Effects of Spray-drying Parameters on Water Activity, Color, and Oxidation
Of Whole Egg Powder
Nantika Thungmanee, Kanok-Orn Intarapichet, and Sukrit Thaiudom
School of Food Technology, Institute of Agricultural Technology, Suranaree University of Technology
Nakhon Ratchasima 30000, Thailand
Response surface design was used to determine the optimal condition parameters
of spray-drying. Nine different input variables, inlet temperatures and feed rates, were
performed in spray-drying of whole egg liquid. Water activity, browning color (as L
value) and TBARS of the powdered egg were determined. The central composite design
experiment was used for plotting the response surface curves. Increasing of temperatures
of inlet air from 114 to 156°C at feed a constant rate of 14 ml/min led to a decrease in
water activity from 0.399 to 0.186. On the contrary, TBARS values of the powdered egg
increased from 0.597 to 1.083 mg MDA/ kg when the temperatures increased, as well
color score (L value) increased from 88.92 to 92.14. Increasing feed rate from 6 to 24
ml/min at 135°C caused increasing in water activity from 0.212 to 0.372, but decreases in
color score from 91.40 to 89.19 and TBARS values from 1.069 to 0.564 mg MDA/ kg
were observed. Effects of spray-drying parameters were illustrated by the plots of surface
response curves. The optimal conditions for spray-drying of whole egg fluid regarding to
water activity, browning color, and TBARS values were at the inlet temperature of 135°C
and feed rate of 27 ml/min.
Keyword: Spray-drying, Egg powder, Water activity, Browning, Oxidation
Spray drying is the most widely used industrial process for drying. Small drops of
liquid sample are produced by atomization. The high surface of small drops involve in
high mass transfer rates, which lead to short dry time. The application of this drying
process to produce milk powder, soup, coffee, tea, etc. is already known (Fernández-
Pérez, Martín, Castro, 2004). Another use of spray drying is in the chemical and
biological industries, in which a wide variety of powder, granulated and agglomerated
products were manufactured (Janning, 1995; Muhammed, 1996).
Dried egg is widely used in food preparations because of their long shelf-life; in
fact, this product is usually stored without particular care (Caboni, Boselli, Messia,
Velazco, Fratianni, Panfili, & Marconi, 2005). However, the safety and quality of
powdered egg depend on the drying process. High surface area of small drops, high
temperature, and forced oxygen flow of drying system are factors promoting the chemical
modifications in powdered egg. Lipid oxidation and non-enzymatic browning reactions
are two main chemical modifications, which lead to undesirable compounds.
Lipid oxidation leads to lower the quality of powdered egg such as off-flavor and
toxic compounds. The determination of oxidation is measured by thiobarbituric acid-
reactive substances (TBARS).
Non-enzymatic browning reactions can arise during the processing of powdered
egg. The presence of proteins and reducing sugars in whole egg is the essential condition
for the non-enzymatic condensation of carbonyl and amino groups of sugars and protein
(amino acids) (Friedman, 1996). This reaction is responsible for the brown color
development and natural flavor compounds, which result in off-flavor and off-color of
powdered egg. Moreover, this reaction can produce mutagenic and carcinogenic
compounds which lead to the risk of cancer.
The production of droplets of given size and surface area by atomization is a
critical step in the spray drying process. The degree of atomization under a set of drying
condition controls the drying rate, and therefore the particle size (Fernández-Pérez et al,
2004). The parameters influencing sizing performance and powder qualities (low of lipid
oxidation and browning reaction) are concentration of the liquid whole egg, inlet air
temperature, and liquid feed flow rate.
The objective of this study was to evaluate water activity, color due to browning
reactions, and lipid oxidation of powdered egg as affected by two parameters of spray-
drying process; inlet air temperatures and feed flow rates. In addition, the response
surface design was used to determine the optimal condition parameters for spray-drying.
The central composite design experiment was used for plotting the response surface
Materials and methods
1. Preparation of the liquid whole egg
Chicken eggs were obtained from Suranaree University Farm, Nakhon Ratchasima
Province, Thailand. Liquid whole egg was prepared, mixed, filtered then, the solid
content was adjusted to 10% using a moisture balance (HA 300, Precisa, Switzerland).
The liquid whole egg was heated up to 40ºC before feeding to the spray-dryer (Niro
Mobile Minor ‘2000’ type E spray-dryer, GEA Niro A/S, Denmark).
2. Laboratory analysis
Water activity of dried egg powder was measure using AquaLab Model Series 3
TE (AquaLab, USA.).
TBARS analysis. Three gram of sample was mixed with 50 ml of deionized water,
adjusted to pH 1.5 with 4 N HCl. To the solution, 500 µl of 1.5% BHA in ethanol was
added. TBARS was determined by distillation method using 1,1,3,3-tetraethoxypropane
for construction of calibration curve. The absorbance was measured at 530 nm. TBARS
value was expressed as mg of malondialdehyde per kg of sample (mg MDA/kg).
Color measurement. Browning color (L value) was measured by using a Minolta
Chroma Meter (Minolta CR 300; Tokyo, Japan). The L value represents lightness,
negative towards black, positive towards white (Fredriksson, Elwinger, & Pickova, 2006).
Five random readings were made from the surface of sample.
3. Experimental design
The parameters or input variables selected for powdered egg characterization were
related to undesirable compounds that occur during the processing steps. The different
levels of inlet temperature and feed flow rates were related to the main chemical
modification, i.e. oxidation and browning reaction.
Response surface design was used to determine the optimal condition parameters
of spray-dried whole egg powder. The central composite design experiment was used for
plotting the response surface curves. Nine different input variables related to two main
factors, inlet air temperature and feed rate were used for spray-drying. The variables were
114 ºC and 14 ml/min, 120 ºC and 9 ml/min, 120 ºC and 21 ml/min, 135 ºC and 6 ml/min,
135 ºC and 14 ml/min, 135 ºC and 24 ml/min, 150 ºC and 9 ml/min, 150 ºC and 21
ml/min, and 156 ºC and 14 ml/min.
Results & Discussion
1. Effect of parameters on water activity
The effects of inlet air temperatures and feed rates on water activity (aw), TBARS
values, and L values of egg powder are shown in Table 1. Increasing of temperatures of
inlet air from 114 to 156° C at a feed rate of 14 ml/min led to the decrease in water
activity from 0.399 to 0.186. This result was similar to the work of Fernández-Pérez et al.
(2004) who found that at a constant feed rate, the higher temperature of inlet air was lead
to the faster of the moisture evaporation. In addition, at the temperature of 135°C, when
the feed rate was increased from 6 to 24 ml/min, the aw was found to increase from 0.212
to 0.372. At the low feed rate and constant inlet air temperature smaller droplets and
higher surface areas of egg powder were produced resulting in higher moisture
evaporation rate. Therefore, lower feed rate would lead to the lower of water activity.
Table 1 Mean value of water activity, TBARS and L values of whole egg powder
Feed rate (ml/min)
(mg MDA/ kg)
n = 6.
2. Effect of parameters on oxidation
Increasing of temperatures of inlet air from 114 to 156° C at the feed rate of 14
ml/min resulted in increasing of TBARS values from 0.597 to 1.083 mg MDA/ kg as
shown in table 1. In contrast, increasing feed rate from 6 to 24 ml/min at the temperature
of 135° caused a decrease in TBARS values from 1.069 to 0.564 mg MDA/kg.
The results in Table 1 show lower oxidation occurred when aw were in the ranges
of 0.237 to 0.399 and increased as water activity of the powder egg decreased. The
relationships between lipid oxidation rates and water activity of dried product were
observed. The oxidation decreased as the aw increased up to 0.2-0.4. Angelo (1992)
reported that water in food decreased the free radical concentration by promoting
termination of oxidation reactions. Thus, this led to a recombination of free radicals to
form nonradical products resulting in reducing the oxidation rate. At low aw, sufficient
water was not available to reduce the free radical concentration (Angelo, 1992).
Therefore, the oxidation rate at low water activity was high.
3. Effect of parameters on Browning
Browning of whole egg powder was characterized by color measurement of L
value. The L value represents lightness, negative toward black, positive toward white.
Hence, the lower L value indicated that a strong browning reaction had occurred. Table 1
shows the effect of spray-drying parameters on browning of egg powder. The inlet air
temperature at 114°C and feed rate of 14 ml/min gave low L values, indicating strong
browning. The high L value (lighter color) was observed when the inlet temperature was
at 150°C and flow rate of 9 ml/min. The browning intensity was related with water
activity in egg powder. When the inlet temperature was set at 114°C and feed rate of 14
ml/min, the product had the aw of 0.399, while at 150°C and 9 ml/min, the water activity
of 0.150 was observed. The browning of the egg powder reached maximum at aw of 0.4-
0.8. This indicated that water may accelerate browning by imparting mobility to the
substrates (Leung, 1992). Therefore, the strong browning reaction occurred when water
activity of the product increased up to 0.399.
4. The optimal conditions of spray-drying process
The optimal conditions were determined by using response surface design. Nine
different input variables consisted of two main parameters; inlet air temperature, and feed
rate. The aw, browning color (measured as L value) and TBARS values of whole egg
powder were used as the output responses. Figure 1 shows the effects of both input
parameters on the qualities of whole powder egg products. It was observed that
temperature and feed rate of spray-drying process had an effect on oxidation and
browning of the powdered egg. Water activity is normally used for controlling lipid
oxidation of dry food products. There are several papers reporting oxidation decreases as
the aw increases up to 0.2 to 0.4 (Nelson & Labuza, 1991). In this study, the optimum
spray-drying process gave the powdered egg that had aw ranged 0.2 to 0.4. Figure 1a
shows that to obtain aw of the product between this range, both parameters, inlet air
temperatures and feed rate, should be ranging from 110 to 135°C and from 18 to 27
ml/min, respectively. In addition, the lower TBARS values were obtained when the
temperatures were set between 110 to 130°C and feed rates of 18 to 27 ml/min, as shown
in Figure 1b.
Browning of powdered egg as affected by temperatures and feed rates of spraying
is shown in Figure 1c. The temperatures ranged from 150-160°C and feed rates from 4 to
12 ml/min provided lighter color of egg powder.
Figure 1. Response surface plots of output variables of the spray-drying
process as affected by inlet temperatures and feed rates; (a) water activity,
(b) TBARS values, and (c) L values.
In this experiment, lipid oxidation was considered as the major quality factor of
the product. Thus, water activity and TBARS values of powdered egg were selected for
the main output variables for determining the optimal conditions of spray-drying process.
The relationship between the parameters and output variables were exhibited by the
equations shown in table 2.
Table 2. The equations of the output variables*
z = 0.709 - (4.185*10-3)x + (7.899*10-3)y
z = 0.243 + (5.604*10-5)x2 – (1.993*10-4)xy
z = 87.848 + (2.599*10-4)x2 – (1.014*10-3)xy
* The parameters were inlet air temperatures and feed rates; x = temperatures of inlet
air, y = feed rates, and z = output variables.
The inlet temperatures from 110 to 135°C and feed rate from 18 to 27 ml/min
were used for calculation. It was found that the optimal conditions for spray-drying of
whole egg fluid regarding to aw, browning color, and TBARS values were at the inlet
temperature of 135°C and feed rate of 27 ml/min.
The spray-drying parameters, inlet air temperature and feed rate, affected aw,
TBARS values, and browning of whole egg powder. Increasing of temperatures of inlet
air led to the decrease of aw, but increase in TBARS and L values were observed.
Increasing of feed rate caused the increasing of aw, but decreases in values and TBARS
values were observed. The optimal conditions for spray-drying of whole egg were at the
inlet temperature of 135°C and feed rate of 27 ml/min.
This work was supported by Suranaree University of Technology, Nakhon
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