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Food and Bioprocess Technology

, Volume 2, Issue 2, pp 194–207 | Cite as

Apple Pectic Gel Produced by Dehydration

  • Evangelina Leiva Díaz
  • Leda Giannuzzi
  • Sergio A. Giner
Article

Abstract

A novel, flexible sheet-like food formed by the high methoxyl pectin–sugar–acid gelation during drying of apple puree was investigated to characterize drying-related properties. Product volume was reduced by 68% over the process, and this shrinkage was successfully modeled by assuming the volume reduction equal to the volume of water evaporated. The sorption isotherm at 25 °C was determined, and a new expression for the moisture content, W, as a function of water activity, a w, of the type \(W\,{\text{ = }}\,{\text{C}}_{\text{1}} \,{\text{exp}}\,\left( {{\text{C}}_{\text{2}} \,a_w^{{\text{C}}3} } \right)\) resulted as the most accurate for this J-shaped isotherm. The drying kinetics was studied at 50, 60, and 80 °C in a tray dryer. No constant drying rate period was found, and the drying curve was divided in high- and low-moisture zones. For high moistures, an internal–external mixed control diffusive model coupling mass and heat transfer was applied to obtain a mass transfer Biot number of 2.1. In the low-moisture zone, a diffusive, isothermal drying model for strict internal control was utilized. Diffusivities varied around 1 × 10–9 m2/s for high moistures and were about ten times lower at low moistures, although the activation energies were comparable (15,259 and 16,800 J/mol, respectively). The drying time at 60 °C was 6.67 h. The product scored four points out of five in a sensory evaluation of general acceptability.

Keywords

Fruit leather Hot-air drying Non-isothermal drying 

Nomenclature

A

mass transfer area for evaporation (m2)

aw

water activity, decimal

Ah and Bh

fitting parameters of the Halsey model

Ao and Bo

fitting parameters of the Oswin model

a, b, c, and d

coefficients of the third degree polynomials W = f(t)

Bi

mass transfer Biot number

Cp

specific heat of apples (J kg−1 K−1)

C

constant of the GAB model

C1, C2, C3

parameters of the new sorption model

D

effective diffusion coefficient of water (m2/s)

d

average laminate thickness (m)

D0

Arrhenius preexponential factor (m2/s)

Ea

activation energy (J/mol)

f

multiplier of the preliminary Arrhenius preexponential factor

h

heat transfer coefficient (W/°C m2)

ha

air absolute humidity (kg vapor/kg dry air)

hr

air relative humidity (decimal)

k

constant of the GAB model

Lwd

product heat of desorption (J/kg)

Lw

heat of vaporization of water (J/kg)

m

product mass at any time (kg)

m0

initial product mass (kg)

md

product dry matter (kg)

mwev

mass of water evaporated (kg)

MSS

sum of squares of the deviation

M1n, M2n, M3n and M4n

values of parameters of Eq. 15

r2

coefficient of determination

R

universal gas constant 8.314 J mol−1 K−1

t

time (s)

Ta

air temperature (°C)

T0

product temperature at t = 0 (°C)

T

product temperature (°C)

V

product volume at W (m3)

V0

initial product volume (m3)

Vd

dry matter volume (m3)

Vwev

volume of water evaporated (m3)

W

moisture content (dec., d.b.)

W

product average moisture content (dec., d.b.)

We

equilibrium moisture content (dec., d.b.)

W0

initial moisture content (dec., d.b.)

Wm

monolayer moisture content of the GAB model (dec., d.b.)

Wad

dimensionless moisture content

βn

roots of the equation β n tan β n − Bi = 0

ρ

product density (kg/m3)

ρd

dry matter density (kg/m3)

ρw

liquid water density (kg/m3)

Subscripts

 

hm

high-moisture zone

lm

low-moisture zone

Notes

Acknowledgment

The authors thank Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT), Argentina, for providing funding to Project PICT 2002 09-12196 and to the Comisión de Investigaciones Científicas, CICPBA, CONICET, and Universidad Nacional de La Plata from Argentina for their permanent support.

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Copyright information

© Springer Science + Business Media, LLC 2007

Authors and Affiliations

  • Evangelina Leiva Díaz
    • 1
    • 2
    • 4
  • Leda Giannuzzi
    • 1
    • 4
  • Sergio A. Giner
    • 1
    • 2
    • 3
  1. 1.Centro de Investigación y Desarrollo en Criotecnología de Alimentos (CIDCA)CONICET, Universidad Nacional de La Plata (UNLP)La PlataArgentina
  2. 2.Facultad de IngenieríaUNLPLa PlataArgentina
  3. 3.Comisión de Investigaciones Científicas de la Provincia de Buenos AiresBuenos AiresArgentina
  4. 4.CONICETConsejo Nacional de Investigaciones Científicas y TécnicasBuenos AiresArgentina

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