Department of Food Science and Technology, Cornell University, Geneva, New York, USA.
J Agric Food Chem. 2009 Sep 23;57(18):8250-7. doi: 10.1021/jf9019695.
We describe an optimized protocol for analysis of the herbaceous smelling 3-alkyl-2-methoxypyrazines (MPs) in whole berries that predicts MPs in resultant red wines. Berries are homogenized by bead-milling with a deuterated standard prior to headspace solid phase microextraction (HS-SPME) and quantification by two-dimensional gas chromatography time-of-flight-mass-spectrometry (GCxGC-TOF-MS). In the case of 3-isopropyl-2-methoxypyrazine (IPMP), GCxGC-TOF-MS successfully resolved interferences that coeluted with the analyte in the first dimension. HS-SPME parameters (pH, queue time, incubation time, extraction time, extraction temperature) were optimized by a statistical experimental design. Good method accuracy was observed (consistent ratio of unlabeled analyte to labeled standard) at 10 min extraction times when 80 degrees C extraction temperatures were employed, although increasing sensitivity was observed for longer extraction times (up to 140 min). Standard addition of 3-isobutyl-2-methoxypyrazine (IBMP) and IPMP into preveraison and harvest ripe berry matrices showed good linearity (r(2) >0.99 in all cases), with limits of detection ranging from 0.6 to 1.8 pg/g. The protocol was validated by comparing IBMP in 16 lots of Cabernet Franc berries (range = undetectable to 18.4 pg/g) to the resulting wines (range = undetectable to 14.5 pg/g). Berry and wine MP content were strongly correlated, (r(2) = 0.97, p < 0.0001). Following correction for CO(2) loss, the observed concentration of IBMP in wines was 67 +/- 13% of the IBMP concentration observed in berries.
我们描述了一种优化的方案，用于分析全浆果中具有草本气味的 3- 烷基 -2- 甲氧基吡嗪（MPs），并预测其在相应红葡萄酒中的含量。在进行顶空固相微萃取（HS-SPME）和二维气相色谱飞行时间质谱（GCxGC-TOF-MS）定量分析之前，将浆果通过珠磨均质化处理，并用氘代标准物进行处理。对于 3-异丙基 -2- 甲氧基吡嗪（IPMP），GCxGC-TOF-MS 成功地分离出与分析物在第一维共洗脱的干扰物。通过统计实验设计优化了 HS-SPME 参数（pH 值、队列时间、孵育时间、提取时间、提取温度）。当采用 80°C 的提取温度并提取 10 分钟时，观察到良好的方法准确性（未标记分析物与标记标准品的比值一致），尽管随着提取时间的延长（最长可达 140 分钟），灵敏度有所提高。在预成熟和收获成熟浆果基质中加入 3-异丁基 -2- 甲氧基吡嗪（IBMP）和 IPMP 的标准添加显示出良好的线性关系（所有情况下 r²>0.99），检测限范围为 0.6 至 1.8 pg/g。通过比较赤霞珠弗朗克（Cabernet Franc）浆果 16 个批次中的 IBMP（范围为无法检测到 18.4 pg/g）与相应葡萄酒（范围为无法检测到 14.5 pg/g），验证了该方案的有效性。浆果和葡萄酒中 MPs 的含量具有很强的相关性，（r²=0.97，p<0.0001）。在对 CO₂ 损失进行校正后，葡萄酒中 IBMP 的观察浓度为浆果中 IBMP 浓度的 67±13%。
