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ISHS Acta Horticulturae 1141: III International Conference on Fresh-Cut Produce: Maintaining Quality and Safety

Mathematical model for transpiration rate at 100% humidity for designing modified humidity packaging

Authors:   P. Mahajan, G. Rux, O. Caleb, M. Linke, W. Herppich, M. Geyer
Keywords:   fresh produce, condensation, transpiration, respiration, packaging
DOI:   10.17660/ActaHortic.2016.1141.33
Water vapour saturation is commonly observed in packaged fresh produce. The reason is that moisture evolves from the product, but the packaging material has insufficient water vapour permeability. Under such conditions, even minor temperature fluctuations result in condensation inside the package, causing sliminess, decay, enhanced microbial growth and browning of the product surface. This study investigated the moisture loss behaviour of mushroom, strawberry and tomato under 100% relative humidity (saturated) storage environments at 13C. The mass and surface temperature of each product was measured continuously using an electronic balance and infrared thermometer connected to a data logger. A perforated plastic sphere filled with water-storing polyacrylamide granulates was used as a dummy evaporation sphere. Despite water vapour saturation, mushrooms, strawberries and tomatoes transpired at rates of 712, 122 and 18 mg water kg-1 h-1, respectively. Respiratory heat production led to higher product surface temperature than that of the surrounding air. In turn, this resulted in an outward-directed water vapour gradient. This was confirmed by the absence of mass loss from the evaporation sphere. Interestingly, when mushroom was exposed to lower humidity (65%), there was a rapid increase in mass loss. Consequently, evaporative cooling significantly reduced the surface temperature below the surrounding air temperature. A generalised mathematical model developed an adequately predicted transpiration rate as a function of temperature, relative humidity of storage environment and respiration rate for selected fresh products. Application of the model to design modified humidity packaging was demonstrated for these selected fresh products.

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