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Effect of an Edible Pectin Coating and Blanching Pretreatments on the Air-Drying Kinetics of Pumpkin (Cucurbita moschata)

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Abstract

With the aim of making food drying processing data and their evaluation available, this work entails evaluating the air-drying kinetics of fresh pumpkin slices and those pre-treated by applying an edible pectin coating or blanching. The drying kinetics of the fresh, blanched, and pectin-coated pumpkin slices were evaluated at 60 and 70 °C with air velocities of 0.85 and 1.70 m∙s−1. The effects of the pre-treatments and drying parameters on moisture diffusivity were investigated. Under the drying conditions studied, a constant-rate period was found and the falling-rate period was described by the diffusion equation. In order to take shrinkage into account, shrinkage coefficients were incorporated in an approximate way, using the analytical solution of Fick’s equation. The highest constant drying rate values were obtained for the blanched samples, followed by the coated samples and finally the fresh samples. Constant drying rates demonstrated that this period did not significantly influence the estimate of the effective diffusion coefficients. It was shown that the water diffusivity of the coating was high, but only slightly increased the drying time, thus not affecting drying efficiency. Conversely, blanching promoted more water transfer and enhanced drying efficiency. It was concluded that coating and blanching at the temperatures and velocities studied were promising for use as pre-treatments in the drying of pumpkins.

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Abbreviations

A :

Surface area (m2)

α :

Fitting constant (dimensionless)

D eff :

Effective diffusion coefficients of water (m2⋅s−1)

Bi M :

Mass transfer Biot number (dimensionless)

e :

Thickness (m)

k :

Drying rate constant (s−1) (Eq. 10 and 12) and (sn) (Eq. 11)

k G :

Mass transfer coefficient (kg water⋅m−2⋅s−1⋅Pa−1)

m s :

Dry sample mass (kg)

n :

Number of terms of the series (Eq. 6); fitting constant (dimensionless) (Eq. 11); and number of observations (Eq. 13);

N c :

Constant flow of evaporated water (kg water⋅m−2⋅s−1)

P :

Mean percent error (%)

R 2 :

Correlation coefficient (dimensionless)

T :

Temperature (°C)

t :

Time (s)

V :

Volume (m3)

v:

Air velocity (m⋅s−1)

w 0 :

Water content, w.b. (kg water⋅kg−1 wet matter)

X :

Fractional or residual moisture, dry basis (dimensionless)

X :

Water content, d.b. (kg water⋅kg−1 dry solids)

X c :

Critical water content (kg water⋅kg−1 dry solids)

\( \overline{X}(t) \) :

Mean fraction of the water mass, d.b. (kg water⋅kg−1dry solids)

y :

Experimental or calculated value

γ n :

Roots of the transcendent equation tg(γ) = 1/γBi M

κ :

Equilibrium relation at interface between the air and the sample (kg water⋅kg−1 dry solids⋅Pa−1)

ρ S :

Solids concentration (kg dry solids⋅m−3)

0:

Initial state

c:

Critical

cal:

Calculated

d.b.:

Dry weight basis

eq:

Equilibrium

exp:

Experimental

w.b.:

Wet weight basis

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Acknowledgments

The authors are grateful to Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for their financial support (Process 07/07586-0) and for the studentship (Process 04/15550-7), and to Danisco Textural Ingredients- Brazil for donating the pectin.

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Correspondence to Maria Aparecida Mauro.

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Molina Filho, L., Frascareli, E.C. & Mauro, M.A. Effect of an Edible Pectin Coating and Blanching Pretreatments on the Air-Drying Kinetics of Pumpkin (Cucurbita moschata). Food Bioprocess Technol 9, 859–871 (2016). https://doi.org/10.1007/s11947-016-1674-5

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