Chicken meat with a high content of n-3: effect of vitamin e and selenium supplementation

Introduction

The negative impact of the increase of polyunsaturated fatty acids on the stability of lipids in chicken meat has been demonstrated by several investigations. Antioxidants such as β-carotene, vitamin E, vitamin C, essential oil of oregano have been used and evaluated for the purpose of lengthening the shell life of these products (Ruiz et al., 1999, 2001; Nam et al., 1996; Bou et al., 2001; Botsoglou et al., 2003). Selenium has a special place among the natural antioxidants, participating in the regulation of several physiological processes. It also acts in the first line of antioxidant defense, which involves several enzymes, taking a leading role in the activity of the Glutathione peroxidase (Surai, 2002). In the light of this research, we decided to evaluate the protective effect of the organic Se with vitamin E in chicken meat with a high content of n -3.

Materials & Methods

80 commercial line male chickens were fed from birth up to 21 days a standard corn-soy based commercial diet. From the 22nd day four treatments with different sources of n-3 with isocaloric corn-soy based diets were assigned: T1: control diet, T2: linseed oil (4 %), T3: fish oil (2 %) and linseed oil (3%), T4: fish oil (4 %). T1 diet contained 0.44 % of n-3, diets for T2 and T3 contained 1.5% n-3 and for T4 0.95% of n-3. All diets were supplied with vitamin E (200g/t) and organic Se (200g/t). 49 day-old birds were slaughtered in a commercial refrigerated facility and the carcasses were stored in a freezer at - 20 ° C until further analysis. The samples were cooked for 7 minutes on a pre-heated electric double-plate iron grill, which is equivalent to a final internal temperature of 71 ° C, according to the general guidelines of AMSA (1995). On a total of 6 birds the lipid profile was determined and in 10 birds per treatment sensory panel evaluations were made; TBARS and vitamin E content in the muscle. The results were analyzed using ANOVAs and the Duncan test for average separation. In all cases, the significance level used was 0.05.

Results and Discussion

The inclusion of fish oil (T3 and T4) produced an increase in long-chain fatty acids in the breast (Eicosapentaenoic Acid, EPA, docosapentaenoic acid, DPA and docosahexaenoic acid, DHA) with regard to the control (Table 1); these results are consistent with those reported by López-Ferrer et al. (2001). On the other hand, the inclusion of linseed oil (T2), as the only source, produced a significant increase in linolenic acid and DPA, but failed to increase the EPA and DHA. The high content of linolenic acid in T3 can be explained by the inclusion of linseed oil at 2%.

The lipid profile of the leg-thigh showed the same trends as the breast when fish oil was included in the ration (T3 and T4) (Table 2). The inclusion of linseed oil (T2) produced a significant increase in linolenic acid, EPA and DPA. Similarly to the breast, a high content of linolenic acid was observed in T3, produced by the inclusion of linseed oil in the diet; similar results were observed by Azcona et al. (2008).

Table 1. Content of n-3 fatty acids in chicken breast (g fatty acid/100 g fat)

n-3	T1	T2	T3	T4
C18:3	2.64 c	10.88 a	6.84 b	1.58 c
C20:5 (EPA)	0.42 c	0.6 c	1.43 b	1.84 a
C22:5 (DPA)	0.88 b	1.54 a	1.52 a	1.89 a
C22:6 (DHA)	1.12 c	1.3 c	6.17 b	9.39 a
Total	*5.06*	*14.32*	*15.96*	*14.7*

^{Means with unequal letters differ significantly (p < 0.05).}

Table 2. Content of n-3 fatty acids in leg-thigh (fatty acid g / 100 g fat)

n-3	T1	T2	T3	T4
C18:3	2.91 c	12.2 a	8.68 b	1.80 a
C20:5 (EPA)	0.19 d	0.71 c	1.45 b	1.75 a
C22:5 (DPA)	0.67 b	1.34 a	1.48 a	1.37 a
C22:6 (DHA)	0.71 c	1.1 c	4.44 b	5.95 d
Total	*4.48*	*15.35*	*16.05*	*10.87*

^{Means with unequal letters differ significantly (p < 0.05)}.

The TBARS values were higher in those treatments with the addition of fish oil (Table 3) and these treatments, in turn, showed a lower concentration of alpha-tocopherol in the meat (Table 4). This behavior can be explained by the presence of DHA and EPA in oil of marine origin, as well as in the lower concentration of vitamin E found in the meat.

Table 3. Values of TBARS in cooked chicken meat (mg MDA/kg meat)

Treatment	TBARS
T1	0.523 b
T2	0.597 b
T3	1.980 a
T4	1.785 a

^{Means with unequal letters differ significantly (p < 0.05).}

Table 4. Values of alpha-tocopherol in cooked chicken meat (µg/g)

Cut	Alpha-tocopherol
Thigh	32.0 a
Breast	23.7 b
Treatment	Alpha-tocopherol
T1	38.4 a
T2	39.7 a
T3	16.7 b
T4	16.6 b

^{Means with unequal letters differ significantly (p < 0.05).}

We found significant differences in the values of breast (Table 5) for aroma and strange aroma (Table 5). T3 and T4 samples showed aroma values lower than T1 due to the appearance of strange aromas. The samples were described as meat of "somewhat weak" aroma (T1) and of "weak" aroma (T3 and T4). The strange aromas were of "weak" intensity for T3 and T4; they were described as fish/sea/cod and of "very weak" intensity for T1 and as grain/toasted cereal/oil aroma.

Significant differences were also found in the leg-thigh cut. T3 and T4 samples showed aroma values lower than T1 because of the appearance of strange aromas. The samples were described as meat of "somewhat strong" aroma (T1 and T2) and as meat of "somewhat weak" aroma (T3 and T4). Strange aromas are of "weak" intensity for T3 and T4 and are described as fish/fat/stale aroma of "very weak" intensity for T2; in this case there was no consensus among the evaluators on the description of the strange aroma.

We found significant differences in the "flavor" and "off flavor" values for both cuts. In breast, the samples corresponding to treatments 3 and 4 had flavor values lower than the control treatment and treatment 2 due to the appearance of strange flavors ("off flavors"). Samples were graded as meat of "somewhat strong" flavor (treatment 1), as meat of, "somewhat weak" flavor (treatment 2) and as meat of "weak" flavor (T3 and T4). The strange flavors are of "somewhat weak" intensity (treatments 3 and 4) and are described as fish/stale flavor; as of "very weak" intensity (treatment 2) and as cereal/oil/bitter flavor and of "very weak" intensity (treatment 1), and are described as grain/oil. On the other hand, similar behavior was observed in regard to the flavor of the leg-thigh cut, except for T4, where significant differences in flavor compared to T4 became manifest. With regard to the "off flavor", these were of greater intensity but with the same trend as in breast. T3 and T4, in turn, had greater intensity in "off flavor" and were significantly different from T1 and T2.

No statistical differences in tenderness and juiciness among the treatments were found.

Table 5. Features of breast meat obtained from the sensory panel

Treatment	Aroma	Strange aromas	Flavor	Strange flavors	Initial Tenderness	Juiciness
T1	5.50 a	2.01 b	5.08 a	1.78 c	*6.01*	*4.12*
T2	5.31 ab	3.66 a	4.88 a	2.72 b	*6.06*	*4.1*
T3	4.88 b	3.94 a	4.30 b	4.24 a	*6.07*	*4.1*
T4	4.86 b	3.64 a	4.21 b	4.12 a	*6.21*	*4.43*

^{Means with unequal letters differ significantly (p < 0.05).
0 = extremely weak and 10 = extremely intense aroma and flavor.
0 = extremely hard and 10 = extremely tender for initial tenderness.
0 = extremely dry and 10 = extremely juicy for juiciness.}

Table 6. Features of leg-thigh meat obtained from the sensory panel

Treatment	Aroma	Strange aromas	Flavor	Strange flavors	Initial Tenderness	Juiciness
T1	5.81 a	2.03 c	5.57 a	2.73 b	*6.39*	5.62 a
T2	5.66 a	3.02 b	4.83 b	3.01 b	*6.29*	5.15 b
T3	5.03 b	3.86 a	4.26 c	4.64 a	*6.65*	5.73 a
T4	4.77 b	4.25 a	4.08 c	4.66 a	*6.36*	5.56 ab

Conclusions

Meat from chickens fed diets containing linseed oil in showed a sensory profile similar to that expected from commercial chicken meat. On the other hand, the addition of fish alone or in combination with linseed oil, impacted negatively on the sensory aspect and the oxidative status, with the emergence of flavors and odors that may compromise their acceptability by consumers. The combination of antioxidants was not effective in protecting the meat from oxidation in the cooking process, although he diets contained an equal amount of n-3 (T2 = T3) and a lower amount (T4 vs. T2). The higher content of vitamin E would also have contributed to lower TBARS values in the control treatment and the linseed oil treatment, while the meat from birds fed fish oil had a greater concentration of EPA and DHA and a smaller presence of vitamin E in their tissue.

Bibliography

AMSA 1995. American Meat Science Association. Research guidelines for cookery, sensory evaluation and instrumental tenderness measurements of fresh meat. National Live Stock and Meat Board, Illinois.

Azcona JO, Schang MJ, Garcia PT, Gallinger CI, Coates W, Ayerza R. 2008. Omega-3 enriched broiler meat: the influence of dietary α-linolenic-ω-3 fatty acids source on growth, performance and meat fatty acid composition . Can. J. Anim Sci. 88(2):257-269.

Botsoglou NA, Grigoropoulou SH, Botsoglou E, Govaris A, Papageorgiou G. 2003. The effects of oregano essential oil and alfa-tocopheryl acetate on lipid oxidation in raw and cooked turkey during refrigerated storage. Meat Science 65:1193-120.

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Ruiz JA, Pérez-Vendrell AM, Esteve García E. 1999. Effect of B-carotene and vitamin E on Oxidative stability in leg meat of broilers fed different supplemental fats. Journal of Agricultural and Food Chemistry 47:448-454.

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Chicken meat with a high content of n-3: effect of vitamin e and selenium supplementation

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