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Protein hydrolyzates (PHs) are a well-known group of plant biostimulants that are obtained by thermal, chemical, enzymatic or mixed hydrolysis from animal or plant sources. PHs are mainly applied to plants with the aim to improve their nutrition level, stimulate metabolism, and increase resistance to abiotic stress. Chemically, the PHs are a mixture of free amino acids, oligo- and polypeptides. Considering the differences in the source materials and hydrolytic processes used for their production it is not surprising that PHs are a very complex and inhomogeneous category of biostimulants. This is a critical point that should be considered by both manufacturers and potential users of such products. With the aim to identify a putative correlation among PHs physic-chemical properties, the different source materials and the hydrolytic process used for their production, 22 PHs available on the market were analyzed for: (i) total amino acids concentration, (ii) free amino acids concentration, (iii) degree of racemization, (iv) degree of hydrolysis and (v) apparent average molecular size. The obtained results confirmed the inhomogeneity PHs. However, the chosen parameters were able to provide information about the above-mentioned correlation. Total amino acids in particular were useful for the identification of the original source material. The degree of racemization was useful for the identification of the type of hydrolysis used during production (chemical or enzymatic). The degree of hydrolysis and free amino acid concentrations were useful for the identification of the intensity of the hydrolytic process. The average molecular size was useful for the identification of polydispersity of the peptide size. In conclusion, the PHs can be adequately characterized only through a multi-analytical approach.

Transmissible spongiform encephalopathies (TSE) are fatal neurodegenerative disorders caused by prions. Animal TSE include scrapie in sheep and goats, and chronic wasting disease (CWD) in cervids. Effective management of scrapie in many parts of the world, and of CWD in North American deer population is complicated by the persistence of prions in the environment. After shedding from diseased animals, prions persist in soil, withstanding biotic and abiotic degradation. As soil is a complex, multi-component system of both mineral and organic components, it is important to understand which soil compounds may interact with prions and thus contribute to disease transmission. Several studies have investigated the role of different soil minerals in prion adsorption and infectivity; we focused our attention on the interaction of soil organic components, the humic substances (HS), with recombinant prion protein (recPrP) material. We evaluated the kinetics of recPrP adsorption, providing a structural and biochemical characterization of chemical adducts using different experimental approaches. Here we show that HS act as potent anti-prion agents in prion infected neuronal cells and in the amyloid seeding assays: HS adsorb both recPrP and prions, thus sequestering them from the prion replication process. We interpreted our findings as highly relevant from an environmental point of view, as the adsorption of prions in HS may affect their availability and consequently hinder the environmental transmission of prion diseases in ruminants.