Manipulation of the fatty acids composition of poultry meat and giblets by dietary inclusion of two oil sources and conjugated linoleic acid

Mudança na composição de ácidos graxos das vísceras e da carne de aves tratadas com uma dieta contendo ácido linoléico conjugado e duas fontes de óleo

VETERINARY MEDICINE

Manipulation of the fatty acids composition of poultry meat and giblets by dietary inclusion of two oil sources and conjugated linoleic acid

Mudança na composição de ácidos graxos das vísceras e da carne de aves tratadas com uma dieta contendo ácido linoléico conjugado e duas fontes de óleo

S.F. Zanini^I; E. Vicente^II; G.L. Colnago^III; B.M.S. Pessotti^IV; M.A. Silva^V

^IDepartamento de Medicina Veterinaria - CCA-UFES, Caixa Postal 16, 29500-000 Alegre, ES

^IIInstituto de Tecnologia de Alimentos Campinas, SP

^IIIFaculdade de Veterinária - UFF Niterói, RJ

^IVAluno de pós-graduação - CCA-UFES Alegre, ES

^VAluno de graduação - CCA-UFES Alegre, ES

ABSTRACT

The effect of dietary conjugated linoleic acid (CLA) in association with two vegetable oil sources on the fatty acids of meat and giblets of broiler chickens was evaluated. Two hundred 21-day-old broiler chickens were distributed in a completely randomized factorial design 2 x 5 (two oil sources, soybean or canola oil; and five levels of CLA, 0.0, 2.5, 5.0, 7.5, and 10.0g/kg). The addition of CLA to the diet resulted in an increase (P<0.05) in CLA deposition in the analyzed tissues. CLA supplementation also reduced (P<0.05) the rate of polyunsaturated to saturated fatty acids in thigh, breast, heart, and gizzard. There was interaction of CLA x oil source (P<0.05). The intake of soybean oil, associated with increasing CLA, resulted in an increase in lipid deposition in edible portions as observed by an increase in the overall content of fatty acids, including CLA, while the use of canola oil, associated with increasing CLA in the diet, resulted in a decrease in lipid content in edible portions, specifically regarding that of saturated fat (P<0.05) in breast meat and liver and in the content of monounsaturated fatty acids (P<0.05) in thigh, breast, liver, and gizzard.

Keywords: broiler, conjugated linoleic acid, canola oil, soybean oil, meat

RESUMO

Avaliou-se o efeito da suplementação de ácido linoléico conjugado (CLA) associado com duas fontes de óleo na dieta de frangos de corte sobre a composição de ácidos graxos das vísceras e da carne de aves. Duzentos frangos de corte, machos, com 21 dias de idade, foram distribuídos em delineamento inteiramente ao acaso, em arranjo fatorial 2 x 5 (duas fontes de óleo, soja e canola e cinco níveis de CLA, 0,0, 2,5, 5,0, 7,5 e 10,0g/kg). A adição de CLA na dieta resultou em aumento (P<0,05) de sua deposição na carne e nas vísceras de aves. Foi observado decréscimo (P<0,05) na taxa de poliinsaturados:saturados nas carnes da coxa e do peito, no coração e na moela com a suplementação de CLA. Houve interação (P<0,05) CLA x fonte de óleo. O uso de teores crescentes de CLA na dieta contendo óleo de soja na dieta resultou em aumento (P<0,05) no conteúdo lipídico. O contrário foi verificado com a utilização de óleo de canola, especificamente no conteúdo de ácidos graxos saturados (P<0,05) na carne do peito e no fígado e de monoinsaturados (P<0,05) nas carnes do peito e da coxa, fígado e moela.

Palavras-chave: frango de corte, ácido linoléico conjugado, canola, soja, carne

INTRODUCTION

The content and composition of fat in meat and giblets are affected by animal feeding, a fact that is exploited in the modification of the composition of the fatty acids in meat, and the best results have been obtained in monogastric animals such as pigs and poultry.

Several studies have shown that conjugated linoleic acid (CLA) influences the composition of meat. Dietary CLA is reported to reduce the content of monounsaturated and polyunsaturated fatty acids in meat (Szymczyk et al., 2001) and increase the concentration of saturated fatty acids (Schafer et al., 2001; Badinga et al., 2003), which is contrary to current dietary recommendations (Nutritional ..., 1990). When CLA is used in diets with oleic, linoleic, or linolenic acids, the undesired effects of increasing saturated fatty acids was reduced (Du et al., 2000; Kim et al., 2007; Martin et al., 2007). The objective of this study is to investigate the effect of dietary CLA associated with oil sources that have different linoleic:linolenic acid ratio (soybean oil and canola oil) on the fatty acids composition of chicken meat and giblets.

MATERIAL AND METHODS

Two hundred 21-day-old male broiler chickens were distributed in a randomized factorial arrangement of 2 x 5 (two oil sources, soybean or canola oil, and five levels of CLA, 0.0, 2.5, 5.0, 7.5, and 10.0g/kg) with four experimental units each (five birds/pen). The source of CLA contained approximately 600g/kg conjugated isomers, as a 50:50 mixture of 18:2 cis-9, trans-11 and 18:2 trans-10, cis-12. The diet supplemented with soybean oil was the control, since this is the standard oil source used in poultry nutrition. The diets had 40g/kg of soybean or canola oil. CLA supplementation levels were obtained by isometrically replacing soybean or canola oil in the basal diets.

From one to 21 days of age, the chicks were raised on a corn-soy diet with 210g/kg protein and 12.34 MJ of metabolizable energy per kg of diet. The basal diet fed from 22 to 45 days of age is shown in Table 1.

The composition of fatty acids present in the oils (Table 2) was determined by gas liquid chromatography, according to Firestone (1998). The samples were subjected to transmethylation and the fatty acids were converted to methyl esters (Hartman and Lago, 1973). The lipids contained in the meat (thigh and breast) and giblets (heart, gizzard, and liver) were extracted using the Folch et al. (1957) technique and the composition of fatty acids was determined by gas liquid chromatography (Firestone, 1998). The composition of saturated, monounsaturated, and polyunsaturated fatty acids was evaluated in the meat and giblets: saturated (C10:0; C12:0; C14:0; C15:0; C16:0; C17:0; and C18:0); monounsaturated (C16:1n-7 and C18:1n-9); and polyunsaturated (C18:2n-6; C18:3n-3; C20:4n-6; C20:5n-3; C22:5n-6; C22:5n-3; and C22:6n-3).

A gas chromatograph Varian 3900, equipped with a flame ionization detector, split/splitles injector, and capillary silica column, coupled to a Star Workstation was used. The injector was operated at 270°C, on split mode with flow of 100ml/min. The oven temperature was 120ºC/5min; 120ºC to 220ºC (3ºC/min); 220 to 235ºC (1ºC/min), and 235ºC/12min. The carrier gas was hydrogen at a constant flow rate of 1.0ml/min and the detector temperature was 310°C.

Each fatty acid was identified in the form of a methyl ester by comparing the retention times with those of the standards. Quantification was made by normalization. In addition, analysis of the CLA-isomers of the oil included in the feed was performed by the method fore cited and quantified as total isomers of CLA. In the case of the poultry meat, the results were expressed in g kg^-1 of edible portion, using the lipid conversion factor reported by Holland et al. (1994). The experimental data was analyzed using the analysis of variance by the SAEG (Sistema..., 1997). Significant differences among means were determined by the SNK test at P<0.05. Regression analysis were used to report the effects of CLA levels. When ANOVA indicated a significant interaction for a certain variable, the effect of oil source within each CLA level was determined.

RESULTS AND DISCUSSION

Addition of CLA in the diet resulted in an increase (P<0.05) in CLA deposition in analyzed tissues (Table 3), which agrees with previous studies (Badinga et al., 2003; Kim et al., 2007; Santos et al., 2007). The highest value for deposition of CLA was detected in the heart tissue and the lowest value for CLA was observed in breast meat (Table 3). The content of CLA of chicken meat varies from 0.03-0.9mg/g (Chin et al., 1992).

The data on the fatty acids composition of the thigh meat are presented in Table 4, for breast meat in Table 5, and for giblets in Tables 6, 7, and ⁸. In the thigh, breast, heart tissue, and gizzard, the highest content of the monounsaturated fatty acids occurred in broilers receiving the canola oil diet which differs (P<0.05) from that of chickens fed soybean oil diet. In contrast, chickens fed soybean oil diets had higher content of polyunsaturated fatty acids and n-6 fatty acids in thigh and breast meats, heart, liver, and gizzard, differing (P<0.05) from that of broilers fed the canola oil diets. Thus, a higher rate (P<0.05) of polyunsaturated:saturated (P:S) fatty acids in thigh (Table 4), heart (Table 6), and gizzard (^{Table 8}), of chickens fed soybean oil diets in comparison to canola oil was observed. The fatty acids composition of lipids from meat and giblets reflected the fatty acids composition of the diet. This information corroborates previous findings (Zanini et al., 2004).

Increasing levels of CLA in the diet produced a linear reduction (P<0.05) in the levels of monounsaturated fatty acids in thigh meat ( = 17.48 - 0.49x, R² = 0.93) and an increase (P<0.05) in saturated fat in the thigh meat (Table 4) and gizzard (^{Table 8}), which agree with a previous report (Kim et al., 2007). However, in the present study, the increase (P<0.05) in the content of saturated fatty acids was only observed in birds fed the soybean oil diets ( = 11.03 + 0.40x, R²= 0.82 for thigh meat; = 10.69 + 1.0x, R²= 0.92 for gizzard). CLA also produced a reduction (P<0.05) in the rate of polyunsaturated:saturated (P:S) in the thigh (Table 4), breast (Table 5), heart (Table 6), and gizzard (^{Table 8}).

Dietary CLA has been suggested to reduce unsaturated fatty acids in meat. CLA is known to decrease the activity and gene expression of stearoyl CoA delta9 desaturase (Choi et al., 2002) and may also suppress delta6 and delta5 desaturase (Chuang et al., 2001a; Eder et al., 2002) and elongase (Chuang et al., 2001b), resulting in accumulation of saturated fatty acids, which leads to a change of the composition of fatty acids in animal tissue (Watkins et al., 2003). Therefore, the modification of the profile of fatty acids in broiler tissue due to dietary CLA seems to be related to a likely inhibition of the desaturation of fatty acids. Also, the findings of the present study reveal that this inhibitory effect of CLA seems to be dependent of the oil source in the diet.

A significant interaction (P<0.05) between oil source and CLA supplementation was observed on lipid content and on fatty acids profile. An increase (P<0.05) in the lipid content was observed and was measured as g/100g in the thigh ( = 3.26 + 0.09x, R²=0.90), heart (P<0.05, = 8.43 - 0.44x + 0.07x², R² = 0.87), liver (P<0.05, = 1.03 + 0.13x, R² = 0.66), and gizzard (P<0.05, = 4.52 + 0.09x, R² = 0.89) of broilers fed increasing levels of CLA plus soybean oil. The opposite was observed in the breast meat (P<0.05, = 0.91 - 0.16x + 0.01x², R² = 0.93). Thus, the increase (P<0.05) in the fat content in the meat and giblets was represented by a linear increase (P<0.05) in the content of saturated fat in the thigh (Table 4), in the heart tissue ( = 16.0 + 2.07x, R² = 0.99), and in the gizzard (^{Table 8}). There was a linear increase (P<0.05) in the content of the monounsaturated fatty acids in the heart (Table 6) and in the gizzard (^{Table 8}), and also in the content of the polyunsaturated fatty acids in these organs ( = 13.61 + 0.83x, R²=0.85 for heart tissue; = 8.07 + 0.32x, R²= 0.82 for gizzard). These changes were accompanied by increases (P<0.05) in contents of ω6 fatty acids in the heart ( = 12.78 + 0.61x, R²=0.78) and in the gizzard, and in the content of ω3 fatty acids in the heart ( = 0.83 + 0.04x, R² = 0.83). The reduction (P<0.05) in total lipids in the breast of birds fed soybean oil diets was associated with increasing levels of CLA (P<0.05), which was represented by a linear decrease (P<0.05) in the deposition of monounsaturated and polyunsaturated fatty acids ( = 2.50 - 0.18x, R²= 0.88), especially ω6 fatty acids ( = 2.11 0.15x, R²= 0.85). The intake of soybean oil diets with increasing CLA also resulted in an increase (P<0.05) of the saturated fatty acids ( = 4.85 - 0.40x + 0.09x², R²=0.88), monounsaturated fatty acids, polyunsaturated fatty acids (= 2.66 0.34x + 0.04x², R²= 0.86), both ω6 fatty acids (= 2.22 0.25x + 0.03x², R²= 0.81), and ω3 fatty acids in liver (Table 7).

Brown et al. (2001) observed that CLA-treated cultures of preadipocyte supplemented with increasing levels of linoleic acid had greater TG contents and greater numbers of larger cells than cultures treated with only CLA. These data demonstrate that the linoleic acid partially reverses attenuation of CLA of TG content, suggesting that these unsaturated fatty acids may compete for incorporation into TG or phospholipid-derived eicosanoids that regulate preadipocyte differentiation.

However, in the present study, the use of canola oil with increasing CLA levels resulted in a reduction (P<0.05) in the total lipids, that was measured in g/100g, in the thigh ( = 4.68 - 0.08x), breast ( = 1.44 - 0.07x, R²=0.78), liver ( = 1.70 - 0.21x + 0.02x²), and gizzard ( = 6.48 - 0.19x). In the heart, the opposite was observed (P<0.05, = 10.54 - 1.06x + 0.15x²). Therefore, the reduction (P<0.05) in total lipids content was represented by a decrease (P<0.05) in the deposition of saturated fatty acids ( = 5.26 - 0.34x, R²=0.99), monounsaturated fatty acids ( = 6.18 - 0.81x + 0.03x², R²=0.98), and ω3 fatty acids ( = 0.15 - 0.01x, R²= 0.91) in the breast. Also, there was a linear decrease (P<0.05) in the content of the monounsaturated fatty acids ( = 25.75 - 0.98x, R²= 0.81), polyunsaturated fatty acids ( = 9.60 - 0.22x, R²= 0.79), ω6 fatty acids (P<0.05, = 8.36 - 0.25x, R²= 0.87), and ω3 fatty acids (P<0.05, = 0.78 - 0.02x, R²= 0.95) in the gizzard. In the liver, there was a decrease (P<0.05) in the deposition of saturated fatty acids and monounsaturated fatty acids at 5.0-7.5g/kg of CLA with canola oil.

It is known that a major factor in the short-term control of hepatic mitochondrial fatty acid oxidation is the inhibition of CPT-I by malonyl-CoA, the end product of the reaction catalyzed by ACC. Considering that the latter enzyme is a key regulatory site of fatty acid synthesis, inhibition of CPT-I by malonyl-CoA allows for an elegant explanation of the coordinated control of partitioning hepatic fatty acids between esterification and oxidation. Priore et al. (2007) investigated the metabolic fate and short-term effects of CLA compared to linoleic acid (LA) on lipid metabolism. A significant increase in the activity of carnitine palmitoyltransferase I (CPT-I) was observed when compared to the untreated cells, both in CLA or linoleic acid (LA) treated hepatocytes. However, no significant difference was detected between CLA- or LA-induced CPT-I stimulation. In addition, acetyl-CoA carboxylase (ACC) activity was significantly decreased by CLA when compared to the untreated and LA-treated cells. Also, the CLA-treated hepatocytes had the lower content of malonyl-CoA when compared with untreated and treated cells with LA. Contrary to CLA, the LA had no significant effect on both ACC activity and malonyl-CoA level, showing that LA could regulate only liver fatty acids oxidation by increase of CPT-I activity. Also, it was shown that rat hepatocytes produce more CO₂ and acid-soluble products from CLA than from LA. These data showed individual effect of CLA and LA on lipid metabolism. It is worthy noting that, in the present study, there was interaction between CLA and oil source in the lipid content of meat and giblets (P<0.05). It is also noteworthy that the oils used in the diet had different contents of linoleic acid - C18:2ω6 (Table 2) and as such this probably influenced the results. It is therefore suggested that the action of CLA could be attenuated by the addition of high levels of linoleic acid which was also shown in a previous report (Brown et al., 2001). In summary, the effects produced by CLA are dependent upon other dietary factors such as the composition of the oil source.

CONCLUSIONS

Feeding CLA to broilers promoted the incorporation of CLA into muscle tissue and giblets and provides a potential CLA-rich source for human consumption. The intake of soybean oil with CLA resulted in an increase in the overall content of fatty acids, including CLA, due to an increase in the lipid content. The benefits of CLA in canola oil-based diet was the replacement of saturated and monounsaturated fatty acids by CLA with reduction in the lipid content.

ACKNOWLEDGMENTS

The authors are grateful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support and to the BASF Animal Nutrition and Bunge Foods S.A. for technical support.

Recebido em 8 de fevereiro de 2008

Aceito em 22 de setembro de 2008

E-mail: [e-mail]

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Publication Dates

• Publication in this collection
  09 Feb 2009
• Date of issue
  Dec 2008

History

• Received
  08 Feb 2008
• Accepted
  22 Sept 2008