Evaluation of Roasting Effect on Selected Green Tea Volatile Flavor Compound and Pyrazine Content by HS-SPME GC-MS

Abstract

The present study aims at the development and validation of a quali-quantitative headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME GC-MS) method for the analysis of odorants in different Chinese and Japanese green teas. A 65 µm PDMS/DVB fiber was used, and GC-MS was performed on a ZB-5 (30 m × 0.25 mm ID, 0.25 μm film) column. The main odorants in green tea samples were identified and the method was fully validated. Linearity (r2 0.981–0.999), sensitivity (LOQ 0.005–0.04 µg/mL), reproducibility (CV% 3.12–10.37), accuracy (recovery% 79.08–99.17) and matrix effect (ME% −9.5 to +4.5) were determined. Quantitation of 2,4-heptadienal, β-damascenone, β-ionone, linalool, indole, 2-ethyl-6-methyl-pyrazine, 2-ethyl-5-methyl-pyrazine, 2-ethyl-3,6-dimethylpirazine, 2-ethyl-3,5-dimethyl-pyrazine and 2-acetyl-pyrazine was carried out in the presence of isotopically labeled compounds as the internal standards. The proposed method was applied to the comparison of the profile of the volatile flavor compounds (VFCs) of green tea subjected to roasting treatment at three different temperatures (160, 180 and 200 °C for 30 min). In particular, the roasting process was monitored by following the quantitative variations of the selected odorant content, considered as the most important contributory components to the Hojicha or black tea (roasted tea) flavor. A temperature of 160 °C was found to be the best roasting temperature.

Formation of Volatile Heterocyclic Compounds and Open-Chain Amides of Theanine in Model Systems with Glucose, Tea Leaves, and Tea Extract under Tea-Roasting Conditions

“…The roasting procedure is generally applied toward the end of the process and is designed specifically to introduce a “roasty” signature to certain styles of tea leaves. The classic examples include the roasted green tea Hojicha, charcoal-baked Tieguanyin, large leaf yellow tea, and many styles of oolong tea. , Unique sensory profiles can be achieved by artfully manipulating the roasting conditions, such as the temperature, duration, interval, and air movement. The roast method is employed frequently as the quality- and character-determining final touch for tea products.…”

“…It is well-known that, during tea processing, the amino acids and sugars in tea leaves undergo Maillard reactions and produce many aroma impact molecules . Especially, aroma molecules formed under the conditions of tea roasting strongly enhance the roast characteristics of tea leaves . Research activities on Maillard reactions were mostly focused on the proteinogenic amino acids, while the knowledge of theanine reactions is greatly limited regarding the formation of volatile compounds.…”

“…1 Especially, aroma molecules formed under the conditions of tea roasting strongly enhance the roast characteristics of tea leaves. 2 Research activities on Maillard reactions were mostly focused on the proteinogenic amino acids, while the knowledge of theanine reactions is greatly limited regarding the formation of volatile compounds. As the most abundant amino acid in tea leaves, it is of great importance to understand the role of theanine in tea aroma development.…”