Quality control of natural cork stoppers by image analysis and oxygen transmission rate

Abstract

Abstract This work presents the evaluation of the porosity by image analysis, the quantitative analysis of the cell morphology from images obtained by scanning electron microscopy (SEM) and the oxygen transmission rate (OTR) of natural corks of different visual quality grades. Due to the natural variability of cork stoppers, statistically significant differences could not be established in the porosity of the corks according to their commercial quality. However, the determination of the surface porosity coefficient by image analysis in the tangential and axial sections of the corks allowed us to distinguish between high, medium and low quality classes. The cells in the tangential section were shaped between circular and hexagonal, with very regular perimeters regardless of the cork quality. While the cells of the radial and axial sections showed a square and rectangular shape, with more irregular perimeters, mainly in the lowest quality corks and in the axial section. Corks commercially classified as “flower”, “second” and “third” had the lowest OTR values and presented a similar statistical distribution in their cell perimeters in the axial section. While the corks with higher OTR values (superior and fourth qualities) corresponded with those with greater cell perimeters and greater dispersion in their distribution.