Lactobacillus plantarum: Effect of a protective biofilm on the surface of olives during storage

Abstract

The aim of the present study was to investigate the effect of Lactobacillus plantarum adhesion to the surface of olives during storage through studying the interaction between the surfaces of the olives and L. plantarum. The results showed that the total number of adherent L. plantarum increased exponentially from 1.2 × 10⁶ to 1.3 × 10⁸ cfu/g. Images obtained using environmental scanning electron microscopy (ESEM) after 4 days of storage revealed that the olive surface was covered with a uniform and compact biofilm constituted of L. plantarum and yeast. Physicochemical analysis of surface of L. plantarum revealed that it was hydrophilic (Giwi > 0 mJ/m²). The surface of the olives also appeared to be hydrophilic (Giwi = 3.28 mJ/m²). The electron-donor characteristics of the surfaces of L. plantarum and olive were γ⁻ = 53.1 mJ/m² and γ⁻ = 28.1 mJ/m², respectively. The formation of a protective biofilm of L. plantarum increased the hydrophilicity (from 3.28 to 46.14 mJ/m²) and the electron-donor capacity (from 28.1 to 67.2 mJ/m²) of the olive surface by 1 day of storage. Analysis of the impact of the biofilm that formed on the surface of the olives during storage showed a reduction in the content of undesirable planktonic microorganisms, such as fungi, which could have occurred due to competition for nutrients and oxygen or modifications in the physicochemical properties of the olives. Thus, coating the surface of olives with a natural material, such as L. plantarum, may be a first step in developing strategies to prevent their microbial colonization.

Keywords
Protective biofilm; L. plantarum; Olive; ESEM; Physicochemical properties