The invention describes a novel composition of matter obtained from the leaves of green plants, which is useful in promoting the growth of beneficial microorganisms. Specifically, that the invention describes a hydrolysate prepared from plant leaf biomass (leaf biomass hydrolysate or ‘LBH’) which dramatically stimulates the growth of beneficial microorganisms. Use of LBH as a fermentation substrate can also stimulate rapid production of organic acids and other organic compounds. LBH can be used as a substrate to promote the fermentation-based production of biobased industrial chemicals or biofuels, LBH can be utilized as a prebiotic to promote the growth of beneficial probiotic organisms, hi addition, LBH may also be useful in stimulating the fermentation-based production of other products, examples of which include preservatives, antibiotics, antigens, vaccines, amino acids, vitamins, recombinant proteins, bioremediation treatments, and immobilized enzymes.