Combining the production of L-lactic acid with the production of feed protein concentrates from alfalfa

The production of L-lactic acid was investigated in combination with the production of protein concentrates in the frame of a green biorefinery for efficient utilization of grasses and legume crops. Alfalfa green juice was the sole substrate utilized for initial lactic acid fermentation with Lactobacillus salivarius, Lactobacillus paracasei or Bacillus coagulans in order to drop the pH and precipitate the plant proteins present in the juice. Afterwards, proteins were separated by microfiltration with 40-42% of protein recovery into protein concentrates, suited for feeding monogastric animals. The (residual) brown juice was investigated as source of nutrients for producing L-lactic acid from glucose or xylose with B. coagulans A107 or B. coagulans A166, respectively. Fermentation of glucose (30, 60, 100 g L^-1) resulted in productivities of 2.8-4.0 g L^-1 h^-1 and yields of 0.85-0.91 g LA per g consumed glucose. Fermentation of xylose (30, 60 g L^-1) resulted productivities of 1.1-2.3 g L^-1 h^-1 and yields of 0.83-0.88 g LA per g consumed xylose. Comparing different brown juices, initial green juice fermentation with B. coagulans is recommended if the brown juice is to be used for producing L-lactic acid. Based on our results, it is possible to combine protein recovery with lactic acid production, and the brown juice proved to be a good nutrient source for L-lactic acid production with high optical purities.