Biochemical and Microbial Changes during Palm Kernel Meal (PKM) Fermentation
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Fermentation was the first step of bioconversion process of palm kernel meal (PKM). The fermentation was done in close canister to minimize the environmental effect. The study was conducted to investigate total microorganism and biochemical changes during PKM fermentation in a closed canister. Fourty two kg of PKM were mixed with 84 L of water and put in the big drum (height 81 cm; diameter 48 cm). The fermentation height in drum is 80 cm. The sample was taken in the depth of ±40 cm from the surface. At interval 12 hours during 7 days take a sample for microbial analysis, pH, total acid, temperature, fibre, protein content, D-mannose, and volatile organic acid. The highest number of aerobic bacteria, 17.2 log10 CFU/g, was found at 24 hours of fermentation PKM. The highest total anaerobic bacteria, 17.3 log10 CFU/g, were found at 72 hours of fermentation PKM. No fungi was found before 96 hours of fermentation and the highest number found, 6.4 log10 CFU/g, was at the end of fermentation PKM. The pH of fermentation decreased after 48 hours from 4.56 to 4.28. The decreased of pH followed by increased total acid concentration from 0.19 to 0.22 mMol/mL after 48 hours of fermentation PKM. After 168 hours of fermentation PKM, the protein content increased 4.79%; while the concentration of hemicellulose, cellulose, and lignin decreased 10.79%, 10.77%, and 51.34%, respectively. The highest mannose concentration, 3.297±0.13 g/L, was found after 36 hours of fermentation PKM. The dominant volatile organic acid is acetic acid with a concentration of 87.89 mMol after 72 hours of fermentation PKM.