摘要：The milk used for the manufacturing of set yoghurt in Khartoum State, Sudan includes recombined whole milk powder or a mixture of recombined whole and skim milk powder. This study was carried out to evaluate the microbiological quality of set yoghurt made from whole or mixed recombined milk powder during the storage period. Ten yoghurt batches (5 from each) from a modern dairy factory were examined a well milk samples from which the set yoghurt were to be made. The set yoghurt samples were collected immediately after processing. The samples were stored to determine their shelf life. High total bacterial count were reported both in mixed (52.55×105) and whole milk powder (12.16×105) used for production of set yoghurt, which indicated poor quality of milk. Moreover even after pasteurization of milk, high numbers of bacteria was found to survive, this could be due to improper pasteurization or poor handling of raw milk materials. The microbial content revealed significantly (P<0.05) lower levels of total bacterial count (TBC) in mixed set yoghurt (6.06×1011± 1.86 ×1012 cfu/ml) compared to whole set yoghurt samples (1.23×1012± 2.85 ×1012 cfu/ml). Moreover coliform bacterial count was recorded to be highly significant(P<0.05) in whole set yoghurt (10.80×104± 28.00 ×104 cfu/ml) compared to mixed set yoghurt (74.12×103± 30.31 ×104 cfu/ml). However the Streptococcus spp. count was found to be high in mixed set yoghurt (2.74×109± 15.13×109 cfu/ml) compared to whole set yoghurt (1.50×109±52.87×108 cfu/ml). Similarly Lactobacillus spp. count was recorded to be high in mixed set yoghurt (3.35×109±16.15×109 cfu/ml) compared to whole set yoghurt (1.08×109±31.55×108 cfu/ml). Moreover Streptococcus spp., showed more growth compared with Lactobacillus spp during the storage period. The results of this study concluded that quality of set yoghurt produced by this dairy factory need to be improved, as was indicated by the high count of TBC and coliform bacteria, which exist in the product up to 7 days of storage. Hence the present study recommends the application of hygienic control using HACCP systems in the dairy plants and training of the labours on the best manufacturing procedures.
