Comparative Antibacterial Activity of Tryptic‐Hydrolyzed Palm Kernel Cake Proteins of Different Degrees of Hydrolysis

Protein from palm kernel cake (PKC), a feed ingredient for ruminants, was extracted, hydrolyzed with trypsin and tested for its antibacterial properties. PKC hydrolysates of different degrees of hydrolysis (DH%, 60–100) were prepared using trypsin. The hydrolysis conditions were suggested by mathematical models obtained using response surface methodology with two‐level factorial design and central composite rotatable design. The PKC hydrolysates of different DH% were compared for their antibacterial properties. PKC hydrolysates with DH% of 80, 90 and 100 showed the greatest antibacterial efficacy against Bacillus cereus, B. coagulans, B. pumilus, B. stearothermophilus, B. subtilis, B. thuringiensis and Listeria monocytogenes compared with PKC hydrolysates of other DH%, with no significant difference among bacteria (P > 0.05). This result suggests that greater antibacterial activity was proportionately related to higher DH%. Remarkably, an antibacterial protein product was successfully prepared from palm kernel cake (PKC), an oil palm milling waste that is commonly used as an animal feed ingredient. This encouraging finding widens the prospects for the usage of PKC and simultaneously provides a new means of income, but, most importantly, can help fulfill the environmental conservation commitment of Malaysia, the leading producer of palm oil. This study suggests that the PKC protein product may be suitable for application in the food or pharmaceutical industry as an antimicrobial agent.