الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 217 |  |  |
| | | from | 217 | | |
Abstract
Freezing process is very powerful in preserve of fruits and vegetables cteristics, but it causes the chemical and physical changes which lead loss of quality. The outcome of this process is mainly due to the hanical damage caused from ice crystals. Osmotic dehydration (aD) is a
ful technique to modify fruits and vegetables composition and prepare to freezing process. Osmo-dehydrofreezing (ODF) refers to the bined process of partial drying in a concentrated solution (osmotic ydration) followed by freezing. The present investigation starts with aim of studying and improving frozen fruits and vegetables quality to oid the cellular structure loss, that caused by chemical and physical asures of freezing by applying the osmotic dehydrofreezing process. This hnique permits to introduce cryo-protective agent into the food matrices.
arious osmotic agents such as sucrose, glucose, fructose, sodium chloride, d (sucrose/ sodium chloride) combinations, have been used for osmotic hydration due to the applied experimental design. The mass transfer havior during osmotic pre-treatment was studied. The research was cusing in the developments of value-added fruits (dates, apples and ricots) and vegetables (carrots, tomatoes and strawberries) products using motic as a pretreatment steps. The final products were ODF products of
-hole, halves and disks. The influence of sugar solution concentration (50% 70 %), process temperature (30°C to 50 0q, sample to solution ratio (1/4 1/12) and process time (2 to 24 hrs) on the water removal and solid gain characteristics of apricots, apples, strawberries and dates samples were investigated. Carrot disks were subjected to binary osmotic solutions of salt solution and sucrose solution (1: 1) as follow: 5% salt solution + (30, 40 and 50%) sucrose solution or 10% salt solution + (30, 40 and 50%) sucrose solution and 15% salt solution + (30, 40 and 50%) sucrose solution. Whereas, whole tomatoes were soaked in salt at 5,10,15,20 and 25%; sucrose at 5,10,15,20 and 25% and multi-components of salt: sucrose (3 :2) at 10, 15, 20 and 25% or sucrose: salt (3: 1) at 10,20,25,35 and 45 % as osmotic solutions. Besides, this work was also aimed to analyze the effects of ODF on the physicochemical and quality parameters (color, pH, total
1. Mass transfer rates during osmotic dehydration are influenced by several factors which can be used for process optimization. In general, the rates of water loss, WL were much higher than those of solid gain, SG during the osmotic processing. Obviously with an increase in osmotic treatment time, mass transfer process increased till both water and solute concentrations attain their equilibrium conditions. However a longer contact time of the samples with the sugar solution gives a higher SG. Higher process temperatures seem to promote faster mass transfer (water loss and solids diffusion within the product). Sucrose and NaCI concentrations in the osmotic solution critically influence mass transfer parameters. However, NaCI concentration was greater influence than sucrose concentration. In addition, increased osmotic solution to sample mass ratio resulted in an increase in both WL and SG. Furthennore, higher specific surface area samples (such as halves and disks) favored elevated WL and SG.
2. All salt-sucrose binary mixtures showed valuable synergistic effect to develop high osmotic potential; because of pressure variation with respect to the molecular weight of the osmotic agent.
without sugar. As a res (70%), a technical pro viscosity (neglecting hi between 60% and 70% high SG is undesirabl concentration.
acidity, anthocyanins, total carotenoids, lycopene, salt and vitamin C). Microstructural changes during ODF were also determined.
The obtained results are consistent with the following specific conclusions:
5. The experimental data solution, as reuseforat
6. The frozen sample osmo-dehydrofrozen of the products prot
7. WL and SG during observed to have s several fruits and
3. These studies established that the mass transfer in natural tissues is not simply a diffusion phenomenon and that cell membrane represents the major resistance to the mass transfer in such systems. Concerning the investigated fruit materials, a descending order of WL can be seen during this study due to differential permeability of cellular membrane as well as the special geometry of the fruits exposed to the treatment as follow:
Apple disks> strawberry halves> apricot halves> date halves. It is mainly.
8. The study demo important intrins’ vi tam in C, anth solution, Sugar jam as it exhibits for production 0
9. In terms of discoloration. the presence browningb,r
4. The presence of sugars provided protection during freezing, allowing firmer tissue than for fruit treated in the same manner
10. The resu13 products I helps to’