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MAY 2017 FOOD FOCUSTHAILAND
(Antioxidant).For redpepper, thedryingprocesscanmaintain redness
and capsaicin content, while reducing the degradation of carotenoid
content, an important yellow pigment in pineapple. It also helps slow
the browning and other reactions that affect quality deterioration.
Freeze drying technique is becoming increasingly popular in food
processing industry toaddvalue to foodproductsas it providesahigh
qualityofproducts.Freezedryingcauses lessdamage to thesubstance
while the contraction of the cell structure is very small. In addition,
smells, flavors, and color of the food content generally remains
unchanged. Also, the appearance of the dried product remains the
same as it’s fresh. However, freeze-drying is a relatively more
expensiveprocess thanothermethods, itoften reserves for thehigher
economic value products. Currently, the machines for sublimation
freezedrying technologycanbemanufactureddomestically, resulting
in lower production costs and is more likely to bring into use at the
industrial level.
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Figure 2
Phase diagram of water and dryingmethods condition
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Creating a vacuum condition by removing air from the system
can lower the temperature of the water phase. During vacuum
formationof thesystemwhile theair isbeingevacuated, it givesan
advantage inmaintaining theproductqualities.Since thecontinuous
air removal reduces theoxidation reaction, it results in lossofproduct
quality during the drying process, where oxygen is the primary
reactant. Nowadays, combineddryingwithmechanical energyand
thermal energycancreateavacuumconditionat 10-20MPaor can
change thewater phaseof theproduct in the temperature rangeof
55-65 °C. Drying can be divided by heat transfermechanisms and
heatingenergy resources suchas vacuumdrying, electromagnetic
drying (Infraredormicrowavewaves),vacuumsystem, respectively.
However, theabove-mentionedhybriddryingsystem isachange
in the phase of the water from liquid evaporated to vapor. In this
step, if a vacuum pressure falls below 610.5 Pa, it will come to a
condition that thewaterphase insolidstatuscanbesublimeddirectly
to vapor phase. Therefore, for the freeze-drying techniques, food
products will be frozen at -10 to -18 °C, then the pressure in the
system will be reduced to absolute vacuum as described above.
This brings about a change in the vacuumpressure condition. The
food gets heated under such conditionwhile ice crystals in frozen
foodwill sublimateor change itsstatus fromsolid tovapor,whereby
the amount of ice crystals in the food becomes sublimated and
evacuated by a vacuum pump.
Today, drying byMultiprocessingDryers has been used at the
industrial level todevelopqualitystandards foragricultural products
and dried food products in both batch and continuous forms.
Especially for drying herbs, this technology can help increase the
valueof theproducts, suchas turmericand
Ganoderma
, which the
drying process helps to reduce the rate of oxidative deterioration
happens at the low temperature. Therefore, evaporation under
vacuum can occur at low temperatures (Depending on the vacuum
condition of the system). Figure 2 shows evaporating points
from various drying methods. This is to say, in hot air drying, the
evaporation of water contained in the product occurs at the
atmosphericpressure (Combinedmodesof heat transfer dryersand
Multistage dryers).
