Characterization, antioxidant, ACE inhibition and toxicity evaluations of palm kernel cake-derived Alcalase® hydrolysate

Abstract Palm (Elaeis guineensis Jacquin) kernel cake protein (PKCP) was extracted and hydrolyzed using Alcalase® 2.4L to obtain hydrolysate (PKCPH), then fractionated using size exclusion chromatography. PKCPH consisted of predominantly fraction one (PKCPH1), containing two peptides (4.9 kDa and 6.3 kDa) with functional amide (6.75–7.04 ppm) and amine (1.5–2.0 ppm) groups. PKCP and PKCPH shared similar amino acid profiles. PKCPH1 had moderate amounts of hydrophobic (23.60%) and antioxidant (26.10%) amino acids, with high hydrophobicity index (Ho 79.60), thus exhibiting the highest antioxidant activity in mostly all the antioxidant assays. On the other hand, fraction two, PKCPH2 (58.8 kDa), possessed strong angiotensin converting enzyme (ACE) inhibitory activity (77.29%), but undetectable antioxidant activity. Furthermore, high viability (87–92%) and negligible cytotoxic activity were revealed with the highest dosages of PKCPH (2 mg/mL) and PKCPH1 (1 mg/mL) in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Salmonella reverse mutation (AMES), alkaline comet and micronucleus (MNi) assays. Besides, in vivo acute oral toxicity test on PKCPH using Sprague Dawley albino rats showed negative outcome according to the consistent body and organ weights as well as normal morbidity. In short, PKCPH is safe for potential applications in the formulation of functional food and nutraceutical products with health benefits.