2.5. Fatty acid composition
Fatty acid methyl esters (FAMEs) were prepared by alkaline hydrolysis extraction according to the AOAC method (2001). FAMEs were analyzed using a GC-17A Shimadzu Gas chromatograph, equipped with a flame ionization detector. The derivatives were separated on a SP-2560 (biscyanopropil polysiloxane) fused-silica column (100 m long and 0.25 mm internal diameter). The injector and detector temperatures were held at 250 C and 260 C, respectively. Oven temperature was maintained at 240 C. The flow rate of carrier gas (He) was set at 1.0 ml/min. Identification of FAMEs was based on retention times of reference compounds from Sigma-Aldrich Chemical Corporation (St. Louis, MO, USA). Fatty acid compositionwas expressed as percentage of total FAMEs on basis of total mass. The quantification of PUFA, MUFA, and SFA was carried out by using tridecanoic acid (C13:0) as an internal standard. Results are expressed as g/100 g beef burger. All analyses were performed in triplicate.
2.6. Statistical analysis
The means and standard deviations (SD) from three measurements within a batch were obtained from all analytical experiments. Results from the experiments were used as variables and analyzed by using a one-way analysis of variance (ANOVA) from GraphPad software in order to assess the effect of the addition of the antioxidants on the oxidative stability of beef burgers and differences between fatty acid compositions among the samples. The study of the effect of refrigerated storage on the oxidative deterioration of beef burgers was carried out by using a t-studenttest for dependent variables. When statistically significant differences were found, Tukey tests were performed. Statistical significance was set at p 0.05.