Palm Kernel Cake- A Potential Natural Source of Protein, Hydrolysates, and Bioactive Peptides

Palm kernel cake (PKC) is a by-product of the oil palm industry that is widely used as feed for cattle and poultry. It contains several nutrients, such as vitamins and minerals, and is approximately 20% crude protein. The annual demand for protein is expected to grow by around 30% as a result of the increase in the global population; therefore, seeking inexpensive and novel protein sources to develop nutritious and functional food products and ingredients with higher biological activities is crucial. This review summarizes the research on the utilization of PKC as an under-utilized and inexpensive source of proteins for applications in different food products, exploring their effect on human health and food quality. PKC proteins can be effectively extracted using alkaline solubilization (pH 9–11) or enzyme-assisted methods, yielding 60%–70% of available protein. These proteins can be enzymatically hydrolyzed using proteases such as papain, alcalase, and trypsin to generate bioactive peptides with potent antioxidant (DPPH radical scavenging > 70%), antihypertensive (ACE inhibition of 70%–75%), and antimicrobial activities. Key PKC-derived peptides, including AWFS, WAF, and LPWRPATNVF, demonstrate high bioactivity even at low concentrations (IC₅₀ values 0.08–0.35 mg/mL). The production and fractionation of PKC bioactive peptides through different procedures and techniques and their bioactivities on the human body and antioxidant potentials are also reviewed. As an abundant and inexpensive protein source, PKC could be used to produce protein hydrolysates and bioactive peptides commercially. However, further research on PKC, especially on protein extraction and isolation, is needed to confirm its commercialization and use as a reliable and sustainable protein source to produce various functional food and non-food products.