الفهرس 
Material and methodsOnly 14 pages are availabe for public view
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Abstract
SUMMARY AND CONCLUSION
Prevention of raw milk spoilage during storage and
transportation can help to improve and enhance increased milk
production and utilization. The use of hydrogen peroxide as a
milk preservative was recommended by FAO in 1957. The use of H202
must be with high concentrations to prolong the milk keeping
quality which usually leads to deleterious effects in the liquid
phase and the manufactured products. An alternative to preserve
a high milk quality is to activate the naturally occuring
lactoperoxidase system (Lp-system). The IDF in 1988 reported
that the Lp-system is an indigenous antibacterial system in milk
and human saliva and its use in the presevation of raw milk have
been recommended without any health hazards.
Therefore, this investigation was planned to provide some
data on the effect of H202 per se and the Lp-system in the
preservation of raw cows’ and buffaloes’ milk under local
conditions. It was worthwhile also, to evalute the feasibility
of using such milks in making low salt Domiati cheese and
yoghurt.
The investigation was carried out in three part.
PartI: using hydrogen peroxide as a milk preservative
The H202 concentration in milk of some collecting centers
that provide Misr & Food Company was determined. The H202
concentration was followed up during the manufacture of milk.
Also, some factors which affect the use of H202 in preserving
milk were studied. The results can be summarised as follows:
I-The average concentration of H202 in milk of some collecting
points ranged from 262.5 to 597.03 ppm.
2-The average residual H202 in raw milk received by Misr Milk &
Food Company ranged from 2.43 to 18.38 ppm for all collecting
centers of the surveyed gavernorates. The bulk milk from large
farms was free from H202•
3-Milk samples containing 10 ppm H202 or lower produced
pasteurized milk (90°C/15 sec.) free from residual H202• The
higher content of H202 in raw milk produced more residual H202 in
pasteurized milk. In Domiati cheese the residual H202 either in
curd or whey was detected when the milk contains 25 ppm or more.
The percentage of H202 decomposition decreased with increasing
the H202 concentration during heating of milk.
4-The changes of pH were very limited in the low concentrations
(200-350 ppm) when the milk stored at room temperature and the
decomposition of H202 was high. The pH of milk with high levels
of H2
0
2 (400-650 ppm) remained unchanged compared with the
control. The percent of recovery increased as the amount of added
H202 increased.
Under cooling condition of milk storage the H202
decomposition takes place in a low rate.
S-Heating milk containing H202 showed that H202 is less stable at
higher temperatures and the rate of decomposition is accelerated
at higher temperatures. Low levels of H202 added to milk are very
unstable and decompose rapidly.
242 -
6-Addition of H202 to raw milk increased the keeping quality of
milk as evaluating by the bacterial count,titratable acidity and
COB test. The time of storage is dependant on the level of H20,
added. The cows’ milk was found to be more stable than buffaloes’
milk.
7-There was a great reduction in H20, during milk separation, and
the rate of decomposition was affected by the H20, level in the
separated milk.
Part II.Using lactoperoxidase system as a milk preservative.
In this part some trials were carried out in order to attain
the maximum keeping quality of cows’ and buffaloes’ milks, which
was evaluated by bacterial count, titratable acidity and COB
test.
The results were as follws:
I-The thiocyanate content in different kinds of milk varies
greatly. Sheep milk recorded the highest thiocyanate content as
it reached up to 20.63 ppm. cows’, buffaloes’, goats’ milks and
bulk raw mixed recorded 6.1,5.13,4.38 and 3.73 ppm respectively.
2-Three combinations of SCN-:H,O, were used for application in
preservation of cows’ and buffaloes’ milk at ambient temp. These
are 10:7.5,14:30 and 25:15 ppm of SCN-:H20,. The preservation
effect was more conspicuous by employing combination of 25:15
followed by 14:30 and the lowest effect was 10:7.5 ppm of SCN-
:H2
0
2 The keeping quality of cows’ milk was higher than
buffaloes’ milk in all treatments.
3-The effect of second dosing at 4 and 8 h interval showed that
the selection of the 14:30 followed by adding 30 ppm H202 after
4 h is more reseamable for application. The preservation of cows’
and buffaloes’ milk was prolonged to 18 and 16 h successively.
4-The electrophoretic patterns of preserved milk proteins in both
cows’ and buffaloes’ were discussed,
Part III. Utilization of preserved milk in the manufacture of
some dairy products.
This part was undertaken to use cows’ and buffaloes’ milk
treated with H202 (at levels of 200 and 250 ppm respectively) or
treated with Lp-system (14:30 ppm SCN-:H202 ) followed after 4 h
by a second dose of 30 ppm H202 in the manufacture of Domiati
cheese-like and yoghurt,
The results can be summarized as follows:
Section A: Domiati cheese
Seven treatments were done: cheese with 10% salt,5% salt,
Lp-system + 5% salt,H202 + 5% salt, unsalted, Lp-system
(unsalted) and H202 (unsalted).
I-The treatment of milk cheese with the preservatives increased
the coagulation time and yield while it slightly decreased the
curd tension the effect was more pronounced in the treatment with
H202 than Lp-system. Also the effect of salt was discussed.
2-The unsalted cheese was spoiled after the manufacture either
treated or untreated.
3-Treatment of cheese milk with preservatives e.g. Lp-system/H202
or salt increased the moisture content and decreased the acidity
in the resultant cheese.
4-Using Lp-system and H202 treatments have no effect on salt
content of the cheese. This is abvious in salt/water ratio.
Storage of cheese decreased the salt content. Also, the
treatments have no effect on fat content.
S-Treatment of cheese milk with preservatives have no effect on
T.N. content of the resultant cheese but the differences are due
to variations in the moisture and salt contents. The T.N.
decreased gradually during storage.
6-The soluble nitrogen increased gradually during ripening. It
was decreased as the salt content increased. However, decreasing
the salt (5% salt) raised the acidity and inhibit the proteolysis
of protein and lowered S.N. content. Activation of Lp-system or
H202-treatment reduced the S.N. content especially in the latter.
The same trends was observed with tyrosine and tryptophan
content, shilovitch No. and TVFA content.
7-There was no apparent differences in the electrophoretic
patterns of cheese protein due to the Lp-system or H202-
reatments.
a-The microbiological analysis of the cheese (T.C, coliforms,
lipolytic and proteolytic bacterial count) showed that Lp-system
and H202-treatments have an inhibitory effect on all the flora
existed, and that H202-treatment has a stronger antimicrobial
effect than Lp-system.
9-Using Lp-system treatment produce cheese with satisfactory
quality and ranked high scores within the visinity of that made
by the traditional method (10% salt). H202-treatment aquired
lower scores.
Section B: Yoghurt
1-Lp-system and H202-treatments delayed the sitting time in cows’
and buffaloes’ milk.
2-The curd tension and curd synersis from Lp-system treatment was
almost the same as control in both cows’ and buffaloes’ while the
H202-treatment caused a softening in the curd with high amount of
whey exuded.
3-There was a slight decrease in the pH and increase in the
acidity of the yoghurt made from preserved milk than the control
in both cows’ and buffaloes’.
4-No probable differences could be seen in T.S.,Fat and T.N. of
yoghurt due to preservatives. But, they were higher in buffaloes’
yoghurt than that of cows’.
5-A slight variations were observed in N.P.N. ,T.V.F.A. and
acetaldehyde contents due to Lp-system and H202-treatment of
yoghurt milk and also due to kind of milk.
6-The electrophoretic patterns of yoghurt protein made from
untreated,Lp-system and H,02-treated milk were almost similar in
both cows’ and buffaloes’.
7-The lactic acid bacteria, coliform and yeast & moulds counts
were the highest in untreated yoghurt and they decreased in Lpsystem
and H,O,-treated yoghurt and the reduction was more
drastic in the latter.
B-The Lp-system treatment has no effect on the quality of yoghurt
as the sensory scores were almost the same as control. While the
HzOz-treatment affected the quality of yoghurt and it ranked the
lowest score points. Yoghurt prepared from buffaloes’ milk of
different treatments scored higher points than that from cows’
milk. Storage improved the quality of yoghurt till 5 days after
which the quality decreased.
9-The effect of storage for 5 and 10 days was discussed for
all parameters.
Conclusion
-The keeping quality of raw milk can be prolonged to 10 h by
activation the lactoperoxidase system using 14:30 ppm of SeN
:HzOz. While the storage period can be prolonged to over 16 h by
adding second dose of 30 ppm HzOz after 4 h from the first dose.
-The previous preserved milk (16 h) by Lp-system treated milk can
be manufactured to low salt Domiati cheese (5% salt) with a good
quality.
-The Hzoz-treated milk with a concentration of 200 and 250 ppm
(for cows and buffaloes) can be manufactured after preservation
(16 h) to yoghurt and the treated milk can be manufactured to low
salt Domiati cheese (5% salt) with an acceptable quality.