Animal-Derived Hydrolyzed Protein and Its Biostimulant Effects

Animal-derived hydrolyzed protein has a long history of usage as plant growth enhancer and biostimulant. Worldwide, hydrolyzed protein products represent the third biostimulant category by market size after seaweed extracts and humic substances. Hydrolyzed protein can be produced from either animal by-products, and nonanimal raw materials and by-products (e.g., plants, bacteria, fungi). Indeed, hydrolyzed protein derived from animal by-products was the first discovered and commercialized, actively contributing to the birth of the term and concept of “biostimulant.” The first part of this chapter will provide an overview of the regulatory status of hydrolyzed protein, starting with a general excursus on the different regulatory frameworks outside EU. Then the recent approval of fertilizer regulation CE 1009/2019 (that comprises for the first time the biostimulants, and thus hydrolyzed protein) will be taken into consideration, together with other important regulations (EC 1069/2009 and EC 142/2011), that contain the definition of hydrolyzed protein, the raw materials from which it can be produced, and their transformation methods. Afterward, a detailed description of the most used production methods, focusing mainly on chemical hydrolysis and enzymatic hydrolysis, will be provided. A paragraph that describes the protein chemistry of both the raw materials and the hydrolyzed protein, and an excursus on the main analytical methods used for its characterization, will be included. The second part of the chapter will analyze hydrolyzed protein effects on plants. The effects on whole plant level will be grouped in major categories, according to the claims cited in the biostimulant definition included in fertilizer regulation CE 1009/2019 (i.e., nutrient use efficiency, tolerance to abiotic stress, quality traits, availability of confined nutrients in soil or rhizosphere). The final paragraph will give an overview of the state-of-the-art of scientific knowledge on the action mechanisms of these products.