These are strain sweep These are time sweep These are frequency sweep These are temperature ramp Laboratory Report Guidelines Components of the report Contents 1. Introduction (Title, objective/aims...

DYNAMIC OSCILLATION OF LOW AND FULL FAT YOGHURTS
INTRODUCTION
Yoghurt is made by mixing a milk with yoghurt starter which leads to the fermentation process. In the fermentation process, development of lactic acid and specific flavor components are responsible for the particular taste of yoghurt. Main starter bacteria in the fermentation process are Streptococcus thermophilus and Lactobacillus delbrueckii ssp. Bulgaricus. Milk protein structure transforms due to the development of lactic acid and the reduced pH.
Milk have two types of protein, which can be separated by lowering the pH. These are whey and casein proteins which constitute about 20% and 80% respectively. Whey protein remains in solution while casein precipitates at pH 4.7. Yoghurt is produced when this occurs.
The incubation period required for the stirred yoghurt to reduce lactose which forms when the yoghurt is held in large vats then subsequently filled into retail containers. The incubation for set yoghurt occurs after filling into containers.
Rheology of yoghurt is dependent on the chemical compositions of the raw materials and the method used of yoghurt making. The nature of yoghurt is extremely shear dependent. When a small stress is placed on the gel, it will deform elastically. When strain sweep is implemented on set yoghurt, the initial storage G’ and loss G” moduli are independent of strain (flat traces), but eventually the network breaks down and both moduli collapse. Thus at high levels of applied strain samples behave like viscoelastic liquids and the values of G” overtake those of G’.
As the linear viscoelastic region is formed, network strength of yoghurt can be recorded using frequency sweep. Typically, a frequency sweep monitors the development of G’, G” and tan delta (G”/G’) within the frequency range of 0.01 to 10 Hz.
OBJECTIVE
1. Operating a rheometer.
2. To study rheometer for fundamental and applied tests.
3. Study deformation rheological techniques to evaluate the structure of yoghurt.
4. Determine temperature, time and applied strain of to study properties of yoghurt.
MATERIAL
· Stirred yoghurt
· Pot set yoghurt
· ARG-2 rheometric instrument
PRINCIPLE
To study viscoelastic and rheological properties of food products,the ARG-2 rheometric instruments are used. It is necessary to study viscoelastic properties of a food system as it goes through structural change for example, gelation, and these processes directly showed into the textural properties of the material.
Small deformation computations are applied by Rheology instruments on food products thus preserving the network structure of materials. Hence, it’s important to study rheology which is used to study the food biomaterials also it’s essential in the areas of product development and quality control. In this practical, viscoelasticity properties are studied for pot set yoghurt and stirred yoghurt.
METHODS
· Yoghurt Analysis Using Rheometry
1. Strain Sweep Test
Take out the yoghurt from the refrigerator and load carefully a on the bottom plate of the rheometer. This should be preset at 5°C. Down the top plate which is 4 or 5 cm in diameter. Implement a strain sweep using a strain range and a frequency value of your choice.
2. Time Sweep Test
Load fresh sample from the beaker on the measuring geometry. Apply a frequency and strain within the linear...