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

Abstract

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.

Physico-chemical and sensory characteristics of steviolbioside synthesized from stevioside and its application in fruit drinks and food

“…Compression measurements were performed with a Texture Analyser (Texture Pro CT3 V1.2, Brookfield, Middleboro, USA) equipped with a 5 kg load cell at a speed of 1 mm/s to a distance of 20 mm with a 4 g trigger load for 30 s. The viscosity was measured with a rotary viscometer (Brookfield Model DV-II ? Pro, USA) at 30 rpm and 0.5 rpm at temperature 23 ± 2°C for apple and mango juices respectively (Suwonsichon and Peleg 1999). The colour values of all samples were evaluated by a Hunter Lab Ultra Scan VIS model, colorimeter (USA).…”

Structure and texture development of food-emulsion products

“…Food materials are squeezed between the tongue and palate as they move together during mastication, and strong elongational flow is created. Some instrumental methods do include both types of flow, such as tribology (see earlier), squeezing flow rheology (Campanella and Peleg, 2002;Chatraei et al, 1981;Corradini and Peleg, 2005;Pelot et al, 2013), and "imperfect" squeezing flow rheology (Damrau and Peleg, 1997;Suwonsichon and Peleg, 1999;Terpstra et al, 2007). Some instrumental methods do include both types of flow, such as tribology (see earlier), squeezing flow rheology (Campanella and Peleg, 2002;Chatraei et al, 1981;Corradini and Peleg, 2005;Pelot et al, 2013), and "imperfect" squeezing flow rheology (Damrau and Peleg, 1997;Suwonsichon and Peleg, 1999;Terpstra et al, 2007).…”

Viscosidade extensional e em cisalhamento de suspensões acidificadas de amido de amaranto e caseinato de sódio

“…Esta técnica está baseada na compressão de um produto por duas placas que devem estar lubrificadas com o objetivo de diminuir ao máximo o cisalhamento no produto, que neste caso é a superfície do alimento PELEG, 1999a;PELEG, 1999b;PELEG, 2002;HOFFNER et al, 1997). Uma desvantagem importante da técnica é que o padrão de fluxo não está bem definido, apresentando uma organização imperfeita e colocando em dúvida a validez dos modelos teoricamente ajustados.…”