Engineering packaging design accounting for transpiration rate: Model development and validation with strawberries

Integrative mathematical modelling for Modified Atmosphere Packaging (MAP) has been used to determine the gas composition inside a package, but can also be used to determine the packaging needs of fresh produce in terms of permeability to gases and water vapour. Transpiration rate (TR) is an important physiological process that influences relative humidity (RH) and condensation inside the package, and ultimately quality and shelf life. Strawberries are an extremely valuable crop, but they are susceptible to grey mould rot, fungal decay, moisture loss and condensation. Quantification of strawberry transpiration rate TR would be required to estimate the packaging material water vapour transmission rate (WVTR) and therefore optimise engineering packaging design. This study investigated (i) the impact of temperature and RH on strawberry TR, (ii) developed a predictive model for quantifying TR, (iii) integrated transpiration rate model into the engineering packaging design and quantified the target WVTR for packaging of strawberry and (iv) validated packaging design by comparison to commercial packaging. Experiments were conducted following an experimental design, considering two factors at three levels (32), i.e. temperature (5, 10 and 15 °C) and RH (76%, 86% and 96%); TR was recorded during 5 days of storage. The results showed that both RH and temperature had a significant effect on TR. In a given temperature and RH range of study, it varied from 0.24 to 1.16 g/kg h. Mathematical model developed considering the effect of temperature and RH, was further validated at 12 °C and 76% RH, showing very good predictability (R2 > 0.997). The TR model was found to be useful for describing the strawberry packaging requisites and for optimal engineering packaging design for strawberry. The target WVTR for achieving optimal RH of 90% at 5 °C was found to be 162 g/m2 day. Packaging design validation showed that the package designed considering both gas and water vapour requisites of strawberry yielded favourable results for maintaining quality and shelf life of product.