DEVELOPMENT OF NATURAL-SOURCE ANTIMICROBIAL SYSTEMS FOR EXTENDING THE SHELF LIFE OF TABLE OLIVES DURING PACKAGING

The OLIVEPACK project aims to develop a new packaging for table olives that ensures microbiological safety under reduced sodium chloride content without chemical preservatives while extending shelf life. To achieve this, sustainable materials and natural bioactive compounds are integrated into functional inserts designed for the gradual release of natural antimicrobial agents during packaging.

Among the compounds evaluated, hydroxytyrosol was selected due to its superior performance. This bioactive phenolic compound, obtained from olive processing wastewater, was chosen for its strong antimicrobial activity, natural origin, and suitability for direct food-contact applications. In addition, naturally occurring aluminosilicate clay halloysite nanotubes were selected as carrier systems due to their tubular morphology, high specific surface area, and intrinsic ability to encapsulate and provide sustained release of active compounds. Hydroxytyrosol-loaded halloysite nanotubes were incorporated into cellulose-based bionanocomposite foams, serving as sustainable active packaging inserts. The renewable and biodegradable cellulose matrix supports the integration of the nanocarriers and the controlled release of hydroxytyrosol, creating a material for active food packaging applications.

Subsequently, this methodology was evaluated to characterize its antimicrobial efficacy both in vitro, using agar-contact assays and bacterial viability measurements, and in packaged table olives through microbial challenge tests against spoilage and foodborne bacteria. The foam effects were fitted using nonlinear regression methods. Hydroxytyrosol-loaded foams exhibited significantly enhanced antibacterial activity in vitro compared with unloaded cellulose foams. Foam-treated samples reduced bacterial populations to below 1 log₁₀ CFU after 48 h, whereas untreated controls remained at approximately 1.3–3.3 log₁₀ CFU, depending on the microorganism. Although the antimicrobial effect varied with the formulation and target microorganism, further optimization is required. In particular, reducing antimicrobial reagents during foam preparation is necessary because their inherent antimicrobial activity masks the specific contribution of hydroxytyrosol, limiting the assessment of its full potential as a natural protective compound.