Abstract
The aim of this study was to produce a valuable protein hydrolysate from palm kernel cake (PKC) for the development of natural antioxidants. Extracted PKC protein was hydrolyzed using different proteases (alcalase, chymotrypsin, papain, pepsin, trypsin, flavourzyme, and bromelain). Subsequently, antioxidant activity and degree of hydrolysis (DH) of each hydrolysate were evaluated using DPPH• radical scavenging activity and O-phthaldialdehyde spectrophotometric assay, respectively. The results revealed a strong correlation between DH and radical scavenging activity of the hydrolysates, where among these, protein hydrolysates produced by papain after 38 h hydrolysis exhibited the highest DH (91 ± 0.1%) and DPPH• radical scavenging activity (73.5 ± 0.25%) compared to the other hydrolysates. In addition, fractionation of the most effective (potent) hydrolysate by reverse phase high performance liquid chromatography indicated a direct association between hydrophobicity and radical scavenging activity of the hydrolysates. Isoelectric focusing tests also revealed that protein hydrolysates with basic and neutral isoelectric point (pI) have the highest radical scavenging activity, although few fractions in the acidic range also exhibited good antioxidant potential.
Highlights
Palm kernel cake (PKC), a main by-product of the palm oil extraction process, due to its poor utility, is mostly used for animal feed
In Malaysia, PKC is produced in large quantities as a result of oil extraction from oil palm
Enzymatic hydrolysis is one of the possible ways to improve the value of PKC by adding useful functional properties and bioactivities, such as antioxidant function
Summary
Palm kernel cake (PKC), a main by-product of the palm oil extraction process, due to its poor utility, is mostly used for animal feed. It can be explored as a potential source of valuable components, especially the plant protein (the content ranging between 15–17%), for human nutrition. In Malaysia, PKC is produced in large quantities (around 2.2 million tons/annum) as a result of oil extraction from oil palm. This amount is significant enough to consider PKC as a bioresource of valuable components and raw materials, such as cellulose, hemicellulose, protein and lignin for several industries. Enzymatic hydrolysis is one of the possible ways to improve the value of PKC by adding useful functional properties and bioactivities, such as antioxidant function
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