Apple Pectic Gel Produced by Dehydration

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 ¼ C 1 exp C 2 a C3 w À Á 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 m 2 /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 (m 2 ) a w water activity, decimal A h and B h fitting parameters of the Halsey model A o and B o 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 C p specific heat of apples (J kg −1 K −1 ) C constant of the GAB model C 1 , C 2 , C 3 parameters of the new sorption model D effective diffusion coefficient of water (m 2 /s) d average laminate thickness (m) D 0 Arrhenius preexponential factor (m 2 /s) E a activation energy (J/mol) f multiplier of the preliminary Arrhenius preexponential factor h heat transfer coefficient (W/°C m 2 ) h a air absolute humidity (kg vapor/kg dry air) h r air relative humidity (decimal) k constant of the GAB model L wd product heat of desorption (J/kg) Food Bioprocess Technol (L w heat of vaporization of water (J/kg) m product mass at any time (kg) m 0 initial product mass (kg) m d product dry matter (kg) m wev mass of water evaporated (kg) MSS sum of squares of the deviation M 1n , M 2n , M 3n and M 4n values of parameters of Eq. 15 r 2 coefficient of determination R universal gas constant 8.314 J mol −1 K −1 t time (s) T a air temperature (°C) T 0 product temperature at t=0 (°C) T product temperature (°C) V product volume at W (m 3 ) V 0 initial product volume (m 3 ) V d dry matter volume (m 3 ) V wev volume of water evaporated (m 3 ) W moisture content (dec., d.b.) W product average moisture content (dec., d.b.) W e equilibrium moisture content (dec., d.b.) W 0 initial moisture content (dec., d.b.) W m monolayer moisture content of the GAB model (dec., d.b.) W ad d...

Effect of Processing Methods on Physical, Chemical, Rheological, and Sensory Properties of Okra (Abelmoschus esculentus)

“…Since reconstitution is a function of time, and hot water is required in the preparation of soup from okra, it is better to reconstitute it in hot water. However, higher temperatures can adversely affect nutritional properties and organoleptic parameters of rehydrated products (Díaz et al 2008). Using a reconstitution ratio of 1:10 (dried okra/water ratio), reconstituted foam-mat-dried okra was noted to have higher swelling capacity than sun-dried and solar-dried okra.…”

Effect of structural modifications on the drying kinetics of foods: changes in volume, surface area and product shape

“…During drying, the apple formulation changes from a fluid-like appearance to a soft paste texture and, finally, to a firm gel. To study the volume variation and the drying kinetic, the initial formulation was placed into acrylic trays (0.18 x 0.138 x 0.013 m), with an initial thickness of 6×10 -3 m, and was dehydrated at 60°C in a forced convection oven, with parallel air flow, to several moisture contents (Leiva Diaz et al, 2009). …”

“…The Heywood shape factors will be evaluated for the fruits studied in this work, so as to assist in the selection of a suitable geometry to represent the fruits. The case of a restructured fruit product experiencing shrinkage during drying will also be presented, as an example that in all cases it is necessary to evaluate the macro-structural changes (Leiva Diaz, Giannuzzi, & Giner, 2009). On the other hand, experimental data predictions of drying kinetics will be compared according to the type of characteristic dimension used for the products: (a) constant, taken before drying; (b) a value for the partially dehydrated product, depending on the particular study of each product; (c) The characteristic dimension will be calculated by a correlation describing volume changes, to be developed in this work with the aim of being general, valid for the three fruits.…”

Comparison of Drying Kinetics for Small Fruits with and without Particle Shrinkage Considerations

“…This treatment is considered necessary here since shrinkage is not symmetrical and non-uniform in most foods. Moreover, according to the bibliography (Arnosti et al 2000;Calli Pacco and Menegalli 2004;Leiva Díaz et al 2009;Mowla 2002, 2003;Moreira et al 2000;Ochoa et al 2002aOchoa et al , b, 2007Sjöholm and Gekas 1995;Raghavan and Venkatachalapathy 1999;Ratti 1994;Ratti and Crapiste 2008;Schultz et al 2007) most published shrinkage data are reported to be independent from drying operating conditions or, at most, dependent on air velocity or drying method (Martynenko 2008). On the contrary, evidence suggests that shape changes with velocity and drying method, notably drying rate (Panyawong and Devahastin 2007).…”