Proteomic investigation on a food enriched with proteins from dairy by-products

The dairy industry has an important position among the food industries due to the increasing demand for milk-based products [1]. Nonetheless, processing, microbial spoilage, and inadequate handling of such foods could lead to a number of waste and by-products [2]. Due to their high nutritional value, dairy products’ wastage could cause a loss of nutrients that could instead be reused to improve the nutritional value of other foods. Ricotta cheese is a typical Italian dairy product which demand has gradually increased in the last few years due to consumers’ preferences for more natural and healthy foods [3]. Unfortunately, artisanal premium quality of this dairy product is affected by high perishability and, consequently, short shelf-life [4]. Although counted as a by-product, aged ricotta cheese still contains valuable compounds thus deserving to be reused for high-nutritional food production. In this study, a cottage cheese was produced from whole bovine milk enriched with 6-days aged ricotta cheese in the perspective of valorizing this by-product. Milk mixed or not with aged ricotta, along with cottage cheese fortified or not with ricotta, were submitted to proteomic investigation by means of mono-dimensional electrophoresis (SDS-PAGE) and High-Resolution Mass Spectrometry based on Orbitrap technology (LC-HRMS/MS) analyses tailored to verify changes in protein and peptide composition. SDS-PAGE profiles of fortified milk and cottage cheese samples highlighted that the protein pool of the new product was enriched in the whey protein fraction, especially for β -lactoglobulin content. On the other hand, the untargeted LC-HRMS analysis obtained by running the instrument in Full-MS/dd-MS2 acquisition mode followed by bioinformatic investigation, unveiled a significant increase in the content of some bioactive peptides in the cottage cheese enriched with aged ricotta. Specifically, a total of 227 peptides belonging to αS1-, αS2-, β- and k- caseins along with β-lactoglobulin were correctly identified in cottage cheese fortified or not with the aged ricotta, with 14 of these showing bioactivity, such as ACE inhibitor, antioxidative activity or zinc binding. Interestingly, some bioactive peptides derived from β-lactoglobulin, and casein proteins were found with a two- or three-fold increase in the enriched cottage cheese. Our study highlights the real potential to use dairy by-product to produce high-nutritional value foods in the perspective of food waste valorization.