Effect of Product Microstructure and Process Parameters on Modified Atmosphere Packaged Bread

Abstract

The objective of this study was to examine bread microstructure, oxygen diffusion properties, and gas exchange between bread and headspace after packaging in modified atmosphere (MA). Breads were produced at laboratory scale, and industrially produced breads were included as a reference. X-ray microtomography was applied to characterize the microstructure of the bread samples. For each sample type, oxygen diffusivity was calculated based on microstructural parameters. The samples for gas analyses were packaged under MA using vacuum compensation, using two vacuum strengths during the air evacuation step. The total porosity of all laboratory samples was above 75%, except for the side and bottom crusts which had a lower porosity (<70%). The porosities of the crumb and the side crust of the commercial bread were 80 and 76%, respectively. The connectivity density of the crumbs of the laboratory and commercial breads was 8 and 10 mm−3, respectively. The crust showed a larger resistance to oxygen diffusion than the crumb, but for both bread regions, the diffusivity was maximally ten times smaller than that of oxygen in air. When considering all data obtained from the gas analysis in the headspace immediately after packaging, oxygen levels of 0.1 ± 0.1% for strong vacuum and 3.8 ± 2.9% for weak vacuum were obtained, which differed significantly (p < 0.05). The results of the laboratory samples corresponded well to those of industrially baked breads. It was concluded that vacuum strength during packaging determines gas transport in bread after packaging.