Rheological and Sensory Properties of Yogurt from Skim Milk and Ultrafiltered Retentates

The rheological, sensory, and some chemical characteristics of yogurts made from skim milk (SM) and ultrafiltered (UF) SM retentates were compared Gel structure development due to lactic acid fermentation was a multistage process for both UF and SM products. Following the onset of gelation, a local maximum in phase shift angle, delta (tan delta = G ''/G'), was evident, suggesting a partial loosening of the coagulating casein network before the ultimate macrostructure was established. UF retentates gave coagula of higher viscosity and elastic modulus (G') compared to SM of equivalent solids level. UF yogurts had slightly higher amounts of acetaldehyde, pyruvic, acetic and lactic acids, and lower amounts of orotic and citric acids than SM yogurts. Scores for perceived thickness and graininess determined by sensory analysis were higher for the UF products; products made from UF retentates at 12% solids were rated highly for all sensory properties.