Theanine and catechin extraction from green tea waste using water and subcritical water

Tea (Camellia Sinensis), a drink with a pleasant taste and aroma, is widely consumed in Turkey and in the World. Green tea contains bioactive compounds, such as theanine (0.1-2% dry wt), an amino acid that is responsible for the "umami taste" of tea, and catechins (30-42% dry wt), phenolic compounds with antioxidant activity. Therefore tea processing waste, which has no commercial value, can be utilized as a source of catechins and theanine with potential commercial applications in food, dieatary supplement, nutraceutical, and cosmetic industries. In this thesis, water extraction yields of theanine and catechins from green tea processing waste were determined considering the effects of extraction temperature (30-90°C) and time (5-30 min). The potential of using subcritical water (SCW) extraction system for the recovery of theanine and catechins from green tea waste was also evaluated. The effects of extraction temperature (50-110°C), time (5-60 min) and flow rate (2 ml/min and 4 ml/min) of SCW extraction on extration yields were investigated. Theanine and catechin content of the extracts were determined using HPLC-PDA. Maximum extraction yields of theanine (4.21±0.12 mg/g dry wt) and total catechins (74.82±0.48 mg/g dry wt, 76% EGCG) were obtained at 90°C in 30 min and at 80°C in 15 min, respectively, using conventional water extraction. Higher yields (increased by 4%, 3%, and 12%) could be achieved using SCW for theanine, total catechins and EGCG at 90°C in 60 min with 2 ml/min (for theanine), 110°C in 45 min with 4 ml/min (for catechins). SCW extraction curves were constructed for theanine and catechins to investigate the effect of temperature, time, flow rate and degradation/epimerization reactions on extraction yield, recovery and rate. Recovery of theanine and catechins from green tea waste using a sustainable technology offers product development opportunities for various applications in food industry.