Orthodox tea (Camellia sinensis L .) oxidation under the influence of compressed air: Process optimization

Abstract

Oxidation of the hand‐rolled tea leaves (Camellia sinensis) was done by subjecting the leaves to an oxygen‐enriched environment, under the influence of compressed air. Different air pressure (101–303 kPa) and time (0–90 min) combinations were formulated (central composite design) for the experimental runs. A two‐phase analysis was conducted to determine the responses for pre‐drying samples (theaflavin, thearubigins, and total color of the oxidized tea leaves) and post‐drying samples (aroma index, lightness, redness, and yellowness of tea infusion). Oxidation of the rolled tea leaves under an air pressure of 243.51 kPa for 71.15 min was found to be the optimized condition, following response surface methodology. The validatory experiments have been done that provide favorable results with a desirability value of 0.91. Practical applications The findings of the current study could help the tea growers to produce high‐quality orthodox tea with short processing time. The process optimization findings could be instrumental in increasing productivity along with superior tea quality, leading to higher exportability. For the researchers associated with tea processing, this study would give insight into the concept of using compressed air as a potential medium for tea oxidation process.

Development of super‐atmospheric oxidation chamber for orthodox tea processing and its validation through neural network approach

“…(a–c). The change in the TR values at atmospheric oxidation is consistent with previous studies, which also suggested an increasing trend. At an elevated oxygen concentration inside the SOC, the rate of increase in %TR was faster, as observed in Fig.…”

“…5(b). The TF values of oxidized samples in the SOC are fairly close to the reported values 21 obtained from an environmental control chamber, without the aid of a humidifier and air blower. The optimum oxidation duration is decided based on the peak TF value.…”

“…To conduct the tea oxidation, a cast iron chamber with a capacity of 8 L was taken and made airtight using a rubber washer. Because the desired tea quality was observed below an operating air pressure of 303 kPa, the oxidation chamber was designed to withstand a surplus pressure for safety measures. The chamber had additional arrangements for pressure sensing (measuring scale unit in kPa; with a reading limit of 10 kPa), temperature sensing ( measuring scale unit in °C; with a maximum reading limit of 300 °C), control air recharge and discharge valves to regulate the internal environment of the chamber.…”

“…The samples that were drawn were immediately dipped in liquid N 2 to restrict further oxidation. The samples were then cryogenically ground for spectrophotometric analysis as reported by Panda et al Excessively oxidized samples were not included when analyzing the performance of the SOC.…”

“…Concurrently, the optimum oxidation duration is vital because excessive or limited oxidation may lead to poor quality tea . Recently, extensive work has been carried out on the rapid oxidation of orthox tea, although a mechanization of the process still remains unavailable. In the present study, we aimed to develop a super‐atmospheric oxidation chamber (SOC) for the rapid oxidation of rolled tea leaves during orthodox tea manufacturing.…”