Whey Protein Denaturation of Uht Processed Milk and Its Effect on Rheology of Yogurt

Abstract

The denaturation of whey proteins in whole milk during processing by the indirect UHT and vat systems was determined. Whey protein denaturation plateaued at about 88% following a UHT heat treatment of 149°C for 10 s. However, it reached about 88% with a vat heat treatment of 82°C for 5 min and reached 95 to nearly 100% after 10 to 15 min. Vat processing under pasteurizing conditions at 63°C for 30 min resulted in less than 10% denaturation. The yogurts prepared from the vat processed milk had considerably higher structural firmness than those prepared from the UHT milk, as confirmed by the lower value of curd firmness and the higher shear stress of these yogurts. It was also found that the structural or curd firmness of yogurts prepared from UHT milk was highest when the milk was processed for 3.3 s process holding time and was lower when the milk was processed for longer or shorter process holding times. The results suggest that the vat process at 63°C or 82°C brings about a specific change in the whey protein which leads to formation of a firm structure. This change apparently does not occur during the brief UHT treatment.

Influence of calcium fortification on sensory, physical and rheological characteristics of fruit yogurt

“…They reported 56-64% reduction in initial apparent viscosity after 100 s at contant shear rate of 112 s À1 . The thixotropic nature of plain yogurt was observed by several other authors (Basak & Ramaswamy, 1994;Labropoulos, Palmer, & Lopez, 1981;Mottar, Bassier, Joniau, & Baert, 1989;Ramaswamy & Basak, 1991, 1992Steventon, Parkinson, Fryer, & Bottomley, 1990). Fig.…”

Proteomic profiling of the coagulation of milk proteins induced by glucono-delta-lactone

“…However, we found that, although the pI of b-LG is 5.2, only a portion of the b-LG was depleted by the additions of 0.4 and 0.5 M GDL, indicating that b-LG remains in solution at its pI. Labropoulos, Palmer, and Lopez (1981) reported that the pasteurization of milk at 63 C for 30 min resulted in less than 10% denaturation of whey proteins, including b-LG. This is a clear indication that heating milk proteins causes a portion of the b-LG to unfold, which cancels the hydrophilic, negatively charged nature of the surface.…”

Rheological characterisation of almost intact and stirred yogurt by imperfect squeezing flow viscometry

“…The rheological properties of yogurt have received considerable attention in the food literature. 1±3 They were primarily evaluated by testing the gel's strength (eg Modler et al, 4 and Mottar et al 5 ), coaxial viscometry (eg Labropoulos et al, 6,7 Parnell-Clunies et al, 8 Mottar et al, 5 Ramaswamy and Basak 9,10 and Skriver et al, 11 ) or dynamic testing (eg, Keogh and O'Kennedy 12 and Ozer et al 13 ). In both coaxial viscometry and dynamic testing the specimen is pressed into the narrow gap of the sensor and is subsequently subjected to a steady, increasing, decreasing or oscillatory shear.…”