Application note
RHEOLASER Master
Application Food |
Introduction Dairy products is a growing food segment especially for children and health conscious consumers. It is therefore critical to ensure the quality of the textural properties for consumer acceptance. Yoghurt and cheese is the result of a change in milk pH, which induces flocculation of the protein micelles. The flocculated micelles form the gel network. The pH reduction can be induced by addition of bacterial cultures, glucono-δ-lactone (GDL) or lemon juice to milk. Rheological measurements of dairy products are complex as the gel network is weak and can easily be disturbed by traditional methods like mechanical rheology. Rheolaser Master performs zero shear measurements , since no external stress is applied by the instrument. In this work we follow the yoghurt formation with GDL as a function of time and pH . Elastic properties of joghurts with different protein and milk fat content will also be compared. |
Objective Analyse the yoghurt formation as a function of time and pH as well as elastic properties of yogurts made from diffrent sources Device Rheolaser Master
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Gelling time of yoghurt Rheolaser Master measures the particle Mean Square Displacement ( MSD) , which gives an indication of the viscoelastic properties during gelation. Figure 1 .1 shows the MSD curves of milk gelated with 1 wt% GDL at 40°C. This yogurt sample with UHT milk and 1 % GDL gelled at 42 ‘25”. The pH was measured in parallel and the gelation took place at a pH of 5.11, as expected. Fig 1: 1 MSD curve evolution as a function of time during yogurt formation. Fig 1.2 Scaling factors a and b as a function of time. Influence of protein content Fig 2 below shows the evolution of the EI during gelation for different GDL/ protein ratios. With an increasing GDL/Protein ratio , more proteins are acidified and able to form the a network. As a consequence ,the EI increases and gelation took place at shorter times. (Gel points were opbtained with the TCS method). |
Rheolaser Master offers: |
Influence of variation in milk quality One challenge in processing milk into yoghurt and cheese is the variance in the natural character of milk supplied due to changes in feed quality and normal seasonal changes.
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