**3. Results and Discussion**

#### *3.1. Content and Animal Intake of Antioxidant Compounds in Feedstuffs*

Corn is a good source of fat-soluble antioxidant compounds, such as vitamin E and carotenoids [30,31]. Carotenoids are composed of carotenes and xanthophylls, which provide yellow color to animal products [30,31]. The co-products obtained after corn processing, like DG, increase the concentration of corn nutrients, except for sugars [3]. Previous reports have indicated that samples of dried DG with solubles obtained from different plants of bioethanol production have, on average, two-fold higher content of α-tocopherol, γ-tocopherol, and lutein than corn grain [30].

In our study, the content of α-tocopherol was almost three times greater in the dietary treatments with DG inclusion (Table 2) than in the control diet. Other authors have reported that the content of α-tocopherol was 8.0 and 7.4 μg/g in corn-based diets supplemented with 20 and 40% DG respectively and no differences were seen when compared with dry-rolled corn control diet (9.3 μg/g) [32].

**Table 2.** Tocopherol and carotenoid contents (μg/g DM) in feeding diets 1.


<sup>1</sup> Dietary treatment: 0DG, control; 15DG, 15% DG; 30DG, 30% DG and 45DG, 45% DG (%DM basis). <sup>2</sup> SEM: standard error of the mean. <sup>3</sup> Linear (L) and quadratic (Q) response to DG level. Means in the same row having different letters are significant at the *<sup>p</sup>* ≤ 0.05 level. NS: no significant. <sup>4</sup> n.d., not detectable.

Regarding γ-tocopherol, β-carotene, and lutein, their contents increased with the level of DG inclusion in the diets (Table 2). To our knowledge, previous works had analyzed only the content of these compounds in DG alone, as an ingredient, but not in feedstuffs that included DG. Therefore, the values obtained in this work were compared with values reported for complete diets based on corn grain. The values selected for the comparison were those reported by Blanco et al. [33] for total mixed ration (TMR) and corn diets and those by Pouzo et al. [34] for corn diets. The values of lutein observed were similar to those reported for TMR (10.1 μg/g DM), whereas those of γ-tocopherol observed in 15DG, 30DG, and 45DG were higher than the values reported for the corn diet (79.5 μg/g DM, [33] and 14.1 μg/g DM, [34]). Regarding β-carotene, the values observed in all dietary treatments in this study were greater than those reported for the corn diet (1.47 μg/g DM, [34]).

To estimate the vitamin intake of the animals, the composition of the feeding diets was weighted with the consumption of animals (Figure 1). The DM consumption of repetitions and treatments was measured every other week [20] and an average of consumption was calculated for each diet: 8.64 DM/day for 0DG, 8.77 DM/day for 15DG, 8.31 DM/day for 30DG, and 8.17 DM/day for 45DG. No statistical analysis was done on these data since DM intake was recorded on a group basis. Results showed that the intake of antioxidant compounds, except for that of β-carotene, numerically increased with the level of DG inclusion in the diets.

**Figure 1.** Average intake (mean ± SD) of antioxidant compounds weighted with the consumption of the animals, for each dietary treatment (0, 0% DG control; 15, 15% DG; 30, 30%DG; 45, 45% DG, DM basis).

#### *3.2. Antioxidant Compounds in Fresh LTL Muscle*

The diet composition influences animal metabolism, use, and storage of glycogen and accumulation of anti- and pro-oxidant compounds [13,35]. Thus, the feeding diets could affect the content of antioxidant compounds in meat and its susceptibility to oxidative reactions. In our study, the content of γ-tocopherol in meat samples increased with the level of DG (Table 3), which could be explained by the fact that the feeding diets supplied greater content of γ-tocopherol and that the intake of animals increased with the level of DG inclusion. Besides, the content of γ-tocopherol observed was greater than that reported by Pouzo et al. [34], when feeding diets were supplemented with flaxseed.

It has been reported that the supplementation of feeding diets with vitamin E increases the concentration of α-tocopherol in meat [13,32], and that feeding diets including less than 200 μg/g of α-tocopherol produce lamb meat with 1.97 μg/g of α-tocopherol, on average [36]. In our study, although feeding diets were not supplemented with vitamin E, a numerical increase of α-tocopherol was observed in meat samples as the level of DG increased. Salami et al. [37] have recently shown no effect of the inclusion of DG in finishing diets on the content of α-tocopherol in meat. These authors reported that the α-tocopherol content was 2.57 μg/g muscle, on average, i.e., greater than the values observed in our study. However, in their case, the supplementation of DG was in combination with *ad* *libitum* grass silage, which provides greater amounts of α-tocopherol than grain [13]. Other authors have reported that ground beef from animals fed with 20 and 40% of DG in cornbased diets had 1.70 and 1.79 μg/g of α-tocopherol, respectively [32]. In our work, the content of α-tocopherol was lower than the value reported by Da Silva Hampel et al. [36] in the meat of lambs fed with 0–200 μg/g of tocopherol level in the diet; it was only similar (1.41 μg/g) in beef samples from 45DG dietary treatment, which supplied 17.27 μg/g of α-tocopherol.

**Table 3.** Content of antioxidant vitamins and oxidation stability in fresh meat samples (LTL) muscle at 72 h post-mortem.


<sup>1</sup> Dietary treatment: 0DG, control; 15DG, 15% DG; 30DG, 30% DG and 45DG, 45% DG (%DM basis). <sup>2</sup> SEM: standard error of the mean. <sup>3</sup> Linear (L) and quadratic (Q) response to DG level. Means in the same row having different letters are significant at the *p* ≤ 0.05 level. NS: no significant.

In addition to tocopherol, feeding diets supplied carotenoid compounds. These compounds are converted to retinol in the animal and exert antioxidant capacity and contribute to the yellowness of subcutaneous fat [6,12]. The content of carotenoid compounds in meat is highly variable since their incorporation depends on their content in the feeding diets, and the accumulation in adipose tissue, which is related to the type of muscle and the individual uptake capacity of the animal [13,35]. Previously, it has been reported that the content of carotenoids and their retinoid derivatives is at least one order below that of α-tocopherol [13]. In fact, Pouzo et al. [34] reported that meat samples from grazing systems supplemented with corn had 0.09 ug of retinol/g of fresh meat and 1.15 ug of α-tocopherol/g of fresh meat. In our study, the values of retinol observed in meat tended to be greater in samples from DG diets. Additionally, the values observed were one order below the values of α-tocopherol, independently of the dietary treatment (Table 3).

Neither the antioxidant capacity, measured as FRAP, which determines the total reducing capacity of antioxidant compounds nor the lipid oxidation, measured as TBARS, in meat samples at 72 h post-mortem were affected by the level of DG inclusion in the diets (Table 3). In general terms, no differences were seen in meat oxidation stability due to the dietary treatment. Additionally, other authors have observed a lack of effect on lipid oxidation in meat from steers fed 50% DG and aged for 2 days [38]. Interestingly, recently published data have shown that meat from cattle finished on a grass silage-based diet in combination with corn or wheat DG supplementation showed no differences in the FRAP values, after 14 days of aging, regardless of the source of DG [37].
