CHEMICAL, PHYSICAL, MICROBIOLOGICAL AND SENSORY CHARACTERISTICS OF SOME PLAIN AND FLAVORED YOGHURT IN EGYPT

Fifty one samples of plain and flavored yoghurts were collected from four native firms (A, B, C and D). All samples were kept at 4^oC/14 days. Samples were chemically, rheologically, microbiologically and organoleptically analyzed when fresh and periodically after 7 and 14 days of storage. Main chemical components such as T.S, fat and total sugars were determined in fresh samples. The obtained results revealed that total solids and total sugars were higher in flavored yoghurts than that of plain yoghurts while fat content of flavored yoghurt was lower. In general, it was found that the pH of collected flavored yoghurt samples was higher than that of its correspondence plain yoghurt. Upon storage the pH in both collected yoghurts was decreased. Regarding the acetaldehyde content, the obtained results generally indicated that collected flavored yoghurt samples contained higher acetaldehyde as compared with their plain correspondents. Upon storage, the acetaldehyde content of some plain and flavored yoghurt samples was increased and decreased in some other yoghurt samples. Viscosity of collected flavored yoghurt when fresh and during storage was lower than that of plain one. Microbiological analysis exhibited that the total bacterial count (TBC) was affected by the type of flavoring material added. In general, the use of blackberry led to increase the TBC of the resultant product. The TBC of collected samples was decreased upon storage. Referring to the starter culture (Streptococci and Lactobacilli) it was seen that the count of Streptococci was significantly higher than that of Lactobacilli. Both the two organisms were decreased upon storage. No coliform and Salmonellae bacteria were detected in all yoghurts while, few colonies of moulds and yeasts were detected during the storage period. The percentage of positive samples was 47% out of 51 samples. Sporeformers were detected in all collected fresh samples and significantly decreased during storage. Whereas, psychrotrophics were detected in 58.82% out of 51 samples and insignificantly increased during storage. The present work delineated that marketed plain and flavored yoghurts produced by large scale firms were highly acceptable and no changes in organoleptic properties were noticed during its shelf-life.