extracts, superoxide anion was as good as that of the ascorbic acid, indicating that TSL extracts had a better superoxide anion scavenging abilities than the black pepper seeds extracts. Therefore, in this study, we demonstrated that dried TS powder has high total phenolic contents and antioxidative capacities by in vitro evaluation.

Liao et al. (2006) pointed out that there was no significant difference in BW, feed intake and organ weights with 1.0% TSL root or bark supplemented in the mice's diet. Wang et al. (2014) demonstrated that TSL could inhibit microglia-mediated neuroinflammation, but not cause cytotoxicity. Liao et al. (2009) indicated that TS extracts have no significant toxic effect in regard to the parameters of body and organ weight in rats, as well as hematological, biochemical and urinary effects. In this study, the results also reveal no significant effects on growth performance with 0.1% and 0.2% dried TS powder supplemented in the grower geese. Tilki et al. (2005) indicated that the difference in live weight between the sexes became significant statistically at 6, 8, 10, 12, 14 and 16 weeks of age. Çelik and Bozkurt (2009) presented that the BW of geese, abdominal fat, hot and cold carcass and mean values of hot and cold carcass were higher in males than females. It is displayed by the male and female geese weight difference; therefore, in this study, the treatment with sex show no interaction effect. Meanwhile, the muscle fibre pattern results reveal no significant effects between control and 0.2% TS group in grower geese.

Antioxidant enzymes are synthesized and regulated endogenously (Giannenas et al. 2010). One of them, SOD which is regulated and synthesized endogenously antioxidant mechanisms, are an important index of antioxidant capacity of animal/human tissue (Jiang et al. 2007); moreover, SOD catalyses the dismutation of the superoxide anion (O^2–) into hydrogen peroxide, and prevents the generation of free radicals. TEAC measures the capacity of a compound to capture 2,2'-azinobis- (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), a radical cation. Botanical extracts such as isoflavone from soybean have been shown to increase the TEAC and SOD content of the plasma of chickens, and decrease lipid peroxidation (Jiang et al. 2007). Brenes et al. (2008) demonstrated that the inclusion of 3.0% of grape pomace concentrate increased antioxidant activity (using ABTS method) in broiler serum and excreta. Moreover, Liu et al. (2014a) found that supplementation with quercetin, which is well known for rich phenolic components and high antioxidant effects, could increase chickens’ SOD activity. Yang et al. (2014a) showed that aqueous extracts of TS improved functions of sperm and testes for male rats under oxidative stress. In this study, high antioxidant activity of TS could better increase the serum SOD content than the control group in the 0.2% TS group; hence, it may suggest that natural secondary metabolites found in the aforementioned extracts affect gene expression of antioxidant enzymes (Puiggross et al. 2005).

5. Conclusion

Based on the results, it may be concluded that dried TS powder has antioxidative effects in vitro and could serve as a promising natural feed additive to improve the serum SOD content of grower geese.

Disclosure statement

No potential conflict of interest was reported by the authors.