Abstract Jumbo squid (Dosidicus gigas) muscle hardness has been related to hydroxylysyl-pyridinoline (HP) formation (collagen fibre stabilization) via condensation of oxidized ε-amino groups of lysine and/or hydroxylysine by lysyl oxidase (LOX). Previously published literature has suggested the presence of LOX isoforms in squid muscle. Thus, the objective of the present research was to test the hypothesis that squid LOX isoforms exist in fresh mantle muscle. A semi-pure LOX extract (SPLE) was used to perform an immunoblotting assay using two commercial human-LOX antibodies. Furthermore, SPLE (specific activity of 20 mU/mg of protein) was tested in vitro for possible HP formation using several collagenous materials. Immunoblotting assay confirmed the presence of squid LOX at 32 kDa and its isoforms at 34 kDa and 24 kDa. Although LOX oxidized ε-amino groups on collagenous materials, no HP formation was detected. However, the latter could promote interesting collagen functional modifications.

ABSTRACT Nowadays agriculture is facing constantly challenges to produce more and better food for a growing population under a changing climate scenery. To afford this demand, agricultural practices must innovate in new methods for crop production, nutrition management, and plant health. In addition, the development of new compounds or biological agents able to improve plant yield (regulating plant physiology, metabolism, crop performance), and agro-product quality, are also necessary. In the last decade, agents with these characteristics have been proposed for a sustainable agriculture. These agents, defined as biostimulants, have showed to improve plant nutrition, quality, yield and abiotic tolerance in different agricultural crops. In particular, the use of protein hydrolysates as biostimulants offers promising results to reduce the use of agrochemicals and improve productivity parameters in a variety of cultivars, in agree with the modern agricultural production challenges. The present review is focused in the use of protein hydrolysates as plant biostimulants, describing typical and potential agro industrial by-products as sources substrates for protein-based biostimulants formulation, and commercial or experimental proteolytic enzymes used for hydrolysate production. Moreover, critical aspects during protein biostimulants manufacture, functional profiling and its applications are discussed. Finally, recent advances for the evaluation of protein hydrolysates on plant physiology and metabolism under experimental and commercial scale are also documented. Concluding in the necessity to conduct structural studies, in order to identify and produce bioactive peptides with agricultural applications.