Optimizing Fixing and Drying Conditions in Green Tea Processing of Different Tea Varieties From the Eastern Hills of Nepal

Green teas are the sources of bioactive compounds with potential health benefits. This study aims to optimize fixing and drying conditions for Nepalese tea varieties: Gumti (G-t), Takda 383 (T-383), Happy-valley 39 (HV-39), Takda 78 (T-78), and Phubtsering 312 (Pb-312). Pan firing and drying were performed at 100°C, 105°C, 110°C, 115°C, and 120°C to achieve a final moisture content of 10%. The chlorophyll content was used to assess the indicator of green tea quality during the fixing process. The effect of varieties and temperature variation was significant (p < 0.05) for the antioxidant activity, total phenol, caffeine, and flavonoid content. The values of the experimental moisture ratio were calculated and compared, and the best-fitted model was selected based on the statistical parameters. The peroxidase inactivation took longer at 100°C. However, all varieties had higher chlorophyll retention at this temperature. For T-383 and T-78, peroxidase inactivation was at 7 min; for others, it was at 8 min at 100°C. Drying at 100°C for all varieties had more total phenols, flavonoids, and DPPH scavenging activity. Caffeine content was least affected by the drying temperatures. However, there was variability in the values due to varietal and temperature differences. The T-78 drying at 100°C is the best quality among all samples, with a diffusivity of 7.66 × 10⁻⁸ m²s⁻¹, and the Midilli model was the best fit. In conclusion, pan firing at 100°C for 7–8 min, followed by drying at 100°C for 1.17 h, is recommended for green tea processing. This ensures the highest retention of phytochemicals while maintaining desirable quality attributes. Drying conditions for each variety must be tailored to optimize energy efficiency and product quality.