Antioxidant activity of alcalase hydrolysates of Spirulina proteins

Spirulina microalgae are gaining increasing consideration for its pharmaceutical and nutritional (۶۰–۷۰% protein) virtues. Protein can be further processed to produce peptides that have functional and nutritional properties such as antihypertensive, immunomodulatory, antioxidant, hypocholesterolemic, and metal chelating activity.The purpose of this study is to investigate the relevance between antioxidant properties and the degree of hydrolysis (DH)of hydrolysates resulting from the effect of the alcalase enzyme on Spirulina protein at different times and the effect of time on the DH. For this purpose, Spirulina cells were disrupted with ultrasonication, bead milling, and water suspension methods. The resulting cell extract was hydrolyzed with serine proteases like the Alcalase enzyme. The sampling was taken every hour for up to ۶ hours. DH of the samples was measured by the ortho-phthalaldehyde (OPA) method. Antioxidant activities of the hydrolysates were evaluated by assessing ۲,۲-diphenyl-۱-picrylhydrazy (DPPH) and ۲, ۲′-azinobis (۳-ethyl- benzothiazoline-۶-sulphonate) (ABTS) radical scavenging activity. The ultrasonication method was selected for cell wall disruption. Results demonstrate that the highest increase in DH occurred in the first hour of hydrolysis. Then DH increased gradually with a low slope. The highest DH with an enzyme/substrate ratio of ۱% (v/v) was ۳۳.۴۵% after ۶ hours. Maximum DPPH radical scavenging activity occurred precisely at ۱۲۰ minutes (۲۲.۷۱ ± ۱.۱۸ µM TE/mg protein, DH=۲۸.۲۹ ± ۰.۵۸). The scavenging activity of the DPPH radical increased by more than ۲-fold after ۲ hours of hydrolysis. The antioxidant activity of ABTS radicalscavenging increased and reached ۸۶۲.۰۹ ± ۲۲.۲۶ µM TE/mg protein after ۵ hours of hydrolysis (DH%=۳۲.۸۳ ± ۰.۸۷). This research indicates that along with the increase of DH, the ABTS radical scavenging activity also increases. Therefore, hydrolysis produces peptides that can scavenge DPPH and ABTS radicals at certain times. These results can be used to determine both DH and the time it occurs; therefore, the probability creation and isolation of bioactive peptides increase with high antioxidant activities. So, the hydrolysates or peptides derivative from Spirulina can be used as a functional food to improve and even prevent various diseases and disorders.

Keywords:

Spirulina , cell disruption , degree of hydrolysis , Antioxidant activity , Alcalase