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Bovi, G. G., Rux, G., Caleb, O. J., Herppich, W. B., Linke, M., Rauh, C., & Mahajan, P. V. (2018).
Measurement and modelling of transpiration losses in packaged and unpackaged strawberries. Biosystems
Engineering, 174, 1–9. https://doi.org/10.1016/j.biosystemseng.2018.06.012
Graziele G. Bovi, Guido Rux, Oluwafemi J. Caleb, Werner B. Herppich,
Manfred Linke, Cornelia Rauh, Pramod V. Mahajan
Measurement and modelling of
transpiration losses in packaged and
unpacka
g
ed strawberries
Accepted manuscript (Postprint)Journal article |
Measurement and modelling of transpiration losses in packaged and
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unpackaged strawberries
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In: Biosystems Engineering 174, 1-9.
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Cite as: Bovi, G.G., Rux, G., Caleb, O.J., Herppich, W.B., Linke, M., Rauh, C., & Mahajan,
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P.V., (2018). Measurement and modelling of transpiration losses in packaged and unpackaged
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strawberries. Biosystems Engineering, 174, 1-9.
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doi: https://doi.org/10.1016/j.biosystemseng.2018.06.012
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Measurement and modelling of transpiration losses in packaged and unpackaged
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strawberries
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Graziele G. Bovia, b,*, Guido Rux a, Oluwafemi J. Caleba,c, Werner B. Herppicha, Manfred Linkea,
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Cornelia Rauhb, Pramod V. Mahajana
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a Department of Horticultural Engineering, Leibniz Institute for Agricultural Engineering and Bioeconomy
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(ATB), Potsdam, Germany
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b Department of Food Biotechnology and Food Process Engineering, Technical University of Berlin, Germany
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c Division of Post-harvest and Agro-processing Technologies, Agricultural Research Council (ARC) Infruitec-
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Nietvoorbij, Stellenbosch 7599, South Africa
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*Corresponding author: Phone: +49(0)3315699628;
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E-mail: gbovi@atb-potsdam.de (Graziele G. Bovi); pmahajan@atb-potsdam.de (Pramod V. Mahajan)
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Abstract
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Transpiration and respiration are physiological processes well-known as major sources of
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fresh produce mass loss. Besides causing impairment of external quality, it is associated with
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economic loss since it inevitably decreases saleable weight. To prevent postharvest mass
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losses, by improved modified atmosphere and humidity packaging, comprehensive knowledge
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on the mechanistic basis of both processes and their interactions is essential. The objective of
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this study was to evaluate the contribution of these processes on mass loss of packaged and
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unpackaged strawberries. Experiments on a single strawberry were performed at 4, 12 and
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20°C; and 76, 86, 96 and 100% RH. Mass loss was also investigated as a function of number
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of strawberries and package volume at 12°C. A combined model based on Arrhenius equation
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and Fick´s first law of diffusion for an unpackaged single strawberry and a model based on
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degree of filling was developed and validated with packaged strawberries. These models have
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potential application towards the selection of optimal moisture control strategies for
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strawberries.
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Keywords: Modified atmosphere and humidity packaging, Water loss, Strawberry,
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Transpiration, Degree of filling (DOF)
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Nomenclature
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DOF Degree of filling
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MAP Modified atmosphere packaging
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MAHP Modified atmosphere and humidity packaging
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RH Relative humidity (%)
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TR Transpiration rate
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RR Respiration rate
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VPD Water vapour pressure deficit
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TRm Transpiration rate on mass basis (g kg-1 h-1)
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mi Initial mass of the product (g)
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mt Product mass (g) at a determined time (t) in hours (h)
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Ps Saturation vapour pressure (kPa)
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Pa Actual vapour pressure (kPa)
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T Surrounding temperature (°C)
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BOPP Bi-axially oriented polypropylene
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Ki Mass transfer coefficient
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awi Water activity of the commodity
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aw Water activity of the storage air
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a Model constant coefficient
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Msub Mass loss due to substrate
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TMLR Total mass loss rate
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Vproduct Product´s volume (mL)
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Vpackage Package´s volume (mL)
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1. Introduction
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Modified atmosphere packaging (MAP) systems have been extensively used to reduce
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physiological activity of fresh produce by modifying in-package gas composition as well as to
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reduce mass loss by maintaining high in-package air humidity (Caleb, Mahajan, Al-Said, &
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Opara, 2013a). Most of the packaging materials used for MAP have low water vapour
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permeability, and, therefore, the water vapour released by the product due to transpiration
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remains trapped inside the package, often leading to undesirable condensation (Bovi, Caleb,
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Linke, Rauh, & Mahajan, 2016). Thus, in order to lessen in-package water vapour
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condensation it is essential to shift the system design from MAP to modified atmosphere and
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humidity packaging (MAHP). The main challenge of MAHP is to reduce condensation while
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still maintaining produce water loss as low as possible (Rodov, Ben-Yehoshua, Aharoni, &
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Cohen, 2010). The design based on MAHP not only takes into account the gas composition
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but also the in-package air humidity and moisture control strategies to maintain desirable
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relative humidity (RH) and thus reduce condensation (Bovi & Mahajan, 2017).
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In order to design appropriate MAHP it is essential to understand how much water is released
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by the product. Water loss in fresh produce is commonly measured by quantifying the amount
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or the mass of water lost per unit of time, the transpiration rate (TR). Many models based on
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Fick´s first law of diffusion have been proposed to calculate the TR of a wide range of
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horticulture products such as strawberry (Sousa-Gallagher et al., 2013), pomegranate arils
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(Caleb, Mahajan, Al-Said, & Opara, 2013b), whole mushroom (Mahajan, Oliveira, &
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Macedo, 2008), tomatoes (Xanthopoulos, Athanasiou, Lentzou, Boudouvis, & Lambrinos,
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2014), and pears (Xanthopoulos, Templalexis, Aleiferis, & Lentzou, 2017). These models are
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efficient and valid for single unpackaged products, but their application in a dynamic system
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to estimate the TR of packaged products have not yet been tested.
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Furthermore, the quantity of mass loss over a given period of time has long been accepted as
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being the TR of fresh produce. This was based on the assumption that mass loss due to the
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oxidative breakdown of organic reserves (substrate loss) and the effects that respiration exerts
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on TR, by generating metabolic heat and by supplying additional water that can be lost in
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transpiration, are negligible (Shirazi & Cameron, 1993; Xanthopoulos et al., 2017). Recent
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studies, however, have pointed out the important role respiration plays on TR of fresh
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produce, under water vapour saturated environments which is normally seen in packaged
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fresh produce (Bovi, Caleb, Herppich, & Mahajan, 2018). For instance, Mahajan et al. (2016)
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developed a model to calculate TR based on respiration rate (RR). The authors calculated this
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effect on TR by multiplying RR with a conversion factor of 8.6 obtained from the respiratory
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heat and adding it to model of TR calculations based on Fick´s first law of diffusion.
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Furthermore, the authors indicated that the heat of respiration increased the surface
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temperature of fresh mushroom above that of the surrounding air, thereby creating a water
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vapour pressure deficit (VPD) that may further drive transpirational water losses. In addition,
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Xanthopoulos et al. (2017) developed a model that analyses the contribution of transpiration
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and respiration on water loss using pears as a model product. Water loss indirectly resulting
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from respiration accounts for 39% of the total water loss as a result of water vapour pressure
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deficit at an air temperature of 20 °C and 95% RH.
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