A quality by design approach considers both the critical product characteristics and process variables in order to design for optimum packaging. Mathematical modelling can be used to describe the effect of process variables (e.g. environmental conditions) on product characteristics and predict quality and shelf-life. The aim of this study was to i) determine the water-vapour-transmission-rate (WVTR) of different packaging materials, and ii) develop and validate a predictive model for the shelf-life of packed granola breakfast cereal using accelerated storage conditions. The WVTR for each film was measured according to an experimental design (32) with 2 factors (temperature and relative humidity) at 3 levels (10, 30, 40°C; 32-33, 75-76, 89-96%). Granola breakfast cereal was packed using 3 commercial biodegradable materials (NK, NM, N913), biaxial-oriented-polypropylene (BOPP), commercial-packing-material (control) and stored using accelerated conditions (38°C and 90%RH). Samples were assessed for moisture content (critical quality parameter), at regular intervals throughout 82 days of storage. The WVTR of BOPP and N913 films were not significantly affected by RH, whereas temperature had a significant effect on all types of materials studied; an Arrhenius relationship was found to describe the dependency of WVTR on temperature. A global model considering the dependency of temperature and RH was developed and was found to fit the experimental data well. Moisture uptake for packaged granola was found to be significantly affected by both storage time and packaging material. The BOPP film resulted in the lowest moisture gain for the granola, followed by the biodegradable film N913. The predicted shelf life for granola under accelerated conditions ranged from 13-2 days depending on the packaging film, and these results were in agreement with those obtained experimentally. The predicted shelf life for granola under normal storage conditions ranged from 283, 90, 33, 228 days in BOPP, NK, NM, N913 pouches, respectively.
Keywords: quality by design, mathematical modelling, packaging, shelf life, water vapour transmission rate