Beyond Conventional Extraction: Cold-Pressed Agro-Industrial By-Products Extracts, Microbial Decontamination by High-Pressure Processing and Antimicrobial Activity Assessment

Cold mechanical extraction represents an attractive alternative to conventional solvent-based extraction methods, as it enables the recovery of functional liquid fractions while generating solid residues with reduced moisture content and improved suitability for further valorization. In this context, the present study aimed to test microbial contamination and antimicrobial activity against Pseudomonas fluorescens and Bacillus spizizenii of cold-pressed extracts obtained from pomegranate peels, grape pomace, olive leaves, and asparagus residues. High hydrostatic pressure processing (HPP) was applied primarily as a non-thermal stabilization treatment to reduce the native microbial contamination of the extracts. Initial microbiological analyses revealed variable levels of bacterial and fungal contamination, with asparagus extract showing the highest microbial load. HPP effectively reduced microbial populations. Antimicrobial activity was assessed through growth kinetics modelling and quantified using a Growth Index (GI). Pomegranate peel extract exhibited the strongest inhibitory effect against both bacterial species, maintaining significant activity even after HPP treatment. Grape pomace extract also showed marked antimicrobial properties, whereas olive leaf and asparagus extracts displayed limited efficacy. The results demonstrated that cold mechanical extraction coupled with HPP stabilization can generate microbiologically safe extracts with preserved antimicrobial functionality, supporting the development of sustainable biorefinery strategies for the valorization of agro-industrial by-products.