PRESEVATION TECHNIQUE OF FRUITS AND VEGETABLES

1. OSMATIC DEHYDRATION OF FRUITS AND
VEGETABLES PROCESSING
Presented by
N. SAI PRASANNA
Roll No.: 17AG63R20
Department of Agriculture and Food Engineering
IIT Kharagpur

2. CONTENTS
•Introduction
•Principles of osmatic dehydration
•Factors affecting OD
•Different osmatic agents and their effects
•Flow chart of OD process
•Advantages
•Drawbacks
• Case study

3. INTRODUCTION
•Osmotic dehydration is process of immersing cellular
materials into a concentrated solution for partial
removal of water while increasing the solid contents.
•The complex cellular structure, the cell wall and the
surface of the tissue acts as a semi-permeable surface.
•It is a low temperature process.

4. PRINCIPLE OF OD
• The underlying principle is that water diffuses from dilute
solution (Hypotonic solution) to concentrated solution
(Hypertonic solution) through a semi-permeable membrane
till equilibrium is established.
• The driving force for water removal is the concentration
gradient between the solution and the intracellular fluid.
• If the membrane is perfectly semi-permeable, solute is unable
to diffuse through the membrane into the cells.

5. FACTORS AFFECTING OD PROCESS
• Types of osmotic agent
- molecular weight and size
- ionic state and pH
- solubility of the solute
- chemical composition and structure
• Concentrations of osmotic agent
• Processing temperatures
• Agitation or stirring process
• Osmatic solution to food mass ratio
• Geometry of the food material

6. DIFFERENT OSMOTIC AGENTS & THEIR EFFECTS
OSMOTIC
AGENT
EFFECT
Calcium
Chloride
Increases the firmness of fruits and preserves the
texture during storage.
Ethanol Decreases viscosity and freezing point of the
osmotic solution in cooling and freezing processes.
Fructose high water loss and low solid gain. Increases the
dry matter content and water activity of the final
product is also lower.
Lactose It has much lower level of sweetness than sucrose.
Low solubility in aqueous solution

7. OSMOTIC AGENT EFFECT
Malto Dextrin It can be used as an osmosis solute at higher
total solids concentratioor in mixed systems
High solid gain
Sodium Chloride Mostly used for vegetables as it retards
oxidative and non-enzymatic browning.
Sucrose / Sugar high water loss and low solid gain; it
reduces browning by preventing the entry of
oxygen.
Starch / Corn syrup Favours similar final water content with
minimal solid gain.
SOURCE: International journal of preservation of fruits and vegetables.

8. Flow chart of osmotic dehydration process
Selection of raw material
Washing
Preparation of fruits
Osmatic
treatment
DrainingPretreatment
Packaging
Dehydration of
fruits slices
Storage
Peeling
Labeling

9. ADVANTAGES
•Quality improvement in terms of color, flavour or aroma
and texture.
•Energy efficient as compared to other dehydration
techniques namely air, vacuum and tray drying.
•More product stability during storage due to low water
activity by solute gain and water loss.
•Flavor retention is also more when sugar or sugar syrup is
used as an osmotic agent.
•There is minimum loss of color, flavor and nutrients.

10. • It increases resistance to heat treatment.
• Acid removal and sugar uptake by fruits modifies the
composition and improves the taste and acceptability.
• It prevents the enzymatic browning and inhibits activities of
polyphenol oxidases.
• Constant immersion of product in osmotic agents avoids the
oxygen exposure, the product retains better colour.
• It helps to retain the shape of the dehydrated products.
• The process could prove to be good for production of the ready
to eat foods such as raisins etc.

11. • The process reduces volume of the products thereby saving in the cost of
processing, storage and transport.
• It protects against structural collapse of product during drying.
DRAWBACKS:
• The reduction in acidity level reduces the characteristic taste of some
products. This can be overcome by adding fruit acid in the solution.
• Solute uptake and leaching of valuable product constituents often lead to
substantial modification of the original product composition with a
negative impact on sensory characteristics and nutritional profile.
• Sugar uptake results in development of a concentrated solids layer under
the surface of the fruit, upsetting osmotic pressure gradient across the
fruit interface and decreasing the driving force for water flow.

12. CASE STUDY
TITLE:
Effect of osmotic dehydration process on the physical,
chemical and sensory properties of osmo-dried
cantaloupe
AUTHORS:
1.Phisut, N.,
2.Rattanawedee, M. and
3.Aekkasak, K.
JOURNAL :
International Journal of Food Science and Technology
Year of published: 2013.

13. Objectives
•To investigate the effect of osmotic dehydration process
on the physical, chemical and sensory properties of osmo-
dried cantaloupe.
•The pre-treatment effect of calcium salts (calcium
chloride and calcium lactate) on the firmness(structure) of
fresh cantaloupe was investigated.
•Two osmotic dehydration methods including fast osmotic
dehydration (FOD) and slow osmotic dehydration (SOD)
commonly use to produce osmo-dried fruit.

14. MATERIALS AND METHODS
Collection of Material
Cantaloupe with 10–11% TSS
Sample preparation
The fruits were washed, hand-peeled and cut into
slices with approximately 3×3.5×1.5 cm.
Pretreatment process
The slices were immersed in two calcium sources
(calcium chloride and calcium lactate) at two
concentrations (2% and 3%) for 5 h.

15. OSMOTIC DEHYDRATION PROCESS
Two osmotic dehydration methods (FOD and SOD)
performed under temperature 30°C at 1:3 (fruits : osmotic
solution).
FOD - immersed continuously in 50°Brix sucrose solution
for 24 h and then washed in water (50°C).
SOD - 30°Brix sucrose solution for 24 h, 40°Brix sucrose
solution for 24 h, 50°Brix sucrose solution for another 24 h
and then washed in water (50°C).
Dried by using hot air oven at 60°C until the moisture
content was below 18%.

16. PHYSICAL PROPERTIES MEASUREMENT
Colour and texture measurement
Hunter Lab colorimeter
Texture analyzer
Browning measurement
1. 20g sample was rehydrated for 10 min in 50 ml acetic
acid and homogenized for 5 min.
2. Then diluted to 200 ml with acetic acid solution.
3. The mixture was filtrated through filter paper.
4. The clarified sample solution was measured browning
intensity by spectrophotometer at 420 nm.

17. CHEMICAL PROPERTIES ANALYSIS
Determination of pH
pH meter calibrated (buffers of 4.0 and 7.0)
at ambient temperature.
Determination of total acidity (% citric acid)
1. 10g sample homogenized in 30 ml of DW.
2. Made up to 50 ml and homogenate was filtered.
3. Centrifuged at 5000 rpm for 10 min.
4. The supernatant was titrated with 0.01N NaOH with
1% phenolphthalein solution as an indicator.

18. Determination of moisture content
1. 2-5 g of the sample was placed in a pre-dried aluminum
dish and dried in an hot air oven at 110°C for 6h.
2. Dried sample was placed in desiccator & cooled for 0.5 h.
3. The weight was recorded and moisture percent based on
the initial wet weight was calculated.
Determination of water activity (water activity meter)
1. The sample was cut into tiny pieces & inserted into sample cup.
2. This was made immediately to restrict moisture transfer from the air
to the samples.
Determination of total sugar & reducing sugar
(grams of glucose per 100 g of sample)
Volumetric method using titration with Fehling’s reagents.

19. Determination of vitamin C (mg of vitamin C/gm of sample)
1. 450 mg of sample extracted with meta phosphoric acid for 45 min
at room temperature.
2. Filtered through the filter paper.
3. The filtrate (1 ml) was mixed with 2,6-dichloroindophenol.
4. Absorbance measured within 30 min at 515 nm against a blank.
5. A calibration curve of L-ascorbic acid to quantify vitamin C content
Sensory analysis
1. Calcium-treated samples - texture and taste
2. The quality and consumer acceptability
- colour, appearance, flavour, texture and overall acceptability.
3. Colour - visual observation
4. Texture - eating
5. Flavour - smell and taste

20. RESULTS AND DISCUSSIONS
Physical properties of osmo-dried cantaloupe
L* = Lightness,
a* = Redness and greenness
b* = yellowness and blueness.
PROPERTIES FOD SOD
Colour L*
a*
b*
56.79 ±0.37
14.63 ±0.59
22.08 ±1.11
57.74 ±0.37
14.03 ±0.40
21.08 ±0.39
Hardness 21.35 ±0.41 18.05 ±0.63
Browning index 0.29 ±0.05 0.27 ±0.07

21. Chemical properties of osmo-dried cantaloupe
PROPERTIES FOD SOD
Moisture content (%) 14.78 ±0.23 14.08 ±0.53
Water activity (aw) 0.72 ±0.00 0.69 ±0.01
pH 5.44 ±0.13 5.72 ±0.13
Total acidity (% ) 0.12 ±0.03 0.07 ±0.00
Reducing sugar(%) 14.03 ±0.52 14.11 ±0.53
Total sugar (%) 39.25±0.56 44.57 ±0.68
Vitamin C (mg/100g) 30.01±0.58 19.21 ±0.61

22. Sensory evaluation of osmo-dried cantaloupe
cantaloupe slices immersed in various calcium salts
Sensory treatments FOD SOD
Colour 6.57 6.91
Appearance 6.17 7.15
Texture 6.11 7.05
Flavour 6.52 6.59
Calcium salts/Sensory attributes Texture Taste
Calcium chloride ( 2% for 3hr) 6.72 3.72
Calcium chloride ( 3% for 3hr) 6.78 2.77
Calcium lactate ( 2% for 3hr) 6.62 6.84
Calcium lactate ( 3% for 3hr) 6.74 6.56

23. CONCLUSION
• CaCl had higher firmness,
higher amount of free calcium ions available for pectin linkage and
all calcium ions are dissociated than calcium lactate.
• Low score of taste 2% or 3% of CaCl compared to calcium lactate.
• High concentration of CaCl may result in the bitter taste.
• Hence 2% calcium lactate for 3 hr proposed as an alternative
source of calcium to use for improvement the texture of cantaloupe.