Optimizing and predicting degree of hydrolysis of ultrasound assisted sodium hydroxide extraction of protein from tea (Camellia sinensis L.) residue using response surface methodology.

Response surface methodology was employed to investigate the effect of sodium hydroxide concentration (X 1: 0.05-0.15 M), sonication time (X 2: 5-15 min), ultrasonic power (X 3: 150-450 W/L), and solid-liquid ratio (X 4: 20-60 g/L) on the optimization of protein extraction from tea residue. Single frequency countercurrent ultrasound (SFCU) was employed to assist the extraction and subsequent hydrolysis of the protein. Optimal extraction conditions were established and response surfaces were generated using mathematical models. There were positive linear and negative quadratic effects of extraction variables on protein yield. The optimal predicted protein yield of 138.9 mg/g was obtained under the optimum conditions of concentration of 0.13 M, extraction time of 13 min, ultrasonic power of 377 W/L and solid-liquid ratio of 51.5 g/L. A model for the degree of hydrolysis of the extraction process was also obtained which gave a predicted and experimental value of 8.4% and 7.5% respectively. Essential amino acid content of 36.7% was obtained under optimal conditions.