Evaluation of Microbiological and Chemical Quality of Yoghurt Produced in Two Factories in Khartoum State

Abstract

The present study was undertaken with the aim of studing the quality of standard yoghurt and planned to evaluate titrable acidity and pH.by comparing The quality of two different local market yoghurt, in Khartoum state, was compared examining microbiological and chemical changes of the product over a period of time of fifteen days, identifying the contamination by yeasts and moulds, Coliforms, E.coli, Klebseilla and Staphylococcus aureus taking into concern any other pathogens that might appear and attempting characterize some of the physiological factors for their growth in market yoghurt. Eighty five samples of yoghurt were collected randomly from two yoghurt factories (A and B) at zero time of production and analyses were done. The samples were stored at 4ºC refrigerator and a specific number of samples were examined everyday following Staggered Design II for the evaluation of the shelflife of yoghurt. All samples were inoculated on different bacteriological media and a number of biological tests were performed for the confirmation of the isolates. The titrable acidity and pH were determined to help to evaluate the quality. The average growth counts(cfu/g) results of 15 days were specified as follows; of factory (A) the average count of E.coli was nil and of (B) were (3.5x10³)),(0.20x10³)), (2.7x10³)),(1.92x10³),(3.77x10³),(4.03x10³),(6.21x10³),(3.52x10³),(2.94x10³),(0.43x10³), (0.82x10³),(0.11x10³) and (0.7x10³) and for Klebseilla no growth of factory (A) versus 17 20% growth on the samples of factory (B). The average growth of S.aureus of (A) was nil where the average count of (B) in 15 days were as follows: (2.9x10³), (0), (3.3x10³), (0), (4.5x10³), (4.8x10³), (0), (0.61x10³), (1.2x10³), (0),(0), (2.3x10³), (0.11x10³), (0) and (1.66x10³). The average yeast count of (A) in 15 days were as follows: (5.2x10), (0), (3.8 x10), (0), (4.9 x10), (5.8 x10), (5.2 x10), (7.3 x10), (3.3 x10), (4.3 x10), (4.2 x10), (4.8 x10), (6.2 x10), (7.5 x10) and (7.3 x10) and of (B) was (8.8 x10), (0), (6.7 x10), (0), (5.2 x10), (7.9 x10), (10.7 x10), (12.6 x10), (20.5 x10), (23.1 x10), (13.7 x10), (43.9 x10), (10.4= x10), (Uncountable)( Uncountable). Also the average mould count of (A) in 15 days was found as (1.3 x10), (0), (0.2 x10), (0), (0.9 x10), (0.5 x10), (1.2v), (1.1 x10), (2.8 x10), (5.5 x10), (4.2 x10), (6.9 x10), (4.7 x10), (3.5 x10), (5.3 x10), and of (B) was (4.x10),(0),(2.3 x10),(0),(1.5 x10), (3.2 x10), (3.4 x10), (2.8 x10), (6.6 x10), (8.6 x10), (10.0 x10), (9.4 x10), (12.2 x10), (14.6 x10), (10.0 x10). The results of the chemical tests were as follows; the average pH value of factory (A) was (4.29), (0), (4.35), (0), (4.32), (4.33), (4.38), (4.30), (4.33), (4.35), (4.28), (4.29), (4.30), (4.42), (4.32) and of (B) was (4.34), (0), (4.33), (0), (4.25), (4.35), (4.33), (4.32), (3.66), (4.29), (3.72), (4.77), (4.05), (4.68), (4.03). The average titrable acidity of factory (A) was (0.14), (0), (0.13), (0), (0.14), (0.15), (0.13), (0.14), (0.13), (0.15), (0.13), (0.14), (0.14), (0.15), (0.13), and of (B) was (0.89), (0), (0.87), (0), (1.13), (1.29), (0.95), (0.78), (0.84), (1.32), (0.82), (0.89), (0.32), (0.86), (0.82). The chemical analysis revealed that samples of factory (A) were consistent and hardly showed any variation in pH and acidity as compared to samples of factory (B). Microbiological examination of factory (A) showed nil growth of Coliforms or S.aureus and the typical growth of yeasts and moulds was within the permitted level throughout the fifteen days unlike factory (B) which showed a significant growth of E.coli, and S.aureus but the average growth of yeasts and moulds was scarcely higher compared to factory (A) on the first eight days and increased far more above the acceptable level on the next seven days of the examination. On refering to the titrable acidity and pH readings of factory (B) it was obvious that, unhygienic actions were practiced ending with poor quality yoghurt, unlike the results of factory (A) which were indicative to good practice of control.