Optimized the Fermentation Process of Eggshell and Soybean Dregs to Produce High Calcium Feed by Response Surface Methodology

Discarded eggshells and wet soybean dregs are rich sources of calcium and nitrogen. This study aimed to establish a novel optimized method for the utilization of agricultural wastes. Eggshells and soybean dregs were the primary raw materials used in this study. Bacillus subtilis, Lactobacillus plantarum, and Enterococcus faecalis were the probiotic strains selected for mixed fermentation. Harman’s single-factor test based on the assessment of calcium lactate content in the fermented forage was used to screen the following process parameters: Ratio of soybean dregs to eggshells, solid to water ratio, addition of glucose, inoculation amount, ratio of probiotic strains, fermentation temperature and duration. Optimum fermentation conditions were determined using response surface methodology. The results revealed that the conditions required for optimum fermentation were as follows: Soybean dregs to eggshells ratio of 90:10, solid to water ratio of 1:2.5, addition of 15.6% glucose, inoculation amount of 14.7%, Bacillus subtilis, Lactobacillus plantarum and Enterococcus faecalis in the ratio of 1:1:1 (v/v), and fermentation duration of 6 days at 37 °C. The amount of calcium lactate in the fermented forage was 13.58%. Free amino acid and calcium lactate concentrations in the fermented forage were significantly higher (P<0.05) in comparison to their concentrations in the raw materials. A significant decrease in pH and concentrations of crude fat and soluble protein in the fermented forage was also observed (P<0.05). In conclusion, this study established a novel optimized method for the production of high calcium feed from eggshells and soybean dregs using probiotic fermentation.