Preparation of antioxidant peptides from tea (Camellia sinensis L.) residue

Albumin, globulin, gliadin, and glutelin were fractionated from tea residue and their antioxidant activities were compared. Upon having a significantly (p < 0.05) higher yield and antioxidant activity, glutelin was further hydrolyzed and the effect of hydrolysis time on the antioxidant activity using DPPH, HRSA, reducing power and FICA were assessed. It was observed that the duration of hydrolysis had a significant effect on the selected antioxidant activities as increase in the hydrolysis duration resulted in an increase in antioxidant activity beyond a certain limit after which there was a decline after continual hydrolysis. Glutelin hydrolysate that exhibited higher activities at the specific hydrolysis duration were fractionated using an ultrafiltration membrane with a molecular weight cut off of 3 kDa. The ultrafiltrated samples were subjected to size exclusion chromatography and four fractions (T-1, T-2, T-3, T-4) were obtained. The antioxidant activities of the fraction with the highest activity was compared to that of the unfiltered fraction (LTk), vitamin C (VC), l-glutathione (GSH) or ethylenediaminetetraacetic acid which served as positive controls. The fraction from the size exclusion chromatography with the highest activity (T-2) had EC50 values significantly (p < 0.05) lower than the positive controls, however, their antioxidant activities were comparable upon increase in concentration.