Rheological characterisation of almost intact and stirred yogurt by imperfect squeezing flow viscometry
✍ Scribed by Suwonsichon, Thongchai; Peleg, Micha
- Book ID
- 101225472
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 197 KB
- Volume
- 79
- Category
- Article
- ISSN
- 0022-5142
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✦ Synopsis
Samples of plain yogurt of two national brands, almost intact and after stirring for 1 min by hand and with a domestic blender, were placed in a wide shallow Te¯on R container. They were subsequently compressed with a wide Te¯on R plate to induce imperfect lubricated `squeezing ¯ow'. The recorded force versus height relationships were plotted on logarithmic co-ordinates. The resulting curves all had a clear linear part indicating the region where squeezing ¯ow was dominant. Its slope was on the order of À1.2 to À1.3 in the almost intact specimens and À0.5 to À0.9 in the stirred samples. The test reproducibility, expressed in terms of the coef®cient of variation (100s/x) was on the order of about 15% more than suf®cient to detect textural differences between the two brands and to monitor textural changes caused by stirring. These were expressed in terms of the apparent compressive stress at two preselected heights (1 and 2 mm) and the residual stress after relaxation for two preselected times (60 and 120 s). The ¯owability of the stirred samples was also expressed in terms of apparent elongational viscosity versus biaxial elongational strain rate relationships. All these mechanical parameters had a modest dependence on the upper plate diameter but the latter had no effect on their sensitivity as measures of yogurt consistency.
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