Bioyogurt was manufactured using the new probiotic LAB strains isolated from infant feces {Ent. faecium NM113 (T1), Ent. faecium NM213 (T2) and Lb. casei NM512 (T3)} in addition to the standard yogurt culture (1:1). The resultant yogurts were stored at ~ 5°C and analyzed when fresh and after 7, 14 and 21 days. The obtained results can be summarized as follows:
Addition of probiotic strains to the yogurt starter cultures increased the coagulation time of bioyogurt with different rates compared to the control yogurt. No significant differences were observed for chemical composition (TS, fat, protein and ash content) between the treatments of yogurt. The acidity percentage of all treatments increased during storage with different rates according to the starter culture used, while the pH decreased. Acetaldehyde content of all treatments significantly increased during the first 7 days of cold storage and then gradually decreased until the end of storage period. Also, there was a significant differences between treatments. The bioyogurts had higher acetaldehyde content than control.
Rheological parameters including firmness and whey synersis of yogurt treatments were affected by the type of starter used and storage period. Viable cell counts of LAB icreased during cold storage through the first 7 days then they decreased thereafter gradually till the end of storage period. Concerning the viable cell counts of the new probiotic isolates, Lb. casei NM512 showed the same trend, but the Enterococci gradually decreased during storage till the end of the period. The viable cells of the probiotics at the end of storage period remained >107 cfu g-1. Coliforms and yeasts & moulds of the resultant yogurts were not detected either when fresh or after 21 days of cold storage. All the resultant yogurts were accepted and free from defects and gained high scores when fresh and allover the storage period. The bioyogurt was comparable, but almost higher, in appearance, flavor, texture and overall quality to the standard yogurt. The best treatments were T2 and T3.
|
