الفهرس 
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Abstract
Background: Yeasts defined as unicellular fungi, under bad hygienic measures,
contamination of fish and fish products by yeasts is common due to their wide
distribution in the environment and they can cause changes in taste and odour in
fish products because of their metabolic activities like their lipolytic and
proteolytic activities, which can also lead to spoilage of fish and fish products.
Aim: This study was undertaken to determine the total yeast counts, lipolytic
and proteolytic yeast counts in fish and fish products which were collected from
different places at Sharkia governorate and to determine of the effect of Moringa
oleifera leaves extract on yeasts growth in fish.
Materials and Methods: A total of 70 random samples of fish and fish products
were collected from different places at Sharkia governorate. Using of tryptone
glucose yeast extract agar media to enumerate total yeast counts. Proteolytic
activity was determined by using caseinate agar and lipolytic activity was
determined by using plate count agar accompanied with tributyrin. The
identification of the isolated yeasts was performed by procedure which included
two phases involved in the master key of simplified identification method
(SIM).
Results: The mean values of total yeasts count of fresh Tilapia nilotica, frozen
Pagellus acarne, frozen Trachurus indicus, frozen Lutjanus and frozen Atherina
were 3.76±0.18, 4.19±0.19, 2.49±0.30, 4.67±0.25 and 5.62±0.16 log10cfu/g,
respectively and the mean values of total yeasts count of frozen Pangasius
fillets (Pangasius hypophthalmus), frozen Sepia and frozen Tilapia fillets were
5.32±0.27, 2.37±0.42 and 4.12±0.09 log10cfu/g, respectively. The mean values
of proteolytic yeast counts of fresh Tilapia nilotica, frozen Pagellus acarne,
frozen Trachurus indicus ,frozen Lutjanus and frozen Atherina were 3.73±0.31,
4.20±0.01, 2.51±0.34, 4.59±0.22 and 4.59±0.24 log10cfu/g ,respectively and the
mean values of proteolytic yeast counts of frozen Pangasius fillets (Pangasius
hypophthalmus), frozen Sepia and frozen Tilapia fillets were 2.80±0.40,
2.68±0.43 and 5.24±0.22 log10cfu/g, respectively. while the mean values of
lipolytic yeast counts of fresh Tilapia nilotica , frozen Pagellus acarne, frozen
Trachurus indicus ,frozen Lutjanus and frozen Atherina were 4.44±0.13 ,
4.20±0.01 , 2.96±0.21, 5.03±0.11 and 4.92±0.23 log10cfu/g ,respectively and the
mean values of lipolytic yeast counts of frozen Pangasius fillets (Pangasius
hypophthalmus), frozen Sepia and frozen Tilapia fillets were 3.62±0.14,
1.82±0.35 and 5.06±0.27 log10cfu/g, respectively.
The isolates were identified to 4 genera including Candida, Cryptococcus,
Trichosporon, Rhodotorula. The results determined that C.glabrata showed both
proteolytic and lipolytic activities while C.tropicalis and Rh.glutinis showed
lipolytic activity and Cryptococcus spp. and Trichosporon spp. showed
protoelytic activity.
The effect of Moringa oleifera leaves extract on yeasts growth in fish flesh
(fresh Tilapia nilotica) during storage at 4oC throughout the 7 days, the mean
counts of yeast in fish flesh dipped in 5% concentration of Moringa extract were
3.67±0.11, 3.56±0.12, 3.20±0.17 log10cfu/g, the mean counts of yeast in fish
flesh dipped in 10 % concentration of Moringa extract were 3.67±0.11,
3.46±0.12, 2.41±0.15 log10cfu/g and the log mean counts of yeast in fish flesh
dipped in 15 % concentration of Moringa extract were 3.67±0.11, 3.22±0.12 ,
1.49±0.23 log10cfu/g, compared to 3.67±0.11, 3.67±0.11,3.70±0.10 log10cfu/g
in controls throughout the 7 days storage period.
Conclusion: from the results of the present study it can be concluded that there
is high level of contamination by yeast in fish samples collected from different
places in Sharkia during preparation, handling, processing and storage. This
study indicated that yeasts contribute to spoilage of fish and fish products
because of their lipolytic and proteolytic activities and yeasts especially
C.glabrata , Trichosporon spp. and Rhodotorula spp. play an important role in
spoilage of fish and fish products. The results indicate also that Moringa oleifera
leaves extract significantly reduced total yeast count.