The influence of packaging materials on the dissolved oxygen content of probiotic yoghurt

The health benefits of probiotic functional foods have been widely reported. However, manufacturers face great challenge in guaranteeing delivering beneficial numbers of viable probiotic bacteria through to the end of the product shelf life. The oxygen toxicity of some probiotic species has been shown to contribute to reduced viable counts. The packaging system favoured by manufacturers may play a negative role, promoting oxygen uptake in the product. The research detailed herein evaluates the performance of current packaging materials and an alternative, oxygen-barrier material. Commercial stirred-type probiotic yoghurt was evaluated for dissolved oxygen content over a 6 week period from manufacture to expiry date. The results indicate a rising level of dissolved oxygen in the yoghurts over time. The distribution of oxygen throughout the product was also examined by measuring concentrations in two lateral positions, at three different depths. It was found that oxygen was not distributed homogenously, but was in significantly different concentrations (p < 0.05) at most sampling points. At some locations (near packaging weak spots), readings were approaching saturation, hardly an environment suited to the survival of the anaerobic and probiotic Bifidobacterium species. Yoghurt stored in packaging materials with improved gas-barrier properties was also tested, displaying a decrease in dissolved oxygen levels during storage. It was concluded that using packaging materials with greater gas-barrier properties would help remove a hurdle to the viability of the probiotic bacteria within the food. Suggestions for further steps, such as the addition of an oxygen-scavenging technology, are also made. Copyright © 2002 John Wiley & Sons, Ltd.