Optimised pu-erh tea infusion by experimental design and response surface methodology

Abstract

Apart from the green and black tea consumption, post-fermented Pu-erh specialties are increasingly present even on emerging markets as the one in Romania. Despite simplicity, infusion preparation should be conducted so that polyphenols content reaches its peak, and toxic elements (heavy metals, nitrates) are eliminated or limited to their maximum admitted levels for foodstuff. The study was carried out based on a central composite design, infusion composition being used for proposing regression models representing the response surface generated by the measured parameters as function of working conditions. The analyzed factors were contact time, temperature, and stirring rate. Multi-objective optimization signaled series of operational parameters values yielding maximum polyphenols, at minimum cadmium and nitrate contents in Pu-erh tea infusions. Typically, infusions prepared at 82 - 83°C, using 6 min contact time, and 170 rpm contain 8.9 % polyphenols, while cadmium reaches 3.98 µg/mL, and nitrate 0.35 mg/mL.