Effect of different drying processes on the chemical, sensory, and volatile characteristic of instant green tea

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ABSTRACT This study compared three drying methods for instant green tea (IGT): conventional spray-drying (CSD, inlet air temperature 170 °C, outlet air temperature 78 °C), freeze-drying (FD, initial temperature -45°C), and electrostatic spray-drying (ESD, inlet air temperature 70 °C, outlet air temperature 38–42 °C).Statistical analysis revealed significant differences in IGT quality among the drying methods. Freeze-dried IGT demonstrated the lowest moisture content (3.6±0.11%) and water activity (0.23±0.01), with Electrostatic spray-dried IGT showing comparable results, Conventionally spray-dried IGT exhibited significantly higher moisture content. Freeze-dried IGT achieved the highest yield (42±0.32%) and solubility, while Electrostatic spray-dried IGT (38±0.27%) outperforming Conventionally spray-dried IGT (35±0.43%). Sensory evaluations indicated that Freeze-dried and Electrostatic spray-dried IGT exhibited more balanced flavors, Electrostatic spray drying IGT scored closely to Freeze-dried IGT in astringency (4.92±0.10 vs 5.77±0.15) and bitterness (4.23±0.06 vs 4.74±0.15), with both significantly outperforming Conventionally spray-dried IGT (p<0.05). Chemical analysis showed Freeze-dried IGT retained the highest levels of caffeine (7.74±0.01 mg/g), amino acids (231.99±0.36 mg/g), gallic acid (1.55±0.52 mg/g), and total polyphenols (301.3±8.16 mg/g), followed by Electrostatic spray-dried IGT. Conventionally spray-dried IGT showed significantly lower concentrations. Antioxidant capacity followed the order Freeze-dried IGT > Electrostatic spray-dried IGT > Conventionally spray-dried IGT, consistent with polyphenol content. Volatile compound analysis identified 103 aroma compounds in Freeze-dried IGT, 66 in Electrostatic spray-dried IGT, and 32 in Conventionally spray-dried IGT. Odor activity value (OAV) analysis determined 13 key aroma compounds, including linalool, β-damascenone, geraniol, and decanal, as well as benzeneacetaldehyde, nonanal, and (E,E)-2,4-heptadienal, critical contributors to the chestnut-like aroma. The total concentration of these compounds showed a trend of Freeze-dried IGT > Electrostatic spray-dried IGT > Conventionally spray-dried IGT, aligning with sensory evaluation results for chestnut-like aroma intensity. Overall, the three drying methods significantly impacted IGT quality. Research shows that electrostatic spray drying is more suitable than conventional spray drying for producing high quality and high fidelity IGT, when using high-quality tea raw materials, with product quality close to that of freeze dried IGT. Thus, electrostatic spray drying offers a novel method for manufacturing high quality instant green tea.

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