Determine Viscoelasticity and Spreadability of Cream Cheese

Cream cheeses are viscoelastic soft solids. Other than taste, their physical properties such as hardness, viscoelasticity and spreadability are also critical to satisfying consumer’s needs. Rheology is a useful technique that can provide quantitative evaluation of the viscoelastic properties of cream cheese samples. The rheological properties of three different types of cream cheese: Original, Low-fat, and Spread, were measured using a TA Instruments Discovery HR-30 rheometer. The oscillatory frequency sweep test was used to compare the differences in hardness and elasticity. The yield stress of cheese was measured using an oscillatory amplitude sweep. The flowability and spreadability of cheese were estimated using both shear flow and squeeze flow test methods. INTRODUCTION Cream cheese is a popular food ingredient. Its rheological and textural properties are both important to the consumers’ sensory experience. Cheeses are manufactured from various combinations of milk and cream. The differences in cheese ingredients and processing conditions have big impacts on their final physical properties such as hardness/firmness, elasticity, and spreadability. [1-4] Many analytical tools such as texture analyzers, hardness testers, and rheometers have been used in characterizing the physical and mechanical properties of cream cheese. Among them, rheological methods are the most frequently used. Rheological testing provides quantitative evaluation of the viscoelastic properties of cream cheese. Rheology can measure the modulus, which correlates to the mechanical strength, elasticity, and yield stress. Rheological measurements can also estimate the flowability and spreadability of cream chesses with different formulations. In this applications note, 3 different type of cream cheeses were measured using a TA Instruments Discovery Hybrid Rheometer. EXPERIEMNTAL Three commercial cream cheeses, which are identified as Original, Low-fat, and Spread were used in this study. All measurements were conducted using a TA Instruments Discovery HR-30 rheometer with Peltier temperature control system. The test temperature was set isothermally at 10 °C. In order to avoid wall slip during the measurement, a 25 mm and a 40 mm crosshatched parallel plates were used (picture shown in figure 1). A dynamic frequency sweep test was programmed with a frequency range from 0.1 to 100 rad/s using a strain that is within the linear viscoelastic region (LVR) of the sample. Yield stress was measured using a dynamic amplitude sweep procedure at a frequency of 10 rad/s. The yield stress was measured by taking the onset value of the storage modulus versus stress curve. Cream cheese spreadability was measured using 2 different methods: First, a shear flow test was setup from a shear rate of 0.001 1/s to 10 1/s. During the measurements, edge fracture and slippage were observed at shear rate greater than 1 1/s. Second, a squeeze flow test was performed at a constant linear axial rate of 0.1 mm/s. Sample was loaded to a 25 mm crosshatched parallel plate with an initial gap at about 3 mm. An axial squeeze test was conducted from 3 mm gap down to 1 mm at an axial rate of 0.1mm/s. During the test, shear velocity was locked at 0 rad/s. The axial stress was monitored as a function of time and gap change. Figure 1. Picture of TA Discovery HR-30 rheometer with a crosshatched parallel plate geometry