Six fungal genera including thirteen species
isolated from Ras cheese samples were tested for assimilation of lactose, skim
and fat milk hydrolysis. All fungal strains gave negative results in lactose
assimilation except A. nidulans which produced acid without gas after 24
hr and produced a soluble red pigment after 10 days of incubation. All tested
fungal strains showed positive results for protein hydrolysis on modified
Czapek agar (MCA) medium by skim milk addition. The presence of casein in the
cultural medium caused a strong growth comparing with the growth on control.
Changing of growth resulting from milk casein addition was in the highest
values in the cultures of Rhizopus stolonifer, A. flavus and A.
niger being 87.81, 58.32 and 41.58 mm, respectively and the lowest values
were A. nidulans and Geotrichum candidum being 7.09 and 13.71 mm.
All strains gave positive results for lipolysis except Aspergillus nidulans on plates containing modified Czapek agar (MCA) medium by milk fat addition.
The fungal growth diameter was varied from 9.17 to 30.67 mm in the case of A.
niger and A. alliaceus, respectively. The presence of milk fat in
the cultural medium caused a changing of growth in the case of A. glaucus; A. alliaceus and A. flavus being 28.11, 27.42 and 25.19 mm,
respectively and A. niger, Rhizopus stolonifer and A. flavipes achieved lowest values being 5.62, 10.80 and 11.82 mm, respectively. Moisture
percentage was gradually decreased during
storage period (3 months at 15.5？C) from 31.29% in the first month to 30.25% in
the third month. Fat percentage was 24.05% in fresh Ras cheese wheels, which increased
to 25.89% after salting period (45 day). During ripening period the values of
fat in Ras cheese wheels were 30.53%, 35.98% and 32.38% after the 1st,
2nd and 3rd month, respectively. The highest values of
total nitrogen, soluble nitrogen and non-protein nitrogen percentages of Ras
cheese wheels were 4.18%, 43.97% and 18.98%, respectively. These values tended
to increase with advanced storage.
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