Enzymatic Hydrolysis of Protein-rich biomass waste for the production of biostimulants

Rice and soybeans are among the crops that generate the largest amounts of protein-rich waste, e.g. the protein content of rice bran and soy meal are 13-19% and 44-49%, respectively. Thus, they have high potential to be used as starting materials to produce value-added products.1 To this aim, proteins contained in these agri-food waste must be extracted and separated from the other constituents of biomass, and then hydrolyzed. Enzymatic hydrolysis is an easily scalable, green and cost-efficient strategy which involves the use of proteases, eventually in combination with carbohydrases, to produce mixtures of peptides known as protein hydrolysates (PH), for which a number of applications have been reported. Among them, PH can be used as biostimulans in horticulture.2 Studies show benefits of biostimulants on growth, yield, product quality, resource use efficiency and tolerance to environmental and chemical soil stresses of several horticultural crops3,4. In this work an in-depth investigation of different commercially available enzymatic formulations, experimental conditions (T, pH) and time of hydrolysis was performed to obtain soy PHs with biostimulant activity. A scale-up of the enzymatic reaction was also performed, using a 15L reactor. Five different prototypes of soy PHs were prepared, characterized by elemental analysis and subjected to ultrafiltration through increasing molecular weight cut-off membranes to get different peptide size fractions. Moreover, total and free amino acids in soy PHs were determined with RP-HPLC. Moreover, the biostimulant effect of soy PHs was evaluated on growth and quality of Lactuca sativa L. var. longifolia, both under nutritive stress and no stress conditions.