Solid-state Fermentation of Palm Kernel Cake Using Two Bacillus Strains in Co-culture for Probiotics Production

Abstract

Background and Objectives: Bacillus velezensis and Bacillus subtilis are bacteria commonly used as probiotic microorganisms in animal feed formulations due to their effectiveness in controlling and inhibiting pathogenic microbes. Additionally, they can produce beneficial enzymes that aid animal digestion, including proteases and amylases. Solid-state fermentation (SSF) is a widely adopted process for probiotics production and is also known to enhance the nutritional value of animal feed. However, previous studies have shown that using a single microbial strain in SSF often results in incomplete utilization of nutrients from raw materials at the end of the fermentation process. Therefore, two probiotic strains, B. velezensis and B. subtilis, were selected to enhance the efficiency of nutrient utilization from a raw material. This dual-strain approach is expected to improve probiotics production efficiency from agro-industrial by-products, specifically palm kernel cake, which is a residue from the palm oil production industry.

Methodology: This study employed SSF with B. velezensis and B. subtilis at the ratios of 1:1, 1:2, and 2:1 with palm kernel cake as the fermentation substrate. Fermentation was carried out over a period of 7 days at 37°C. Samples were collected on days 0, 1, 3, 5, and 7 for the analysis. Changes of various parameters were monitored throughout the fermentation period, including total viable count, soluble protein content, protease activity, amylase activity, reducing sugar content, moisture content and pH. The objective was to determine the optimal condition for probiotics production.

Main Results: The results of the study on the optimal ratio for fermenting palm kernel cake with B. velezensis and B. subtilis at ratios of 1:1, 1:2 and 2:1 reveal that the total viable microbial count reached its peak on day 3 for all tested ratios. Similarly, the protease and amylase enzyme activities in the fermented palm kernel cake reached their highest levels on day 3, corresponding with the peak in total viable microbial count. The samples with the ratios of 1:1 and 2:1 exhibited higher protease activity compared to the one with the ratio of 1:2; the 1:1 ratio showed the highest amylase activity among all the treatments.

Conclusions: Utilization of palm kernel cake as a substrate for SSF to produce probiotic microorganisms and to enhance nutritional value was investigated using two probiotic strains, B. velezensis and B. subtilis. A ratio of 1:1 was identified as the optimal condition at the laboratory scale.

Practical Application: The present findings can serve as a basis for scaling up the process to pilot-scale production and can be further developed into a commercial application.