76 
 

Journal homepage: www.fia.usv.ro/fiajournal 
Journal of Faculty of Food Engineering,  

Ştefan cel Mare University of Suceava, Romania  
Volume XV, Issue 1 - 2016, pag. 76 - 83 

 

 

THE USE OF GLASS TRANSITION TEMPERATURE IN FORECASTING WHEY 

POWDER STORAGE STABILITY OBTAINED BY ELECTRO-SPARK 

TREATMENT 
 

*Оksana KOCHUBEI-LYTVYNENKO1, Vyacheslav MYKHAILYK2, Anatoliy UKRAINETS1 
 

1NationalUniversity of Food Technologies, 68 Volodymyrska str., Kyiv, Ukraine, okolit@email.ua 
2Institute of Engineering Thermal Physics, National Academy of Sciences of Ukraine, 2 Acad. Bulakhovskii str., 

Kyiv, Ukraine, mhlk45@gmail.com 
*Corresponding author  

Received Februay 18th 2016, accepted March 28th 2016 
 

 
Abstract: This study investigated the behavior during storage of dry whey obtained using different approaches 
that prevent caking (by adding silicon dioxide, electro-spark treatment of whey). Forecasting the stability of 
quality whey powder was carried out based on a glass transition temperature.The glass transition temperature 
of whey powder was measured by differential scanning calorimetry.We showed that the highest glass transition 
temperature (+18.5 °С) and,subsequently, the smallest difference between product temperatures and glass 
transition temperature were discovered in dry whey, obtained with the use of electro-spark treatment, which 
proved to be stable during storage.We have found that the other samples of dry whey under normative storing 
conditions (from 0 till 20 °С) are predominantly in rubbery state, which can  influence negatively the  stability of 
the product during storage. Based on the glass transition temperature we determined that electro-spark 
treatment used in the technology of whey powder allowed reaching anti-caking effect due to physico-chemical 
processes resulting from electro-spark charges. This was proved by calculating the stickiness and caking 
sensibility index and the degree of caking (to 2 %). It was experimentally proved that the dry milk whey 
produced with electro-spark treatment differed positively from other samples by absence of non-fermentative 
darkening.Whey powder produced from whey treated with electro-spark charges was characterized by the 
highest degree of whiteness, which did not significantly change in 8 month storage. 

 
Keywords: wheypowder, electro-spark treatment, glass transition temperature, caking, stickiness and 
caking sensibility index. 
 
 
1. Introduction 

 
Dry milk whey belongs to amorphous 
metastable products, which is very 
sensitive to temperature and humidity 
changes. Spoiling of low humidity 
products during storage is determined by 
chemical, biochemical or/and physical 
changes, including migration and loss of 
humidity which can cause caking, 
fermentative and non-fermentative 
reactions displayed by product darkening.  
Conditions of outer environment 
(temperature, moisture content) have big 
influence upon these processes, as well as 

product structure, active acidity, water 
activity index etc.  
In order to increase quality, avoid spoiling 
of food products and to increase their shelf 
life, various technological measures are 
used, as well as nontraditional treatment 
measures, processing methods and storage 
techniques. At the same time for long shelf 
life products, including dry whey 
concentrate, important issue is the choice 
of qualities and characteristics used for 
objective and reliable forecasting of quality 
index changes during storage.  
In a range of works [1-5] correlation was 
proved between some qualities of dry 

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Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefancel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Оksana KOCHUBEI-LYTVYNENKO, VyacheslavMYKHAILYK, Anatoliy UKRAINETS, The use of glass transition 
temperature in forecasting whey powder storage stability, obtained by electro-spark treatment, Food and Environment 
Safety, Volume XV, Issue 1 – 2016, pag. 76 – 83 
 77 

products (such as stickiness, caking) and 
glass transition – phase transition of 
separate nature, particular to amorphous 
material.  
The process of glass transition is a process 
of material transition from glass-like to 
rubber-like state and vice versa which is 
accompanied by changes in its 
thermodynamic and mechanical qualities, 
molecular mobility and dielectric 
penetrability[6]. The range of temperatures 
at which this transition is observed is 
called the glass transition temperature (Tg). 
The concept of glass transition together 
with the concept of water activity is lately 
widely used to forecast stability of food 
products under drying and storage[7]. 
It is considered that stability of 
organoleptic, chemical and 
physicochemical qualities of dried food 
products depends on storage temperatures. 
At temperatures higher than glass 
transition temperature may occur 
oxidation, crystallization and 
recrystallization processes, and increase in 
adhesive qualities, because is increasing in 
molecular mobility and lowering viscosity 
of the material. This in turn leads to 
changes in chemical and physical state, 
sticking of particles on the solid surface 
and caking of the product. The speed of 
such changes is determined by the 
difference in product temperatures (Т) and 
Tg [2, 7, 8]. 
Itisknownthatthelowerthedifferencebetwee
nproductstoragetemperatureandglass 
transition temperature, thebetterisitsstorage 
[2, 3, 6]. 
Humidity content of the product has a 
decisiveinfluenceupontheglass transition 
temperature [8, 9, 14, 18, 22]. The change 
in chemical content, phase state of sugars 
and biopolymers (casein, whey proteins) 
has its influence upon dependence of 
Tgfrom product humidity content [13-22].  
Scientific sources predominantly pay 
attention to glass transition temperature of 
vegetative origin products, separate 

components (including various 
carbohydrates) and model samples of dry 
products. At the same time, not much data 
is available on multicomponent products, 
produced in industrial conditions with the 
use of modern technological approaches, 
including demineralization of whey, use of 
electrophysical treatment procedures and 
anti-caking agents. However, this data is 
necessary to determine or prove storage 
regimes of dry products and to forecast 
stability of their quality indexes.  
Theaimoftheworkwastodetermineglass 
transition temperature ofdrymilkwhey, 
obtained with the use of various 
approaches that prevent caking (adding 
silicon dioxide, electro-spark treatment of 
whey); 
tostudythebehaviorofexperimentalsamples
duringpackaging, 
transportationandstoragebyparametersdiap
asonchange [T – Tg]. 

 
2. Materials and Methods 

 
2.1. Objects of research.  

Demineralizedwheypowder(WPD)
wasderivedbydemineralizationofcheesewh
eyatnanofilterutility(GEA, Denmark), 
thickening(end up with mass fraction of 
milk solidsto 50-52 %), 
coolingofthethickenedmilkwheyandcrystall
izationoflactose (10-12 hours, under 15 °С) 
and further drying at spraying drier 
(Vzduchotorg, Slovak Republic). 

Whey powder enriched with particles 
of magnesium and manganese 
(WPEPMgMn)wasobtainedbytheabovementi
onedscheme,butdemineralized whey 
wastreatedatexperimentalelectro-
sparktechnologicalinstallationbeforethicke
ning.Thelatter consisted of charge impulse 
generator, control panel, running charge 
chamber, measuring and supplementary 
tools[10]. Electro-spark treatment was 
conducted under such conditions of charge 
contour: recharge condenser voltage – (75 
± 5) V; condenser volume – 100 uF; 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefancel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Оksana KOCHUBEI-LYTVYNENKO, VyacheslavMYKHAILYK, Anatoliy UKRAINETS, The use of glass transition 
temperature in forecasting whey powder storage stability, obtained by electro-spark treatment, Food and Environment 
Safety, Volume XV, Issue 1 – 2016, pag. 76 – 83 
 78 

resistance of granules layer in charge 
chamber – 0.15–1.5 Om; interval between 
metal granules – to 0,1 mm; impulse 
frequency – 0.2–2.0 kHz; exposition – 1 
min for magnesium electrode system; 0.5 
min – for manganese electrode system. In 
result of volumetric electro-spark 
dispersion of metal granules (Mg and Mn), 

whey was enriched by these components 
(Table 1).  
Content of Mg and Mn in whey samples 
was determined at atomic-absorption 
spectrometer ААS1N (Carl-Zeiss Jena, 
Germany), equipped with burner for 
acetylene-air flame and lamps with hollow 
cathode for magnesium and manganese.  

 
 

Table 1 
Content of magnesium and manganese inwheypowders 

 
Whey powders ContentMg, g/kg ContentMn, mg/kg 

WPD 0.94±0.03 1.1±0.04 
WPEPMgMn 2.9±0.15 12.9±0.5 

Demineralized whey powder with anti-
caking agent (WPDACA) 1.0% of anti-
caking agent was added to demineralized 
whey powder and thoroughly mixed. 
Silicon oxide SiO2 (E-551 Silicon dioxide 
amorphous) was used as an anti-caking 
agent.  

 
2.2.  Chemical and physical analysis 

 
Glass transition temperatures and heat 
capacity changes (ΔCp) were determined 
using differential scanning 
microcalorimeter (DSC-2M) made at 
Special design office of biological 
instrument making in Pushchino (Russia) 
and equipped with a ThermCap data 
acquisition and processing program written 
in the Delphi programming language. 
Micro calorimeter temperature scales were 
graded by to two benchmark points: -95.0 
°С (melting temperature of chemically 

pure toluene) and 0 °С (melting 

temperature of water after double 
distillation). Cooling of calorimeter block 
was performed with the use of liquid 
nitrogen. Accuracy of temperatures 
measurement was not worse than ±0.1 °С. 

The samples were hermetically canned in 
aluminum containers. Weighting was 
performed at microanalytical scales VLM-
1 with accuracy ±0.01 mg. Overall content 
of water in samples was determined after 
measurements by dehydration till constant 
mass in the drying box at 104-105 °С. 
In order to avoid artifacts connected to 
humidity condensation in calorimeter 
chambers, measurement block was filled 
with dried gas-like helium, which flow was 
controlled during measurements.  
Samples were cooled at –50 °C at scanning 
rate 16 К/min. Temperature intervals 

(Tg), beginning temperatures 
s

gT  and end 
temperatures of glass transition 

f
gT  were 

determined by DSC-curves, obtained under 
heating of samples at scanning rate 16 
К/min from –50 till +35 °C. Typical DSC 
heating curve is presented at fig.1. Tg was 
determined as Tg/2. The change in heat 
capacity under glass transition Cp was 
obtained by the difference in heat capacity 

at 
f

gT and
s

gT . Each sample had undergone 
at least three measurements.

 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefancel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Оksana KOCHUBEI-LYTVYNENKO, VyacheslavMYKHAILYK, Anatoliy UKRAINETS, The use of glass transition 
temperature in forecasting whey powder storage stability, obtained by electro-spark treatment, Food and Environment 
Safety, Volume XV, Issue 1 – 2016, pag. 76 – 83 
 79 

 
Fig. 1 Typical DSC heating curveforwhey powder showing the glass transition 

 
 

The degree of caking was measured using 
the method described by Pisecky [11]. In 
the beginning amount of whey power (5 g) 
was kept in desiccators under artificially 
created conditions of high humidity (above 
80 %) until the mass increase stopped. 
Afterwards samples were dried in drying 
box during 1 hour at 104±2 °С. After 
cooling in a desiccators, the sample was 
weighed, quickly transferred to a stainless 
steel sieve (250 µm), and shaken for 5 
minutes in a shaking apparatus. The 
powder that passed through the sieve was 
weighed, and the caking index was 
determined by the equation 1. 

100
1

21 



M

MM
СЗ   

    (1) 
whereМ1is the total mass of powder (g) 
and М2is the mass of fines that passed 
through the sieve (g). 

Ability of dry product particles to 
stickiness and/or caking during treatment 
and storage was forecasted under a 
stickiness and caking sensitivity index 
(SCSI). SCSI (in diapason from 0 to 10) 
was determined by equation 2 according to 
parameters changes diapason [T – Tg] (T – 
temperature of dry product) and ΔCp [3].  
SCSI = Number of points [T – Tg] + 
Number of points [ΔCp],   
 (2) 

 
whereTg is the glass transition 
temperature, С; T – dry product 
temperature (at the exit from drier, in the 
dry powder batch mixer and under 
storage), С; ΔCp – change in heat 
capacity, J/(g∙К). 
This index simultaneously integrates the 
values of [T – Tg] (ranging between 0 and 
5) and ΔCp (ranging between 0 and 5) 
(Tab. 2) [3]. 

 
 
 
 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefancel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Оksana KOCHUBEI-LYTVYNENKO, VyacheslavMYKHAILYK, Anatoliy UKRAINETS, The use of glass transition 
temperature in forecasting whey powder storage stability, obtained by electro-spark treatment, Food and Environment 
Safety, Volume XV, Issue 1 – 2016, pag. 76 – 83 
 80 

Table 2 
Calculation of stickiness and caking sensitivity index [3] 

 
T – Tg, 
С 

ΔCp, 
J/(g∙К) Number of points 

[T – Tg]≤5 ΔCp<0.1 0 
5<[T – Tg]≤10 0.1≤ ΔCp<0.2 1 

10<[T – Tg]≤15 0.2≤ ΔCp<0.3 2 
15<[T – Tg] ≤20 0.3≤ ΔCp<0.4 3 
20<[T – Tg]≤30 0.4≤ ΔCp<0.5 4 

30<[T – Tg] 0.5≤ ΔCp 5 
 

Non-fermentative darkening of dry milk 
whey was determined by the change of 
product whiteness during storage. 
Whiteness of the product was estimated in 
relative points at Blik-P3 (Russia) 
instrument for measurement of directed 
zonal reflection index and determining 
whiteness. 

3. Results and discussion 
 
For research objects DSCcurves of heating 
were determined (fig.2), according to 
which characteristic temperatures of glass 
transition were found out (Table 3). 

 

 
Fig.2 DSC heating curvesforwheypowder: 1 – WPD, 2 – WPEPMgMn, 3 – WPDАСА. 

 
 
Results obtained showed the difference in 
studied samples by glass transition 
temperatures. The control sample of 
demineralized whey powder had the lowest 
Tg level. Addition of silicon dioxide as an 
anti-caking agent to WPD leads to 

increaseglass transition temperature on 10 
С. It was observed highest Тg value for 
whey powder enriched with magnesium 
and manganese particles. 
Significant Тg grow in whey powder, 

produced with the use of electro-spark 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefancel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Оksana KOCHUBEI-LYTVYNENKO, VyacheslavMYKHAILYK, Anatoliy UKRAINETS, The use of glass transition 
temperature in forecasting whey powder storage stability, obtained by electro-spark treatment, Food and Environment 
Safety, Volume XV, Issue 1 – 2016, pag. 76 – 83 
 81 

treatment, and most likely is explained by 
physicochemical processes taking place in 
whey components, as a result, of electro-
spark charge. Among them: accumulation 
of magnesium and manganese particles in 
colloidal form in case of their transition 

from electrodes to solution; their 
interaction with water and whey 
components (including proteins and thus 
increasing its molecular mass); transition 
of lactose and creation of its derivatives 
(lactulose, lactobionic acid) [12]. 

 
Table 3 

Wheypowdersampleshumiditycapacityandtemperaturesofglasstransition 
 

Sample 
Moisture content, 

g/gdrywhey 
s

gT , 
C 

f
gT , 
C 

Glass transition temperature, 
Tg, C 

WPD (control)  0.044 −18.0±0.2 +12.0±0.2 −3.0±0.2 
WPEPMgMn 0.031 +10.0±0.2 +27.0±0.2 +18.5±0.2 
WPDАСА 0.034 −6.0±0.2 +19.0±0.2 +6.8±0.2 

 
The conduct of researched whey powder 
samples during packaging, transportation, 
mixing with other components (sticking of 
particles to hard surfaces) and storage 
(caking) was forecasted by the change in 
index diapasons [T – Tg] and ΔCp, 
established by DSC-curves. The SCSI 
value calculated from equation 2. It is 
known that SCSI allows to forecast the dry 
product behavior during drying, 
transportation and storage, from the most 
favorable case (SCSI ≤ 4: no stickiness 

and/or no caking) to the most unfavorable 
(SCSI ≥ 6: high to very high stickiness or 

caking hazard) [3].  
For measurements with the aim of 
forecasting product behavior during 
packaging, transportation (stickiness) and 
storage (caking), such temperatures were 
taken for the dry product (Т): on the exit 
from dryer – +30 С; storage – +20 С. 
Calculated results are presented in Table 4. 

 
Table 4 

Wheypowderbehaviorduringpackaging, transportationandstorage 
as a functionof [T – Tg] andΔCp values 

 

 
The analysis of received values showed 
that the highest ability to caking and high 
stickiness was particular for control sample 
of whey powder. Adding silicon dioxide 
decreased product caking risk, which was 
proved by SCSI and level of caking, 
measured experimentally. 
Based on the glass transition temperature 
measurement and change of specific heat 

capacity, it was determined that including 
electro-spark treatment in technology of 
whey powder allowed reaching anti-caking 
effect due to physicochemical processes 
resulting from electro-spark charges. This 
was proved by stickiness and caking 
sensibility calculation index (SCSI =2) as 
well as experimental data of the degree of 
caking (to 2 %). 

Sample 
 

ΔCp, 

J/(g∙К) 
Stickiness Caking Degree of caking, 

% (experimental 
data) 

[T – Tg], C SCSI 
(calculated 

data) 

[T – Tg], C SCSI 
(calculateddata) 

WPD (control)  0.38 33.0 8 23.0 7 16.4±0.7 
WPEPMgMn 0.23 11.5 4 1.5 1 2.0±0.04 
WPDАСА 0.32 23.2 7 13.2 5 13.4±0.4 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefancel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Оksana KOCHUBEI-LYTVYNENKO, VyacheslavMYKHAILYK, Anatoliy UKRAINETS, The use of glass transition 
temperature in forecasting whey powder storage stability, obtained by electro-spark treatment, Food and Environment 
Safety, Volume XV, Issue 1 – 2016, pag. 76 – 83 
 82 

Research results and SCSI levels, 
calculated on their basis fully correspond 
to observations over research samples in 
the process of storage under 18±2 С 
temperatures and relative humidity not 
more than 80 %.  
It is worth mentioning that besides stability 
to caking of whey powder particles 
produced with the use of electro-spark 
treatment, these samples positively differed 
from other samples by the absence of non-
fermentative darkening.  
Researchsamplesproducedfromthewheytre
atedwithelectro-spark charges was 
characterized by highest degree of 

whiteness, which did not significantly 
lower in 8 months storage (Table 5). Other 
samples suffered from lowering whiteness 
index by 8.8-10.5 conventional units 
depending on the type of 
product.Lossofwhitenesstestifiestheflowof
Maillardreaction, 
whichasknowncannotretardevenunderlowh
umidityunlikeotherbiochemicalprocesses.N
evertheless,its speed decreases by reducing 
the difference between the storage 
temperature andTg[2, 3]. It was observed 
in whey samples prepared using electric 
spark treatment. 

 
Table 5 

Change of whiteness in whey powder research samples during storage 
 

Sample Whey powder whiteness, conventional units, 
in storage 

1 month 6 months 8 months 
WPD 90.6±2.0 83.6±2.3 80.1±1.7 

WPEPMgMn 97.4±1.0 95.7±1.1 95.1±0.8 
WPDАСА 90.9±1.6 85.4±1.0 82.1±1.2 

 
4. Conclusions 
 
This study investigated the behavior during 
storage of dry whey obtained using 
different approaches that prevent caking 
(adding silicon dioxide, electro-spark 
treatment of whey). Forecasting the 
stability of quality whey powder was 
carried out based on a glass transition 
temperature. 
We showed that the highest 
glasstransitiontemperature (+18.5 °С) 
and,subsequently,smallestdifferencebetwee
n product temperatures and glass transition 
temperaturewere discovered in dry whey, 
obtained withtheuseofelectro-
sparktreatment, which proves its stability 
while in storage. 
We found that the other samples of dry 
whey under normative storing terms (from 
0 till 20 °С) are predominantly in rubbery 

state which can negatively influence on 
stability of the product while in storage.  
Based onthe glass transition temperaturewe 
determinedthatincludingelectro-
sparktreatmentintechnologyofwheypowder
allowed reaching anti-caking effect due to 
physicochemical processes resulting from 
electro-spark charges. This was proved by 
calculation stickiness and caking 
sensibility index and thedegreeofcaking(to 
2 %).  
Itwasexperimentallyprovedthat the 
drymilkwheyproducedwithelectro-
sparktreatmentpositivelydifferedfrom other 
samples byabsenceofnon-
fermentativedarkening.  
Whey 
powderproducedfromthewheytreatedwithel
ectro-spark charges was characterized by 
highest degree of whiteness, which did not 
significantly lower in 8 months storage. 
Other samples suffered from lowering 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefancel Mare University - Suceava 
Volume XV, Issue 1  – 2016 

 

 
Оksana KOCHUBEI-LYTVYNENKO, VyacheslavMYKHAILYK, Anatoliy UKRAINETS, The use of glass transition 
temperature in forecasting whey powder storage stability, obtained by electro-spark treatment, Food and Environment 
Safety, Volume XV, Issue 1 – 2016, pag. 76 – 83 
 83 

whiteness index by 8.8-10.5 conventional 
units depending on the type of product. 

 
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