الفهرس 
Organoleptic properties
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Abstract
This study aimed to produce Ras cheese of good quality from cow’s milk enriched with
different levels of solids not fat (8.5as a control, 12.5, 14.5 and 16.5 ), and accelerated the
cheese ripening by using £-galactosidase (lactozym preparation , isolated from
C/uyYero•ys .16ctis ) as well as deaeased the production requirements and manufacturing
time . This work was carried out in two parts:
PART 1 :
Production of Ras cheese from high milk solids : SECTION A:
Preliminary experiments on the use of high milk solids in Ras cheese making.
This section was conducted to through some light on the effect of some technological factors
(e.g. ) . solids level on the acidity development in cheese milk , and amount of
rennet on the properties of the resulting enrichment curd as well as the washing water
percent on the quality of the resulting Ras cheese . The results obtained could be summarized in
the following :
1. Ina-easing solids level , the rate of acid production as well as the final acidity
attained decreased considerably with adding of 1 starter .
2. The rennet coagulation time decreased in enrichment milk than cow’s milk with the same
amount of rennet .
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3. The curd made from enrichment milk was firmer than that produced from cow’s milk with
the same amount of rennet (6.3 ml/250 ml milk).
4. Addition of 3.8-5.0 ml of rennet solution to 250 ml of high milk solids (instead of 6.3
ml/250 ml of control milk) resulted in the formation of curd with firmness similar to that of cow’s
milk curd.
5. Addition of 20-30S warm water from milk weight instead of
whey off at scalding process resulted in improving the quality
of Ras cheese produced from high milk solids .
SECTION B:
Fffect of milk enriched with different levels of solids not fat on the chemical and organoleptic
properties of Ras cheese during ripening . l. The yield percent was increased in Ras cheese
made from
enrichment milk than the control one . The recovery of milk fat slightly increased with
increasing solids not fat level up to
14.5S , while more increasing solids not fat decreased the recovery of fat in the resulting
cheese .
2. The moisture content was less in Ras cheese made from high milk solids than the control
one when fresh and throughout the ripening period .
3. The titratable acidity was higher in enrichment milk Ras cheese than the control
one when fresh and along the ripening period.
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4. Lactose content of enrichment mill: Ras cheese was higher compared with control one when
fresh and during the ripening period.
5. Fat content (on dry basis , FDM) of all cheeses was fluctuated
along the ripening period .
6. No marked changes could be observed with respect to the salt content in all cheeses .
7. Soluble nitrogen/ total nitrogen percent in Ras cheese made from mill: of 12.6’ SNF was the
highest compared with the other treatments or control cheese .
8. Soluble tyrosine and tryptophan contents were increased in
Ras cheese from mill: of 12.61SNF than the other treatments or control one when fresh and at the
end of ripening .
9. Total volatile fatty acids content of enrichment milk Ras
cheesest ererugher than the control one when fresh and during the ripening period
I 0. The organoleptic evaluation of Ras cheese made from milk of
12.6’ SNF revealed higher total scores along the ripening period compared with other cheese
treatments (14.5 or 16.5’ SNF) , while the control cheese was the highest .
fi.naUy, it could be recommended that Hood quality Ras cheese oould be obtained from cow’s milk
enriched with solids not fat up to
12.6’( 18.1’TS) and washing the cheese curd with 20’water at 40 OC (from the milk weight) at
scalding process . It seem to be economic
·--. ’
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to decrease the required quantity of rennet and the manufacturing time , as well as incrasing the
cheese yield .
PART II:
Effect of adding B-galactosidase on the properties of enriched mi.l.k Ras cheese during
ripening .
1. The yield percent was increased in Ras cheese made from enrichment milk treated with
D-galactosidase than untreated cheese . Washing cheese curd had no marked effect on the yield
percent of the resulting treated Ras cheese . No much differences in recovery of milk
fat at the same solids of cheeses could be observed .
2. The moisture content of Ras cheese made from enrichment milk treated with
B-galactosidase was higher than those of Ras cheeses made ·ithout enzyme when fresh and during
the ripening period. Wa5hing the cheese curd had a slight effect on increasing the moisture
content of the resulting cheese .
3. Titratable acidity was higher in enrichment milk Ras cheese
treated with n-galactosidase than both cheeses made from high milk solids ·ithout enzyme or the
control one (9l SNF) . Washing cheese curd with !Ol warm water decreased the titratable
acidity of the resulting Ras cheese compared with the unwashed cheese curd when fresh and
along the ripening period .
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.f. No marked effect could be observed with respect to the salt , fat contents in all cheeses
at the same level of solids .
5. SN/TN percent in cheeses made from .high m.i.lk solids treated
with B-gaJactosidase were .higher than cheeses made without enzyme or the control one (91 SNF) .
Washing cheese curd increased SN/TN percent in the resulting cheese than the unwashed one when
fresh and throughout the ripening period .
6. Soluble tyrosine and tryptophan contents were higher in enrichment m.i.lk Ras cheese
treated with B-galactosidase compared with untreated Ras cheese or the control one . Also ,
washing cheese curd slightly increased soluble tyrosine and tryptop.ban contents w.ben fresh and
along the ripening period .
7. Total volatile fatty acids content of lactose hydrolysed enrichment mi.lk Ras cheeses were
.higher than untreated cheeses or the control one (91 SNF) . Washing cheese curd reduced the
total volatile fatty acids of cheese when fresh and during the ripening period .
8. The organoleptic properties of Ras cheese made from high milk solids treated with
13-galactosidase had higher total score points than untreated cheese or the control one (91
SNF) . Washing cheese curd slightly improved the organoleptic properties particularly the body
and texture .
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’Jfae auainaC mnits dearly indicate that the use of
6-galactosidase aa:elerated cheese ripening and improved the quality of Ras cheese made
from high milk solids . Furthermore , use of lactose hydrolysed enrichment milk in Ras cheese
making reduced the ripening period to about 2-3 months instead of 4 months in control cheese
(9S SNF) . Washing cheese curd with lOs water
at 40 OC, also improved the quality of the resulting Ras cheese .