The objective of the present work was to evaluate the effect of different commercial starter cultures on the rheological properties of yogurt during gelation. Yogurt samples were prepared using pasteurized and homogenized bovine milk (fat content 3.5%). Ten different commercially available starter cultures were used. Two of the starter cultures were probiotic. The process of structure formation during yogurt making was monitored using a custom made dynamic U-tube rheometer of novel design. The storage (G’) and the loss (G") moduli, strain, tanδ, incubation temperature and pH was recorded as a function of time. The starter culture type significantly affected the structure development and the acidification process of yogurt. The times elapsed before the commencing of the storage modulus rise, for the pH value of the samples to reach 4.6 and for the attainment of the maximum tanδ value, were influenced by the type of starter culture. The pH value at the starting point of gelation, the pH value at maximum tanδ, as well as the storage modulus value at pH 4.6, were affected by the starter culture type as well. Principal component analysis revealed that the starter cultures could be classified into 4 distinct groups and that every group was characterized by different rheological properties.
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