D. Salvatori

Structural changes in apple tissue during glucose and sucrose osmotic dehydration: shrinkage, porosity, density and microscopic features

Abstract Micro- and macrostructural changes in apple slices during osmotic dehydration were studied. Samples were immersed into 25.0% (w/w) glucose or 34.6% (w/w) sucrose aqueous solutions at 30 °C until water and solid contents were almost constant (≅350 min). They were removed after selected times, and examined for thickness, volume, bulk and solid–liquid densities, porosity, water activity, water loss, solids gain and microscopic aspects. At relatively short times, significant weight and volume losses were observed for both treatments arising from the fast water loss. The solid–liquid density of glucose or sucrose treated samples increased slowly along the process. However, the bulk density increased up to a certain value and then fluctuated with increasing time, showing in some cases another pronounced increase for long times of treatment. Fruit porosity values decreased in line with the increase in bulk density values. At the end of the osmotic treatments in glucose or sucrose solutions, there was a recovery in porosity, although the values were lower than for fresh fruit. The changes in bulk density, porosity and volume of apple tissue along osmotic process were closely supported by microstructural and structural observations (using light microscopy and environmental electron scanning microscopy) and explained by considering osmosis as a multicomponent diffusion process through porous media and due to the relaxation of the viscoelastic shrunken cell walls.

Air drying behaviour of apples as affected by blanching and glucose impregnation

The effect of blanching and/or glucose impregnation at atmospheric pressure or in vaccum on the kinetics of moisture transfer during the first falling rate period of air drying of apple was analyzed. The moisture diffusivity of water (Deff) was strongly decreased by glucose uptake during impregnation step as well as volume shrinking. Studies of the cell structure using transmission electron microscopy revealed that both pretreatments did not modify in a great extension the cell wall resistance to water flux.

STRUCTURAL CHANGES AND MASS TRANSFER DURING GLUCOSE INFUSION OF APPLES AS AFFECTED BY BLANCHING AND PROCESS VARIABLES

ABSTRACT The effect of process variables and blanching on the rate of dewatering of apple slices through immersion in glucose solutions was analyzed. The adequacy of the Hawkes and Flinks and Pelegs models for fitting the rate data was evaluated as well as the structural changes produced in the tissue subjected to osmotic process. High concentration values (33-42 % (w/w)) of the soaking solution favored significantly water loss (WL) but only slightly affected solid gain (SG). Increasing system temperature over the range 20-50 °C generally provided an increase in WL and in SG. The increase in thickness decreased significantly both mass transfer rates. The use of sucrose instead of glucose lead to a greater SG while blanched samples showed higher rates of WL and SG. Microscopic studies revealed that, when applying short treatments, cells appeared slightly shrinked and cells walls folded. After long treatments, although an extensive

Osmotic dehydration progression in apple tissue II: generalized equations for concentration prediction

Abstract In Part I of the present communication, osmotic dehydration experiments at atmospheric pressure were carried out using apple ( Granny Smith var.) slices (20 and 30 mm thick) at 20°C, 30°C, 40°C and 50°C. The slices were subjected to treatment for varying periods of time (0.5, 1, 2, 3, 6, 12, 22 and 34 h) by using a sucrose solution (65% (w/w) as osmotic agent following which, slices, 1.5 mm thick, were obtained to determine water and sugar contents throughout the sample thickness. In an attempt to understand the osmotic phenomena, an approach based on the “advancing disturbance front” (ADF) concept was developed. In this second part, generalized equations developed from the concept of ADF have been proposed to describe the kinetics of sample concentration changes either in terms of concentration profiles or average concentrations.

Note. Vacuum impregnation of banana (Musa acuminata cv. giant cavendish) / Nota. Impregnación a vacío de banana (Musa acuminata cv. giant cavendish

Vacuum impregnation of banana was analysed by a hydrodynamic mechanism to determine effec tive porosity (∈e ). In the initial experiments, the influence of the ripening degree and cut was deter mined without taking into account sample deformations caused by the pressure gradients; in these cases ∈ e decreased as maturity progressed. Important structural changes were observed 2-4 days after the bananas were purchased from the local market, probably due to the climacteric charac teristic of the product. Other experiments were carried out to analyse the coupling of the hydro dynamic mechanism (HDM) with deformation-relaxation phenomena (DRP) by varying the time of treatment; ε e values determined by this procedure were approximately 10.1% and significant deformation values in the vacuum step (γ e = 3.6%) were observed. The height/diameter ratio also seemed to influence the behaviour of the product to the HDM-DRP action. The most impregnated samples were the ones with a height half that of the banana diameter.

Uptake Kinetics and Absorption of Calcium in Apple Matrices

The purpose of this paper was to study the kinetics of calcium uptake of blanched and not blanched apple tissue during impregnation treatments under vacuum or/and at atmospheric pressure. The relative absorption of calcium in rats, regarding calcium carbonate as reference substance, was also analyzed as a first approach. Apple impregnation is conducted (with and without previous blanching in saturated vapor) in isotonic glucose aqueous solutions containing calcium gluconate and lactate. A 50 mm Hg vacuum pressure is applied for a time t1 (0—180 min) or atmospheric pressure is used for a process time t2 (0—7.5 h). Calcium uptake by apple tissue is influenced by system pressure, blanching, and impregnation time, reaching 500—4600 μg Ca/g according to process variables. Preliminary data of true calcium absorption ranges between 74 and 86% regarding calcium carbonate.