Combined Antimicrobial Effect of Bio-Waste Olive Leaf Extract and Remote Cold Atmospheric Plasma Effluent

• Main Authors: Jose Gustavo De la Ossa, Hani El Kadri, Jorge Gutierrez-Merino, Thomas Wantock, Thomas Harle, Maurizia Seggiani, Serena Danti, Rossella Di Stefano, Eirini Velliou
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: Molecules
• Subjects: polyphenols; olive tree; green technology; antibacterial; food contamination; S. aureus
• Online Access: https://www.mdpi.com/1420-3049/26/7/1890

A novel strategy involving Olive Leaf Extract (OLE) and Cold Atmospheric Plasma (CAP) was developed as a green antimicrobial treatment. Specifically, we reported a preliminary investigation on the combined use of OLE + CAP against three pathogens, chosen to represent medical and food industries (i.e., <i>E. coli</i>,<i> S. aureus </i>and<i> L. </i><i>innocua</i>). The results indicated that a concentration of 100 mg/mL (total polyphenols) in OLE can exert an antimicrobial activity, but still insufficient for a total bacterial inactivation. By using plain OLE, we significantly reduced the growth of Gram positive<i> S. aureus </i>and<i> L. </i><i>innocua</i>, but not Gram-negative <i>E. coli</i>. Instead, we demonstrated a remarkable decontamination effect of OLE + CAP in <i>E. coli</i>, <i>S. aureus</i> and <i>L. </i><i>innocua</i> samples after 6 h. This effect was optimally maintained up to 24 h in <i>S. aureus</i> strain. <i>E. coli</i> and <i>L. </i><i>innocua</i> grew again in 24 h. In the latter strain, OLE alone was most effective to significantly reduce bacterial growth. By further adjusting the parameters of OLE + CAP technology, e.g., OLE amount and CAP exposure, it could be possible to prolong the initial powerful decontamination over a longer time. Since OLE derives from a bio-waste and CAP is a non-thermal technology based on ionized air, we propose OLE + CAP as a potential green platform for bacterial decontamination. As a combination, OLE and CAP can lead to better antimicrobial activity than individually and may replace or complement conventional thermal procedures in food and biomedical industries.