57
Superheated Steam Drying
A steam having a temperature higher than the saturation temperature at a given pressure is defined as superheated steam. The superheated steam at atmospheric pressure is referred to as an alternative drying medium for materials that can withstand
temperatures above 100 °C. The overheated steam drying method is distinguished
from the conventional methods by having long constant rate periods and lower critical moisture content. High drying efficiency, no oxidation risk, no pollutants,
smaller equipment use, better antimicrobial effect are the advantages of overheated
steam drying (Devahastin and Mujumdar 2014).
This method is reported to be a suitable method for drying shrimps. This is
because boiling and drying takes place in a single step, due to the use of overheated
steam as the drying medium. Since it eliminates the boiling stage, it also prevents
any nutritional losses during boiling (Prachayawarakorn et al. 2002).
Namsanguan et al. (2005) studied drying of shrimp using a superheated steam
dryer and investigated a two-stage drying. In the first stage, the shrimps were dried
by a superheated stem dryer and in the second stage by the hot air dryer. According
to the results obtained, in the two-stage drying dryer compared with the single-stage
superheated steam dryer, in the shrimps lower shrinkage degree, higher degree of
rehydration, better colour, less hard and soft and more porous structure were
observed.
Drying in Spouted Jet Bed
It was determined that required drying time and energy reduced for drying of the
shrimp in a spouted jet bed dryer compared to conventional tray dryers. In addition,
the drying temperature and shrimp size also affected the quality characteristics of
the dried shrimp. For small and large shrimps, sensory sensitivity at temperatures of
100 and 120 °C was found to be at the highest level (Niamnuy et al. 2007).
Tapaneyasin et al. (2005) investigated the effects of inlet drying air temperature
on the drying kinetics and various quality attributes of shrimp dried in a jet‐spouted
bed dryer. The results showed that low shrinkage, high rehydration, low maximum
shear force, and high value of redness were observed when a constant inlet air temperature of 100 °C was used.
Changes in Shrimp Muscle During Drying
Protein denaturation that occurs during the drying process significantly affects the
quality characteristics of the dried products. As a result of protein denaturation,
protein chains are opened, and free carboxylic and amino groups appear. The
exposed sulfhydryl groups are oxidized to form disulphide bonds. The solubility of
the proteins decreases due to these changes in the protein structure. Drying methods
and drying parameters have important effects on protein denaturation (Nguyen
et al. 2014).
2.1 Shrimps/Prawns
Superheated Steam Drying
A steam having a temperature higher than the saturation temperature at a given pressure is defined as superheated steam. The superheated steam at atmospheric pressure is referred to as an alternative drying medium for materials that can withstand
temperatures above 100 °C. The overheated steam drying method is distinguished
from the conventional methods by having long constant rate periods and lower critical moisture content. High drying efficiency, no oxidation risk, no pollutants,
smaller equipment use, better antimicrobial effect are the advantages of overheated
steam drying (Devahastin and Mujumdar 2014).
This method is reported to be a suitable method for drying shrimps. This is
because boiling and drying takes place in a single step, due to the use of overheated
steam as the drying medium. Since it eliminates the boiling stage, it also prevents
any nutritional losses during boiling (Prachayawarakorn et al. 2002).
Namsanguan et al. (2005) studied drying of shrimp using a superheated steam
dryer and investigated a two-stage drying. In the first stage, the shrimps were dried
by a superheated stem dryer and in the second stage by the hot air dryer. According
to the results obtained, in the two-stage drying dryer compared with the single-stage
superheated steam dryer, in the shrimps lower shrinkage degree, higher degree of
rehydration, better colour, less hard and soft and more porous structure were
observed.
Drying in Spouted Jet Bed
It was determined that required drying time and energy reduced for drying of the
shrimp in a spouted jet bed dryer compared to conventional tray dryers. In addition,
the drying temperature and shrimp size also affected the quality characteristics of
the dried shrimp. For small and large shrimps, sensory sensitivity at temperatures of
100 and 120 °C was found to be at the highest level (Niamnuy et al. 2007).
Tapaneyasin et al. (2005) investigated the effects of inlet drying air temperature
on the drying kinetics and various quality attributes of shrimp dried in a jet‐spouted
bed dryer. The results showed that low shrinkage, high rehydration, low maximum
shear force, and high value of redness were observed when a constant inlet air temperature of 100 °C was used.
Changes in Shrimp Muscle During Drying
Protein denaturation that occurs during the drying process significantly affects the
quality characteristics of the dried products. As a result of protein denaturation,
protein chains are opened, and free carboxylic and amino groups appear. The
exposed sulfhydryl groups are oxidized to form disulphide bonds. The solubility of
the proteins decreases due to these changes in the protein structure. Drying methods
and drying parameters have important effects on protein denaturation (Nguyen
et al. 2014).
2.1 Shrimps/Prawns