Effects of Humic Acid Dosage and Fermentation Time with Bacillus subtilis on Nutrient Content and Quality of Palm Kernel Cake

This study aims to determine the effects of humic acid dosage and fermentation time with Bacillus subtilis on the nutrient content and quality of Palm Kernel Cake (PKC). A Completely Randomized Design (CRD) with a 3 × 4 factorial pattern and 3 replications was applied. The present experiment considered two major parameters, termed A and B. Factor A represents the humic acid dose in three different compositions, including A1 (100), A2 (200) and A3 (300 ppm), while B refers to the fermentation time, comprising B1 (3), B2 (4), B3 (5) and B4 (6 days). Variables employed were enzyme activities of cellulase, manannase and protease, as well as crude protein content, crude fiber, crude fat, nitrogen retention, crude fiber digestibility and metabolic energy. The variance analysis results showed a significant effect (p<0.05) between factors A and B on cellulase, manannase and protease performances as well as crude protein, crude fiber, crude fat, nitrogen retention and crude fiber digestibility. Each component also observed a substantial effect (p<0.05) on these parameters. In summary, the PKC samples fermented with B. subtilis at 300 ppm humic acid and 6 days fermentation period generated the optimal results, as indicated by the activities of cellulase 17.86, manannase 25.37 and protease 10. 63 U/mL, as well as the percentage composition of crude protein 28.78, crude fiber 13.55, crude fat 0.76, nitrogen retention 68.76 and crude fiber digestibility 57.47%.