http://paginas.fe.up.pt/~sereno/publ/2004/JFE_ShrinkReview.pdf

Modelling shrinkage during convective drying of food materials: a review

Size, Shape, Volume, and Related Physical Attributes.- Rheological Properties of Foods.- Thermal Properties of Foods.- Electromagnetic Properties.- Water Activity and Sorption Properties of Foods.- Surface Properties of Foods.

Physical properties of foods

Dependable data on bulk density, volumetric shrinkage due to water loss and porosity are needed to model processes such as drying, packaging and storing. Experimental data are presented for all three properties. It is possible to model the water-loss-based bulk shrinkage coefficient to obtain a predictive equation based on composition of the foodstuff. From this, a generalized correlation is obtained which predicts bulk shrinkage coefficient knowing only the initial moisture content of the food. Porosities for the foodstuffs considered can be predicted through suitable correlations, but there is no generalized equation spanning all foods.

Shrinkage, Porosity and Bulk Density of Foodstuffs at Changing Moisture Contents

Effects of drying and grinding in production of fruit and vegetable powders: A review

Shrinkage during drying of foodstuffs

A simple procedure has been implemented to measure porosity of apples as a function of moisture contents. The method has been applied to apples with change in moisture contents by conventional air drying. It is shown that the pores, which for biological reasons are open, i.e. connected to the outside, at the onset of dehydration, remain so until X = 1.5 g/g. As dehydration proceeds the pores are split into two families of pores: externally connected pores and locked-in bores. Both total and open pore porosity can be predicted from experimental correlations. Alternatively, the total porosity can be estimated from data on bulk volume shrinkage and the average composition of the tissue by means of equations presented. The interpretation of experimental data using this approach confirms that there is a significant change in the three-dimensional arrangement of the cellular tissue below X = 1.5 g/g. The two approaches lead to the conclusion that, probably due to cellular collapse, the open structure that characterizes the fresh foodstuff changes into a structure with locked-in pores. This fact may help to explain the slow and difficult re-hydration which characterizes air-dried foodstuffs. This hypothesis will be followed up in future work. The information developed should be of help in qualitative and quantitative modeling of processes involving moisture changes.

Total porosity and open-pore porosity in the drying of fruits

Determination and correlation of heat transfer coefficients in a falling film evaporator

Retention of aroma compounds in basil dried with low pressure superheated steam

Mathematical modeling of moisture evaporation from foodstuffs exposed to subatmospheric pressure superheated steam

It is inferred from experimental data that in drying foodstuffs with superheated steam, the initial drying rate has a direct effect on the rate at which the overall drying takes place. That is, the faster the initial drying rate, the shorter the overall drying time. This criterion is very convenient because at the beginning, water moistens the sample external surface so evaporation does not depend on internal sample characteristics, but only on external convective heat and mass transfer rates. Mass and energy balance equations are solved and the result converted into a general initial drying rate equation, in which all dryer characteristics are grouped into one dimensionless parameter. The initial drying rate equation is mathematically maximized and the optimum working conditions determined. The result shows that initial drying rate always increase with increases of either the superheated steam temperature or velocity, but once these two variables are fixed, there exists at least one “optimum” pr...

M.J. Urbicain

Papers

Total porosity and open-pore porosity in the drying of fruits

Determination and correlation of heat transfer coefficients in a falling film evaporator

Retention of aroma compounds in basil dried with low pressure superheated steam

Mathematical modeling of moisture evaporation from foodstuffs exposed to subatmospheric pressure superheated steam

Optimum operating conditions in drying foodstuffs with superheated steam