True Density and Apparent Density During the Drying Process for Vegetables and Fruits: A Review

Abstract

This review presents the concepts involved in determining the density of foodstuffs, and summarizes the volumetric determination techniques used to calculate true density and apparent density in foodstuffs exposed to the drying process. The behavior of density with respect to moisture content (X) and drying temperature (T) is presented and explained with a basis in changes in structure, conformation, chemical composition, and second-order phase changes that occur in the processes of mass and heat transport, as reported to date in the literature. A review of the empirical and theoretical equations that represent density is presented, and their application in foodstuffs is discussed. This review also addresses cases with nonideal density behavior, including variations in ρ s and ρ w as a function of the inside temperature of the material, depending on drying conditions (X, T). A compilation of studies regarding the density of dehydrated foodstuffs is also presented.

True, Particle, and Bulk Density of Shrinkable Biomaterials: Evaluation from Drying Experiments

“…The significant similarity between particle and true density creates some confusion in interpretation. Despite the classical definition of true density as solid density, [2][3][4][5] some research publications [6][7][8][9] interpret true density as particle density. However, from the definition [Eq.…”

Determination of bulk density of Mirabelle plum during hot air drying as influenced by ultrasound-osmotic pretreatment

“…On the other hand, at constant ultrasonication time and osmotic solution concentration, increasing immersion time from 60 to 240 min generally increased bulk density; however, this increase was not statistically significant (p [ 0.05). This phenomenon has been attributed to the increase in solids during the osmotic process [5]. Koc et al [3] also showed that osmotic dehydration pretreatment increased bulk density of quince during drying.…”

“…During drying, moisture transport is strongly affected by changes in structural properties. Thickness, the formation of channels, and pore distribution all represent a preferential path for moisture transport [5]. Bulk density is also of importance to food quality and, therefore, has significant impact on the consumer's choice.…”

“…It is also equally important in the development of new industrial products with specific desired properties. Knowledge of the density variation of dried food materials is essential in the design of not only food processes but also the processing equipment [5,9].…”

Volume estimation of strawberries, mushrooms, and tomatoes with a machine vision system

“…The buoyant force method for apparent volume determination is especially useful with solid objects that do not absorb liquid easily. [11] Since the shape of many fruits and vegetables resemble some regular geometrical objects, the use of theoretical estimation with certain numerical techniques can be used to estimate their volume. Sabliov et al [12] developed an image processing method for ellipsoidal agricultural products including eggs, lemons, limes, and peaches assuming that each product has an axisymmetric geometry and is a sum of superimposed elementary frustums.…”