Enzymatic production of bioactive peptides from sericin recovered from silk industry wastewater

Bioactive peptides were produced from sericin, a by-product from silk industry wastewater, by using Protease P. The optimal hydrolysis conditions (pH of 8.40, temperature of 43.97 degrees C and the enzyme/substrate ratio of 3: 100) were estimated by using response surface methodology with a maximum degree of hydrolysis of 14.43% and the minimum IC50 value for the ferrous ion-chelating activity of 0.128 mg/mL. The freeze-dried sericin hydrolysate (SH), produced by using Protease P and under the above optimal conditions, contained 82% of crude protein, 13% of moisture and 5% of ash. The physiochemical analysis shows that the amino acids with hydroxyl groups (Ser and Thr) of SH accounted for 30% or so, and SH was a mixture of hydrophilic peptides mostly distributed among 250-4000 Da. SH exhibited excellent antioxidant activities in two measurements, including the ferrous ion-chelating activity and the reducing power. Moreover, SH also exhibited a notable tyrosinase-inhibitory effect in a dose-dependent manner. This study firstly showed an effective bioprocess for the production of sericin bioactive peptides, which may be used as valuable ingredients in the food, cosmetic and medicine industries. (C) 2008 Published by Elsevier Ltd.