Microsoft Word - 10 Avramiuc.doc

Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava
Volume XI, Issue 2 – 2012

THE INFLUENCE OF HYPOTHERMIC SHOCKS AND ADDITIONS DURING

PROCESSING, ON SOME YOGHURT FEATURES

*Marcel AVRAMIUC1

1Ştefan cel Mare University of Suceava, Faculty of Food Engineering, 13

Universităţii Street, 720229, Suceava, Romania,
e-mail: 1avramiucm@fia.usv.ro

*Corresponding author
Received 25 March 2012, accepted 12 May 2012

Abstract: In this work there was searched the influence of some hypothermic shocks and compound
admixtures, during yoghurt processing, on some yogurt features (pH, titratable acidity and curd
aspect). The biological material used in this work was represented by cow milk, inoculated with a
starter culture of thermophile lactic bacteria, including two different species: Streptococcus
termophilus and Lactobacillus bulgaricus. The experiments during yoghurt processing have consisted
in subjecting of samples to hypothermic shocks, on the one hand, and introducing of some admixtures
(starch or gelatin), in certain proportions, on the other hand, to see the influence of these experiments
on the evolution of pH, titratable acidity and quality characteristics of yoghur curd particles. The
application of hypothermic shocks in the early period of thermostating has determined the decrease of
fermentation activity of lactic bacteria (expressed by reduction of titratable acidity values) and has
made the coagulation process of milk to be blocked. The later applied hypothermic shock, the lower
effect on titratable acidity and coagulation process was. The addition of gelatine or starch during
yoghurt processing has influenced, indirectly, the fermentation activity of lactic bacteria. The gelatin
addition has led to the increase of titratable acidity values, comparing to blank. The addition of
gelatine or starch has not rushed the milk coagulation during yoghurt processing. Compared to the
control, in samples with admixtures the curd formation was slower, especially in those ones with
starch addition.

Keywords: yoghurt, hypothermic shocks, titratable acidity, pH, starch, gelatin.

1. Introduction

In order to avert food unbalances caused
by various deficiency states, last time some
nourishing substances are introduced
within foods, being an efficient way to
ensure an optimum healthy state of people
(1, 2, 3).
The admixtures of active biological
compounds within products poor in
nutritional substances is the method to get
fortifiated foods, having as result the
ensurance of a body maximum protection
(4, 5).
In need, the dairy products can be
supplemented with liposoluble provitamins

/ vitamins (A and/or D), with hydrosoluble
vitamine (niacine, tiamine, riboflavin,

ascorbic acid) or with biominerals, such as:
iron, iodine, fluor etc. (6, 7).
Some works tried to evidence the effect of
certain admixtures on biochemical
processes, having, indirectly, in view the
changes occured within transformations of
carbohydrates and proteins made by lactic
bacteria (8).
In this work there was searched the
influence of some hypothermic shocks and
admixtures of starch or gelatin, during
yoghurt processing, on some yogurt

Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava
Volume XI, Issue 2 – 2012

features (pH, titratable acidity and curd
aspect).

2. Experimental

The biological material used in this work,
was represented by cow milk, whose
biochemical features are rendered below:
- pH: 6.90
- acidity (Törner degrees): 20T
- fats: 1.99%
- proteins: 3.50%
- lactose: 4.40%
- dry matter: 9.85%
- minerals: 0.08%
The milk was inoculated with a starter
culture of thermophile lactic bacteria, used
for direct inoculation within the tub for
yoghurt. The starter culture (a fine
liofilisated powder) has included two lactic
bacteria different species: Streptococcus
termophilus and Lactobacillus bulgaricus.
The thermostating temperature was 43C
during 5 hours, and the inocul dose was
5UA/100 L.
The milk was conditioned with powder
milk (20 g/L) and pasteurised 20-30
minutes at 90○C. For some work variants
there were used only milk or milk with
different admixtures.
The experiments during yoghurt
processing have consisted in subjecting of
samples to hypothermic shocks, on the one
hand, and introducing of some admixtures
(starch or gelatin), in certain proportions,
on the other hand, to see the influence of
these experiments on the evolution of pH,
titratable acidity and quality characteristics
of curd particles of yoghurt.
Thermal shocks have been carried out by
subtracting fast of temperature milk sowed
and thermostated after certain time
intervals, in order to achieve in the end
t=20○C. Samples were kept in the freezer
for 10 minutes, then in the refrigerator for
5 minutes.
Thermal shocks have been performed
after: 30, 90, 150 and 210 of thermostating

minutes at temperature 43○C, and
determinations of above mentioned
indices, have been carried out hour by hour
during yoghurt processing.
The percentage of admixtures used are
rendered below:

Table 1
The percentage of admixtures

Admixtures

Starch % 0.5 1.5 2.5
Gelatin % 0.5 1.5 2.5

The samples with admixtures for trials are
played in the table no. 2:

Table 2
The samples with admixtures for trials

The determination of the titratable acidity,
expressed in Thőrner degree (○T), was
made according to AOAC standard (9), and
the pH values were estimated according to
STAS 8201/82 (10).
As seen in the table 1, in blank (P1) pH
values fell from 6.6 (after first time
keeping in the oven), to pH 4.6 (after 5
hours) - the difference being 2 pH units.
The acidity of milk (sowed with starter
culture) after the first thermostating hour
was 25○T, and in the second hour this
index has grown very little (with only
4○T). Visible changes occurred between 2
hour (29○T) and 3 hours of termostating
process (56○T) – an extra of 27○T,
respectively between 4 hour (61○T) and the
5th termostating hour (82○T) - that an
increase by 21○T. In blank, between the
initial and the final titratable acidity value
reveals a difference of 57○T.

Admixture Sample Starch
(%)

Gelatin
(%)

P1 - -
P2 0.5 -
P3 1.5 -
P4 2.5 -
P5 - 0.5
P6 - 1.5

P7 - 2.5

Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava
Volume XI, Issue 2 – 2012

Table 3

Values of pH and titratable acidity of yogurt samples, subjected to thermal shocks

In sample P2, pH values fell from pH 6.56,
after the first thermostating hour, to pH
6.15 (after 5 hours) – a more pronounced
decrease being registered from 3 to 5 hours
of processing (0.27 pH units). As to
titratable acidity, the growth of this index
was higher between the 3rd and the 5th
thermostating time (5○T) compared with
the interval 1-3 hours (3.3○T).
Compared with the blank, in sample P2,
which suffered thermic shock after 30
minutes of thermostating, it can see that
the hypothermic impact (suffered in that
time), was much felt by the starter bacteria,
whose enzymatic activity has been
drastically reduced, manifested by growth,
in the end, of the titratable acidity with
only 8.3○T.
Sample P3, which underwent hypothermic
shock after 90 minutes of thermostating,
recorded values very close to those of the
sample P2, in terms of pH and titratable
acidity.
Thus, the pH values fell from pH 6.47,
after the first thermostating hour, to pH 6.2
(after 5 hours) – a more pronounced

decrease being registered from 3 to 5 hours
of processing (0.25 pH units).
In sample P3, the growth of the titratable
acidity was higher between the 3rd and the
5th thermostating time (5○T) compared
with the interval 1-3 hours (2.5○T).
When the hypothermic shock has been
applied after 150 minutes of termostating
(sample P4), the pH value has decreased,
in the end, with 1.60 pH units; a more
pronounced reduction being in the range of
1 to 3 hours (0.9 pH units beside 0,7 pH
for range of 3 to 5 hours).
In P4 sample, the titratable acidity has
increased from 25.2○T, after the first time,
at 72○T, after 5 hours, that is with 46.8○T.
In this case, the biggest increase of this
index was in the range of 1 to 3 hours of
thermostating (with 28.2○T).
Sample P5 underwent hypothermic shock
after 210 minutes of thermostating. In this
sample, pH values has decreased, in the
end, with 1.7 pH units, a more pronounced
reduction being in the range of 1 to 3 hours
(0.9 pH units beside 0.8 pH for range of 3
to 5 hours).

The sample number and range of
application of thermal shock from
the start of thermostating process

Analyses made
Thermostating duration

1 h 2 h 3 h 4 h 5 h

P1 (blank)

P2 (hypothermic shock after 30
thermostating minutes)

P3 (hypothermic shock after 90
thermostating minutes)

P4 (hypothermic shock after 150
thermostating minutes)

P5 (hypothermic shock after 210
thermostating minutes)

Acidity (T)
pH

Acidity (T)

6.60 6.48 5.65 4.80 4.60

25 29 56 61 82
6.56 6.51 6.42 6.39 6.15

22.0 23.5 25.3 26.5 30.3

6.47 6.40 6.35 6.40 6.20

22.5 23.5 25.0 29.5 30.0

6.50 6.48 5.60 5.20 4.90
25.2 35.5 53.4 58.2 72

6.50 6.45 5.60 5.10 4.80

25.5 34 56 65 78

Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava
Volume XI, Issue 2 – 2012

Table 4
Noting of curd is played as follows:

In the same sample, the titratable acidity
has increased from 25.5○T, after the first
time, at 78○T, after 5 hours, that is with
52.5○T. In this last case, the biggest
increase in this index was in the range of 1
to 3 hours of termostating (with 30.5○T).
In the table 5 is reproduced the evolution
of milk coagulation under hypothermic
shocks.

Table 5
The comparative evolution of milk coagulation during yoghurt processing, in terms of thermal

shocks application

The coagulation evolution of milk sowed with starters cultures,
during thermostating period

The sample number and range of
application of thermal shock from
the start of thermostating process

1 h 2 h 3 h 4 h 5 h
P1 (blank) 0 + + + + + + + + + + +

P2 (hypothermic shock after 30
thermostating minutes)

0 0 0 0 0

P3 (hypothermic shock after 90
thermostating minutes)

0 +  +  + +

P4 (hypothermic shock after 150
thermostating minutes)

0 + + + + + + + +

P5 (hypothermic shock after 210
thermostating minutes)

0 + + + + + + + + + +

As seen in table 2, the milk coagulation
during yoghurt processing had a different
evolution in samples subjected to
hypothermic shocks compared to blank. In
blank (P1), the curd was: formed (after 2
and 3 hours), well-formed (after 4 hours)
and very well-formed (after 5 hours). If in
the sample P2 the curd has not appeared at
all during yoghurt processing, in the other
samples the curd had a different evolution,
depending on the application of
hypothermic shock. Thus, in P3 after 2 and
3 hours the curd has been very weak, and
after 4 and 5 hours its aspect was of curd
which begins to form.
In the sample P4, the curd was formed
after 2 hours, and it was maintained in this
form up to the end of process (without
being well-formed).
In the sample P5, the curd was formed
after 2 hours, then it bacame very well-

formed after 4 hours, and it was
maintained in this form up to the end of
process.
Application of hypothermic shock in the
early period of thermostating (the sample
P2) has made the coagulation process of
milk to be blocked. The later applied
hypothermic shock, the lower effect on
coagulation process was (samples 4 and 5).
The table 3 reproduces pH and acidity
values of yoghurt samples, with addition of
starch or gelatin.
According to the table 3, in blank (P1) pH
values fell from 6.6 (after first hour) to 4.6
(after 5 hours of thermostating). The
tiratable acidity of blank registered a
difference of 57○T between the initial
value (25○T) and the final value (82○T) of
this index.

0 Negative

+  Very weak curd
+ Curd begins to form
+ + Curd formed
+ + + Well-formed curd
+ + + + Very well-formed curd

Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava
Volume XI, Issue 2 – 2012

Table 3
Biochemical index values of yoghurt samples, with addition of starch and gelatin, in certain proportions

In the sample P2, (with 0.5% starch) pH
values fell from pH 6.7, after the first
thermostating hour, to pH 5.06 (after 5
hours). As to titratable acidity, the growth
of this index was 45.5○T, and its final
value (in the end of process) was 70○T.
In the sample P3 (with 1.5% starch) the pH
values fell from pH 6.60, after the first
thermostating hour, to pH 4.7 (after 5
hours). The titratable acidity has grown
from 25 to 78○T (in the end of process),
that is a difference of 53○T.
The sample P4 (with 2.5% starch) has
registered a decrease of pH values from pH
6.72, after the first thermostating hour, to
pH 4.69 (after 5 hours). The titratable
acidity has grown from 24.6 to 79○T (in
the end of process), that is a difference of
54.4○T.
In the sample P5 (with 0.5% gelatin) pH
values fell from pH 6.68, after the first
thermostating hour, to pH 4.45 (after 5
hours). As to titratable acidity, the growth
of this index was 65○T - the final value of
this index (after 5 hour of thermostating)
being 90○T.
The sample P6 (with 1.5% gelatin) has
registered a decrease of pH values from pH

6.50, after the first thermostating hour, to
pH 4.52 (after 5 hours). The titratable
acidity has grown from 30.4 to 88○T (in
the end of process), that is a difference of
58.6○T.
In the sample P6 (with 2.5% gelatin) pH
values fell from pH 6.48, after the first
thermostating hour, to pH 4.40 (after 5
hours). As to titratable acidity, the growth
of this index was 60.4○T - the final value
of this index (after 5 hour of
thermostating) being 93○T.
Comparing the values of the indexes in tab.
3, it can see that in the case of samples
with gelatin admixture pH values were
lower, and the titratable acidity higher than
blank. Along with the increasing of gelatin
amount added, the titratable acidity has
grown too. In all samples with starch
added, the titratable acidity value was less
then blank.
It is known that pH and titratable acidity
are biochemical indices expressing,
indirectly, the fermentation activity of
lactic bacteria. Since no starch or gelatin
can be used directly as a source of carbon
and energy by lactic bacteria cultures, this
increasing of the fermentation activity (in

Thermostating duration

The sample number and
the compound added

Analyses made

1 h 2 h 3 h 4 h 5 h
pH 6.60 6.48 5.65 4.80 4.60 P1 (blank)

Acidity (○T) 25 29 56 61 82
pH 6.70 6.48 6.01 5.15 5.06 P2 (0.5% starch)

Acidity (○T) 24.5 30 404 57 70
pH 6.60 6.50 5.50 4.95 4.70 P3 (1.5% starch)

Acidity (○T) 25 31.2 57 59.4 78
pH 6.72 6.50 5.54 4.93 4.69 P4 (2.5% starch)

Acidity (○T) 24.6 31 54 60.4 79
pH 6.68 6.42 5.48 4.89 4.45 P5 (0.5% gelatin)

Acidity (○T) 25 34.8 56.2 60 90
pH 6.50 6.34 5.89 5.10 4.52 P6 (1.5% gelatin)

Acidity (○T) 30.4 39.8 49.6 58.4 88
pH 6.48 6.35 5.52 5.06 4.40 P7 (2.5% gelatin)

Acidity (○T) 32.6 38.8 54.2 58 93

Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava
Volume XI, Issue 2 – 2012

the case of gelatin addition) could be
explained by the role of oxygen barrier that
plays the gelatin inside emulsions (7).
Limiting or blocking access of oxygen
within emulsion (milk) mass, favors the
fermentation activity of lactic cultures.
In the table 4 is rendered the evolution of
milk coagulation during yoghurt
processing.
As seen in table 4, the milk coagulation
during yoghurt processing had a different
evolution. In blank (P1), the curd was
formed (after 2 and 3 hours), well-formed
(after 4 hours) and very well-formed (after
5 hours).

In the sample P2 (0.5% starch) the curd
was very weak after 2 and 3 hours, it began
to form after 4 hours and is formed in the
end of process.
At sample P3 (1.5% starch), the curd was
very weak after 2 and 3 hours, it began to
form after 4 hours, an was formed after 5
hours (in the end).
The curd of sample P4 (2.5% starch) was
very weak after 2 and 3 hours, it began to
form after 4 hours, and was wel-formed in
the end of process.

Table 4
The comparative evolution of milk coagulation during yoghurt processing, in terms

of some compound additions
The coagulation evolution of milk sowed with starters

cultures, during thermostating period
The sample number
and the compound

added 1 h 2 h 3 h 4 h 5 h
P1 (blank) 0 + + + + + + + + + + +
P2 (0.5% starch) 0 +  +  + + +

P3 (1.5% starch) 0 +  +  + + +

P4 (2.5% starch) 0 +  +  + + + +

P5 (0.5% gelatin) 0 +  + + + + + +

P6 (1.5% gelatin) 0 +  + + + + + + +

P7 (2.5% gelatin) 0 + + + + + + + +

Table 5

Noting of curd is played as follows:
0 Negative
+  Very weak curd
+ Curd begins to form
+ + Curd formed
+ + + Well-formed curd
+ + + + Very well-formed curd

At sample P5 (0.5% gelatin), the curd was
very weak after 2 hours, it began to form
after 3 hours, it bacame formed after 4
hours, and well-formed after 5 hours (in
the end).
In the sample P6 (1.5% gelatin) the curd
was very weak after 2 hours, it began to
form after 3 hours, was formed after 4

hours, and very well-formed in the end of
process.
The curd of sample P7 (2.5% gelatin)
began to form after 2 and 3 hours, it
became formed after 4 hours, and very
well-formed in the end of process.
Analysing the data in the table 4, it seems
the addition of gelatine or starch has not

Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava
Volume XI, Issue 2 – 2012

rushed the milk coagulation process during
yoghurt processing. Compared to the
control, in samples with admixtures the
curd formation was slower, especially on
samples with starch addition.

4. Conclusions

During yoghurt processing, the application
of some hypothermic shocks and the
introduction of some compounds has
influenced the evolution of acidity and the
milk coagulatin process.
Application of hypothermic shocks in the
early period of thermostating has
determined the decrease of fermentation
activity of lactic bacteria (expressed by
reduction of titratable acidity values) and
has made the coagulation process of milk
to be blocked. The later applied
hypothermic shock, the lower effect on
titratable acidity and coagulation process
was.
The addition of gelatine or starch during
yoghurt processing has influenced,
indirectly, the fermentation activity of
lactic bacteria. The gelatin addition has led
to the increase of titratable acidity values,
comparing to blank.
The addition of gelatine or starch has not
rushed the milk coagulation during yoghurt
processing. Compared to the control, in
samples with admixtures the curd
formation was slower, especially in those
ones with starch addition.

5. References

[1].JUILLET M.T., BORNET F., 1998 – Assurer
une alimentation équilibrée popur maintenir la
santé. Ind. Alim. Agric., 115, 12, 19
[2] MINCU I. et.al., 1989 – Orientări actuale în
nutriţie. Ed. Medicală, Bucureşti
[3] SEGAL B. et al., 1987 – Metode moderne
privind îmbogăţirea valorii nutritive a produselor
alimentare. Ed. Ceres, Bucureşti
[4] NICOL M., 1995 – Vitamines antioxydantés et
bêta-caroténe: activités prevéentives en pathologie
humaine. Réunion commentée, Mèd. et Nutr., 31, 1,
41-46
[5] NAGY K.,1999 – The role of Food
Fortification in Combating Micronutrient
Deficiences. F Hoffmann-La Roche Basle-
Switzerland
[6] BANU C. et al.., 2003 – Procesarea materiilor
prime alimentare şi pierderile de substanţe biologic
active. Ed. „TEHNICA” UTM, Chişinău, 138
[7] SEGAL RODICA, 1999 – Alimente fortifiate, in
Alimente funcţionale de G.M. Costin şi Rodica
Segal (edit.) et.al.,1999, Ed. Academica, Galaţi,
308
[8] AVRAMIUC M., LEAHU A., 2009 – The
influence of some metabolits addition on
fermentation process, during butter milk
manufacturing. Journal of Agroalimentary
Processes and Technologies, Timişoara, vol. XV,
Nr. 1, 88-93
[9] CUNNIFF P. (Ed), 1995 – Official methods of
analysis of AOAC International (16th ed., vol 1,2),
Association of Officinal Analytical Chemists
International, Arlington, VA.
[10] COSTIN G.M. SI SEGAL R. (edit.) et..al.,
2003 – Ştiinţa şi ingineria fabricării brânzeturilor.
Ed. Academica, Galaţi, 502, 503, 504, 510.