Orientadora:Profa. Dra. Andresa Carla Feihrmann

Data da Defesa: 27/09/2019

 INTRODUCTION. Studies have shown that heat stress before slaughter can affect meat quality as well as its functional properties (Almeida, 2007; Zhang et al., 2015; Loyau et al., 2015). In addition, it has also been related to changes in the antioxidant system. Several studies have shown the beneficial effect of methionine supplementation on the activity ofdifferent antioxidant components of heat stressed birds (Del Vesco et al., 2015; Gasparinoet al., 2018).
AIMS. Therefore, this project aimed to evaluate the effects of methionine supplementationin free form and dipeptide on meat quality parameters, total antioxidant capacity, proteinand lipid oxidation, and expression of the isoform 3 ryanodine receptor gene (RYR3) in the breast muscle of broilers with 35 days old or not submitted to heat stress (32 ° C) 24 hours before slaughter.
MATERIAL AND METHODS. Ninety-six chickens were distributed in a completely randomized experimental design in a 3 x 2 factorial scheme with four replications per treatment, being three diets: SM = diet not supplemented with methionine, DL = diet supplemented with DL-methionine (99%) as free amino acid and MM = diet supplemented with dipe. methionine peptide DL-methionyl-DL-methionine (95%), and two environments: CT = thermal comfort and EC = heat stress (32ºC) for 24 hours. The pH and instrumental color in the muscle were evaluated after 24 h post mortem. The moisture percentage was quantified by the volatilization gravimetry method, and the mineral residue content was determined by combustion at 550 ° C for 5 hours, according to the methodology proposed by AOAC (2005). The total nitrogen quantification in the samples was obtained by the Kjeldahl method, using 6.25 as the correction factor for the calculation (AOAC, 2005). Total lipids were extracted using a mixture of chloroform and methanol according to the method of Bligh & Dyer (1959). For the determination of water retention capacity (CRA), the methodology described by Nakamura and Katoh (1985) was used. The shear force of fresh chicken breast meat was performed using a TA-XTU plus texture analyzer model (Stable Micro Systems, Surrey, England) equipped with the Warner- Bratzler (WB) speed calibrated standard shear blades. 2 mm / s and 5 mm / s return speed according to Wheeler et al. (1997). Total antioxidant capacity (TAC) in plasma was quantified via stable free radical scavenging activity 2,2-diphenyl-1-picrylhydrazyl (DPPH - Sigma-Aldrich) according to the method described by Janaszewska and Bartosz (2002), with some modifications. Lipid oxidation was quantified by the 2-thiobarbituric acid reactive substances (TBA) method and protein oxidation was quantified by carbonyl group determination, according to the methodology described by Levine et al. (1990), modified. The gene analyzed was the isoform 3 ryanodine receptor (RYR3). CDNA was amplified using gene-specific primers analyzed by real-time PCR and analyzed by agarose gel electrophoresis. The 2-ΔCT method w s used nd to ev lu te the normality of the data the UNIVARIATE procedure was applied. Means were compared using the Tukey test (p<0.05).
RESULTS AND DISCUSSION. To calculate muscle yield, it was observed that diet influenced breast yield (P <0.01). The broilers consuming the SM diet presented lower breast yield (~ 21%) when compared to the animals consuming the diets supplemented with methionine (DL and MM). The animals consuming the SM diet presented higher pH and a * values. There was an interaction effect between diet and environment on parameter b * (P = 0.04), animals under heat stress and consuming the SM diet presented the lowest value of b *. No effect of treatments on L * parameter (P> 0.05) was observed. It was verified that the diet influenced the nitrogen and lipid content of the chest muscle (P = 0.03 and P <0.01, respectively). The animals supplemented with methionine (DL and MM) presented higher nitrogen content and lower total lipid content compared to animals that consumed the SM diet. There was no effect of diet on moisture content, ash, CRA and shear strength (P <0.05). It was observed that the environment influenced the humidity of the breast, and it was verified that the animals submitted to the environment of EC presented lower humidity value. We did not verify environmental effect on the ash content, nitrogen, lipids, CRA and shear force (P> 0.05). It was observed that on the seventh day of analysis there was effect of diet (P = 0.03) and environment (P < 0.01), and the animals that consumed the diet with methionine dipeptide (MM) had the lowest malonaldehyde content (~ 23% lower malonaldehyde content than animals that consumed the SM diet). It was verified that the diet influenced the TAC (P = 0.04), being observed that the animals consuming the MM diet presented higher value of TAC. No effect of diet on protein oxidation was observed (P = 0.37). We also observed environmental effect on TAC (P = 0.01) and protein oxidation (P = 0.03). The animals submitted to the EC environment showed an approximately 12% reduction in CAT and an approximately 13% increase in protein oxidation compared to animals that remained in CT. We observed that diet (P = 0.02) and environment (P = 0.01) influenced the expression of the RYR3 gene.
CONCLUSIONS. The highest expression of this gene was observed in the breasts of the animals that consumed the sm diet and underwent heat stress. It was concluded that methionine supplementation in the form of free amino acid and dipeptide had beneficial effects on breast yield as well as characteristics that determine the nutritional quality of meat.
Keywords: Methionine, Dipeptide, Antioxidant, Heat Stress.

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