الفهرس 
NTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Ras cheese produced by ultrafiltartion has many advantages on
the economical, technological and nutritional levels. On the other hand,
it counteracted by slower ripening, hard texture and lack of flavour
than traditional one. Due to growing interest in the application of
ultrafiltartion in hard cheese making and the current interest for
producing the cheese flavour compounds, it would be important to
improve the quality parameters of Ras cheese from UF- retentate and
to produce Ras cheese flavour compounds (RCFC). This study was
planned to accelerate and enhance the flavour and texture development
of Ras cheese and attempting to produce the accelerated flavour of Ras
cheese for industrial applications. So, Lipase enzyme (from Rhizopus
oligosporus with specific activity 50.000 U/g), Transglutaminase
enzyme with specific activity 20 U/g (TG) and mature Ras cheese
slurry system were used to evaluate their effects on the acceleration of
ripening and the development of texture and flavour of Ras cheese
during ripening period at 12±2ᵒ C for 90 days. The study revealed that
the addition of microbial lipase to Ras cheese milk, at 50.000 U/15 kg
UF retentate, could be recommended for accelerating the development
of flavor and texture qualities in Ras cheese produced from UFretentate.
On the other side, enzymatic crosslinking of milk protein by
TG enzyme increased the moisture-to-protein ratio of the experimental
Ras cheese leading to increased textural hardness, gumminess and
chewiness values. Mature Ras cheese slurry that used in the
manufacture of Ras cheese from UF-retentate could be considered as a
valuable way for accelerating the ripening of Ras cheese and
enhancing the microstructure and flavour score of resultant cheese. In
addition, Ras cheese flavour compounds (RCFC) was prepared by
using lipolyzed cream and Ras cheese curd prepared from skim milk.
Microbial lipase (with activity of 40.000 U/g) from Rhizomucor mehei
was used at 12000 U/kg fat in the preparation of lipolyzed cream (35
70
% fat). Based on the chromatographic separation and identification
using GC-MS spectrometry in addition to the sensory evaluation of the
prepared RCFC samples, various classes of volatile constituents have
been identified as being responsible for the final aroma and taste of
RCFC samples. The addition of 30 % lipolyzed cream into skim milk
curd and stored for 7 days at 37ᵒC enhanced both chemical
composition, organoleptic evaluation and the flavour profile of
prepared RCFC samples and it can be a useful way for producing
RCFC. Moreover, RCFC was applied successfully in the acceleration
and improving the quality characteristics of Ras cheese prepared from
UF-retentate during the ripening period.
Key words: Ultrafiltration, Ras cheese ripening, cheese slurry, microbial
enzymes, microstructure, cross-linkage, Ras cheese flavour compounds (RCFC),
lipolyzed cream, volatile compounds.