An alternative approach to control the oxygen permeation across single-dose coffee capsules

• A water-based oxygen barrier hybrid coating for coffee capsules is here presented.
• Coatings of approximately 7 μm were sprayed on flame-treated polypropylene capsules.
• Coating deposition allowed decreasing the oxygen permeability of ∼35 times.
• The barrier performance was also assessed on filled capsules and at high RH.
• This approach can represent an alternative design of the packaging for coffee capsules.

The objective of this study was to investigate the potential of a hybrid coating made of pullulan and a silicon-dioxide precursor to act as an oxygen barrier on polypropylene (PP) capsules used for single-dose ground coffee. PP capsules were first treated by an oxidizing flame to allow better adhesion of the water-based coating solution. The barrier performance of the capsules (uncoated and coated) was assessed by a non-invasive approach based on fluorescence quenching. The deposition of the coating (approximately 7.0 μm thick) led to a dramatic decrease in the oxygen permeation across empty capsules at 40 °C and 25% RH (uncoated capsules: 496.91 mL [package 24 h atm]−1; coated capsules: 14.01 mL [package 24 h atm]−1). In the presence of coffee inside the capsules, the barrier performance was even improved (pack permeability 1.87 mL [package 24 h atm]−1), which was ascribed to the residual oxygen inside the capsules at the beginning of the analysis. At 66% RH, the hybrid coating, while still acting as a good barrier, partially lost its performance due to the simultaneous swelling of the polymer matrix and the presence of fractures on the coating surface. The approach presented in this work can present opportunities for an alternative design of the packaging intended for coffee capsules, with a potential advantage also from an environmental perspective represented by the upstream reduction in the use of plastics.

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