advances in drying and dehydration in fruit crops
TRANSCRIPT
RECENT ADVANCES IN DRYING AND DEHYDRATION TECHNOLOGY
Presented By
Manohar Lal Meghwal
Ph.D Horticulture (Pomology and floriculture)
Dept. of Pomology & Floriculture
College of Horticture
Kerala Agricultural University,Vellanikkara,Thrissur
Points to be covered during seminar Introduction
Importance of drying and dehydration of fruits
Nutritive value of dried fruits
What is drying and dehydration of fruits
Comparison between drying and dehydration
Principle of drying and dehydration of fruits
Pre treatment for the product to be dried
Post drying products treatments
Schedule for drying of fruits
Types of dryers
Conclusion
Sun drying is one of the oldest method of preservation of fruit, which is
simple, easy to carry out and ecofriendly.
Sun radiation is oldest and simplest method of drying.
Sun radiation are mostly available throughout the year during day time
in India.
Averagely 10-12 hrs sunlight is available in India.
The modern method of dehydration, i.e. drying fruit under controlled
atmosphere is however assuming importance now a days.
Among the different methods of processing dehydration techniques has
been found most useful in fruits especially in tropical fruits.
Modern production technology has greatly increased the yields of fruits.
But unfortunately, one-fourth of the highly perishable produce after
harvested is never consumed due to spoilage during its storage,
transportation and processing.
Preservation of fruits by drying and dehydration is highly effective and
practicable.
Dehydrated fruits have been an important food supply in different parts
of the world for military operations during the major wars because of its
space and weight saving possibilities.
IMPORTANCE OF DRYING AND DEHYDRATION OF FRUITS
Dried fruits have higher shelf life under proper storage conditions.
Transportation, handling and storage costs are reduced..
Microorganisms are effectively killed when the internal temperature is higher of fruits.
Dried fruits are tasty, nutritious, light in weight and easy-to-store.
Economical value of fruits is increased after drying and dehydration.
NECESSITY OF DRYING AND DEHYDRATION OF FRUITS
NUTRITIVE VALUE OF DRIED FRUITSDried fruits are good source of energy because they contain
concentrated fruit sugars.
Fruits also contain large amount of CHO, vitamins, proteins, fats
and minerals..
Approximate nutritive value of some dried fruits is as follows
(Source: Verma and Joshi, 2006)
Contents Fruits
Water(%)
Proteins(%)
Carbohydrates(%)
Fats(%)
Ash(%)
Apple 23 1.4 73.2 1.0 1.4
Fig 24 4.0 68.4 1.2 2.4
Raisin 24 2.3 71.2 0.5 2.0
Prunes 24 2.3 71.2 0.6 2.1
NUTRITIONAL COMPARISON BETWEEN FRESH AND DRIED APRICOT
(Per 100 gram)Contents Fresh Apricot Dried Apricot
Energy (kcal) 48 241 (500 %)
CHO (g) 11 63 (572 %)
Sugar (g) 9 53 (600 %)
Dietary fibre (g) 2 7 (350 %)
Fat (g) 0.4 0.5 (125 %)
Protein (g) 1.4 3.4 (250 %)
Vitamin A (ug) 96 180 (200 %)
Vitamin C (mg) 1094 2163 (200 %)
Iron (mg) 10 1
(Source: Verma and Joshi, 2006)
WHAT IS DRYING OF FRUITS ? It is removal of water from the fruit by conventional energy
sources like sunlight and wind under natural condition .
WHAT IS DEHYDRATION OF FRUITS ?
It is the process of removal of water from the fruit under controlled
conditions like temperature, relative humidity and air flow with the
help of mechanical instrument and modern techniques.
COMPARISON BETWEEN DRYING AND DEHYDRATION
Drying Dehydration
Drying is carried out in open natural
condition.
Dehydration is carried under
controlled condition.
Losses of fruit quality such as
colour, test, nutrient content is more
drying than dehydration process.
Losses of fruit quality are minimised
in dehydration.
Drying is cheapest method. Dehydration is costly method.
It takes more time. It takes less time.
Source of energy require freely
available.
Source of energy is costly.
Most fruits contain enough water to permit their spoilage by the
micro-organisms and enzymes.
By reducing the free water content, thereby increasing osmotic
pressures, microbial growth can be controlled.
The dehydration reduces the amount of available moisture i.e. the
water activity and hence, produce becomes shelf stable and is
preserved for quite a long period because of removal or binding of
water.
The basic principle in the process of drying or dehydration is the
removal of sufficient moisture to protect the product from spoilage.
PRINCIPLE OF DRYING AND DEHYDRATION OF FRUITS
PRE TREATMENT FOR THE PRODUCT TO BE DRIED Harvesting
To obtain high quality dried fruits the raw product must be harvested at
optimum maturity and processed carefully and as rapidly as possible.
Washing Fruits are usually rinsed in cold water at the drying plant to remove surface
dust particles and pesticides spray residues.
Peeling and Slicing Apples and sometimes cling-stone peaches are peeled prior to drying. This is
accomplished by various means: refractory, lye, hot brine peelers, mechanical
knife peelers for apples, and dilute lye for cling-stone peaches.
Pricking Pricking aimed at making the structure more porous so as to facilitate mass
transfer and thereby, speedup drying rate
Generally pricking is followed in Aonla fruit.
SoakingThe fruits slices are soaked in plain water, lime water, brine or alum solution
for few hrs to few days before blanching and cooking
Curing Generally is curing is practiced in vegetables (onion , garlic).
It dehydrates raw material by sun drying or by hot air drying at a
temperature of 30°C.
Blanching
Exposing fruit to hot or boiling water-as a pre-treatment before
drying has the following advantages:
It helps to clean the material and reduce the amount of
microorganisms present on the surface.
It preserves the natural colour in the dried products.
It shortens the soaking and/or cooking time during
reconstitution.
POST DRYING PRODUCT TREATMENTS The procedures after drying vary with the kind of dried fruits, however, the practices which are followed after drying are described as follows
Screening
During cutting operation leave some unwanted size of the product
which have to be screened.
Inspection The dried product is inspected to remove the discoloured pieces such as
skin or stem particles. These are removed manually.
Heat treatment To avoid insect infestation, great care is necessary while storage . In case of
heat treatment, dried at 54-65oc to destroy all insects.
Sweating Sweating is a practice of storage of dried product in bins or boxes
for equalization of moisture or re-addition of moisture to a desired
level. It is used primarily with some dried fruits and some nuts.
Packaging Most products are packaged after drying for protection against
moisture, contamination with micro-organisms and infestation with
insects, although some dried fruits may be held as long as a year
before packaging.
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Fruit Preparation and pretreatment
Sulphuring time
Drying temperature
Mango Wash, peel, cut into 12 mm thick slices
2 hrs 45-500C or sun dry
Banana Wash, peel, halve lengthwise or slice crosswise 12 mm thick
30 min 55-600C or sun dry
Papaya Wash, peel, remove seeds and cut into 6 mm thick slices
2 hrs 60-650C or sun dry
Fig Wash 1 hrs 55-600C or sun dry
(Source: Sanjeev Kumar et al., 2003)
Fruits
Blanching
Peeling
Drying
Sulphuring usually @1.8 to 3.6 kg per ton of fruit
Packing (Airtight in tin containers or polythene bags)
Washing
(Srivastava and Sanjeevkumar ., 2006 )
Types Types of of
dryers dryers
SUN DRYING Prepared fruits are placed on drying trays. Stainless steel screening
and thin wood lath are good materials for home-constructed drying
trays (14" x 24" x 1“)
Sun drying of fruits is practiced in tropical and subtropical regions,
where there is plenty of sunshine and practically little or no rains during
the drying season. It is carried out in the open sun. Equipment
essentially consists of drying trays and few other items.
SOLAR DRYINGRecent efforts to improve on sun
drying have led to solar Drying.Solar drying uses the sun as
the heat source.A foil surface inside the dehydrator
helps to increase the temperature, from 37-930C.
Ventilation speeds up the drying time.
Shorter drying times reduce therisks of food spoilage or mould growth.
SPRAY DRYINGSpray drying is the current state of the art in the food industry, because
it offers an excellent solution to many drying problems.
There are three basic types of devices:
1. single-fluid nozzles (pressure type)
2. Two-fluid nozzles (pneumatic type)
3. centrifugal feeds (spinning disks)
Due to correct balance of dryer inlet and
outlet temperatures can reduce energy use.
These 3-stage dryer is used for "non-dusty,
hygroscopic, and high fat content products.
It suitable for drying juices and Powder.
FREEZE-DRYINGFreeze-drying is the drying of material in the frozen state at 0oc. It is usually carried out under vacuum, at absolute pressures that readily permit ice to change directly from solid to vapour. Advantages
Good retention of volatile flavors .Good vitamin retention. Rapid rehydration ratio. Long product storage life.
DisadvantagesHigh drying cost.Damage to certain products by initial freezing. Product friability (crumbles easily). Pre-treatment sometimes necessary (e.g., with carrots) to avoid colour loss.
Sr. No.
Conventional drying Freeze drying
1 Conventional drying is a continuous processing
Freeze drying is a batch processing
2 Temperature between 37 and 930C generally used
Sufficiently low temperature is used to prevent thawing
3 Drying usually at atmospheric pressure
Drying usually below 4 mm Hg pressure
4 Drying time may be short, usually less than 12 hours
Drying time generally between 12 and 24 hours
5 Colour usually darker Colour usually natural
6 Flavour may be abnormal Flavour generally natural
7 Storage stability good, tendency to darken
Storage stability excellent
8 Costs generally low Costs generally high
DIFFERENCE BETWEEN CONVENTIONAL AND FREEZE DRYING
(Source: Sanjeev Kumar et al., 2003)
FREEZE DRIED STRAWBERRY SLICES
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OVEN DRYING It is the combining factors of heat, low humidity and air flow, an oven
can be used as a dehydrator.
Oven drying is slower than dehydrators because it does not have a
built-in fan for the air movement.
It takes about two times longer to dry fruits in an oven than it does in
a dehydrator. Thus, the oven is not as efficient as a dehydrator and
uses more energy.
An oven is ideal for drying of banana chips.
A specially made structures are used for drying.
The infrared radiations from sun is absorbed.
About 300 to 400 nm wave length rays are trapped and used for drying.
These infrared rays are having a shorter wave length and having a higher
penetrate capacity thus helps in rapid removal of moisture.
INFRARED DRYING G
VACUUM DRIERS Internal pressure as much as
9800 kg/m2 by supply of heat.
Heat transfer to fruit is largely
by conduction and radiation.
Water removal are conducted by
regulating the degree of vacuum
and intensity of heat input.
Higher quality of dried fruits.
OSMOTIC DEHYDRATION
Material is soaked in a heavy (thick liquid sugar solution) and/or a
strong salt solution.
Protective effect on colour, flavor and texture.
Initial temperature 430 c and increased up to 66-710c.
The protective effect remains throughout the drying process and
makes it possible to produce dried products of high quality.
This process makes little use of sulphur dioxide.
Changes in moisture, total soluble solids, pH and acidity during Osmo-Air drying of
Papaya Parameters Initial After blanching Final ( After
drying)Moisture (%) 86.12 82.11 12.06
TSS (%B) 08 13 77
pH 5.51 5.46 5.48
Acidity (as % anhydrous citric acid)
0.12 0.14 0.135
(Source: Jasim Ahmed et al.,1995)
CABINET DRIERUsually fruit slices are loaded on tray in a thin layer.
Fresh air is blown into a cabinetor, then it is drawn by the fan
through a heater coil and then it is blown across the fruits
slices/pieces.
Suitable for small scale operation.
Operated at air temperature of
about 950c with air velocity
2.5-5 m/sec across tray.
Drying time may be 10-20 hrs.
MICROWAVE VACCUM PROCESS (MIVAP)
An innovative Technology for the Production of high-qualityDehydrated Food Products
The physical mechanism involved in heating and drying with microwaves is distinctly
different from those of conventional means.
Microwaves can penetrate into dielectric materials and generate internal heat.
The internal heat generated establishes a vapour pressure within the product and
gently pumps the moisture to the surface.
Because of this moisture pumping effect, the moisture is pumped to the surface and
case hardening does not occur, enabling increased drying rates and improved
product quality.
Drying and dehydration increases fruit value.
The modern method of dehydration, i.e. drying fruit under controlled
atmosphere is however assuming importance now days.
• Water removed from food is primarily done to lower the water activity so
that microbial growth is inhibited.
• Drying and dehydration minimizing losses of fruit crops when they are
available in large quantity
• It also saves energy, money and space in shipping, packaging, storing
and transportation.
• In recent years, the achievement in drying or dehydration of fruits have
led to the development of more improve methods and techniques.
CONCLUSION