مشخصات پژوهش

Background: Alkylpyrazines (APs) are a class of the principal cocoa aromatic compounds which are produced by non-enzymatic browning reactions between amino acids and reducing sugars via thermal treatment [1]. The pyrazinic ratio which is defined as the ratios between the concentration of some APs on the volatile fraction of chocolate and cocoa are considered as an important parameter for assessment of these products quality [2]. Therefore, it is required to determine APs in cocoa derived products applying a sensitive and selective analytical method. Methods: Considering the high volatility of studied APs, the head space (HS) mode was selected for performing the proposed hollow fiber protected liquid phase microextractio (HFLPME) method [3]. First, 2 cm segments of hollow fiber membrane (HFM) was mounted on a stainless steel wire and was immersed in n-octanol as extracting media for a few seconds. Then, it was placed on the head space of sample solution for 20 min while the sample solution was agitated at 600 rpm. After performing the extraction, the desorption step was conducted by immersing hallow fiber segment in 100 μL methanol and sonication for 5 min. Finally, 1 μL of it was introduced to the GC-FID injection port. Results: Important parameters influencing the HS-HFLPME process including extraction time, extraction temperature, salt content and desorption solvent volume were optimized applying central composite design (CCD). Considering the method validation, developed method linear dynamic ranges were 1- 200 and 5-500 ng mL-1 for various analytes and the limits of detection (LODs) were in the range of 0.3 to 1 ng mL-1. The method precision (RSD %) was evaluated by six replicate experiments and RSD % values were obtained in the range of 0.8 to 8.2 % for the distilled water (100 ng mL 1). The developed method was used successfully for measurement of AP compounds in cocoa and chocolate-milk samples and the relative recovery percentages (RR%) in the range of 71.7