Enzymatic hydrolysis of protein-rich biomass waste for the production of biostimulants

Rice and soy are, among others, crops that generate larger 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 products1. 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 horticulture2. 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 the type of enzyme(s), experimental conditions (T, pH) and time of hydrolysis was performed to obtain a soy PH with biostimulant activity. Moreover, soy protein hydrolysate was subjected to ultrafiltration through increasing molecular weight cut-off membranes to get different peptide size fractions. The biostimulant effect of soy PH and its ultrafiltered fractions was evaluated on growth and quality of Lactuca sativa L., both under nutritive stress and no stress conditions.