PROTEIN HYDROLYSATES FROM AGRICULTURAL WASTE BIOMASS: ENZYMATIC PREPARATION, BIOLOGICAL ACTIVITIES AND TECHNO-FUNCTIONAL PROPERTIES

In the last decades there has been an increasing research interest in the substitution of non- renewable fossil resources – crude oil, coal and natural gas – by renewable biomass as a sustainable feedstock for the manufacture of chemicals and fuels. However, research on biomass valorization has mainly focused on the conversion of the C-, H-, and O-containing fractions (i.e., carbohydrates, lignin and triglycerides), whereas the nitrogen containing fraction (i.e. proteins) has received only little attention so far. Protein-rich biomass waste is currently abundantly available from the agro-industry and the production of biofuels. Valorization of these protein-rich wastes consists of the extraction of proteins from biomass, followed by their hydrolysis. Protein hydrolysis, i.e. the cleavage of peptide bonds to give peptides of varying size and free amino acids, can be performed by chemical or enzymatic methods. Enzymatic hydrolysis is preferred to chemical one because it can be performed under mild conditions; usually it avoids side reactions and does not decrease the nutritional value of the protein source. Moreover, enzyme-promoted reactions offer both economic and environmental advantages, fitting into the principles and metrics of green chemistry. Partial protein hydrolysis leads to mixtures of peptides known as protein hydrolysates (PH) for which there is a growing interest in many industrial sectors. Indeed, depending on enzyme specificity and the degree of hydrolysis (DH), it is possible to generate hydrolysate products with functional (e.g. solubility, emulsifying and foaming capacity), biological and nutritional properties that are specific and distinct from those of the parent protein. PHs can be used (i) as biostimulants in horticulture due to their capacity to enhance crop quality parameters, nutrient efficiency and abiotic stress tolerance; (ii) as nitrogen fortification agents in specialist beverages; (iii) as pre-digested ingredients for the preparation of formulations designed to provide nutrition to people with special needs (elderly, children and immunodepressed people); (iv) as ingredients in cosmetics and health care products; (v) as flavor enhancers in food industry and many others. Thus, PHs obtained by protein-rich agro-industrial by-products represent a sustainable solution to the problem of waste disposal, making their production interesting from both environmental and economical point of view. Aim of this research work is to design and set up innovative processes for the preparation of high-added value products as the result of both the use of enzyme technology and the valorization of waste/by-products. Waste upgrading by biocatalysis can result in a number of advantages such as the conversion of by-products in new products, the improvement of resource efficiency, the reduction of the environmental impact and the cutting down of product cost. Specifically, this project aims at developing straightforward, greener and cost efficient routes for the preparation of protein hydrolysates by enzymatic hydrolysis using two underutilized agri-food wastes, i.e., rice bran and soybean meal, and commercially available enzymatic formulations, containing both carbohydrases and proteases. Depending on the property which has to be investigated, different hydrolytic protocols have been set up. Specifically, biological properties of a low molecular weight fraction of a rice bran protein hydrolysate, i.e., antioxidant and ACE-inhibitory, have been investigated. Techno-functional properties, i.e., interfacial tension features, O/W emulsion capability and the relative stability over time, of different soy protein hydrolysates have been deeply studied. Particular attention has been given to the evaluation of PH biostimulant activity due to the collaboration with the partner company ILSA S.p.A., which produces biostimulants and biofertilizers. Specifically, different soy protein hydrolysates have been tested on various cultivars of lettuce, both in hydroponic and greenhouse, under normal and stress conditions. In this context, the hydrolytic protocol was also scale-up using a 10L reactor, in view of an industrial application.