Laboratory Report Guidelines Components of the report Contents 1. Introduction (Title, objective/aims and background information) It presents relevant background with explanation on the focus of the...

TPA OF LOW FAT SPREADS
INTRODUCTION
During the last 20 years or so, people have responded to the call to reduce intake of fat in diet due to health consideration. A rising demand for low fat products has challenged food scientists to find fat replacers that could imitate the properties of fat. Biopolymers such as gums, cellulose, gelatin, starch, and milk protein are some of the ingredients used to replace fat. These biopolymers act as stabilizers of the aqueous phase and imitate the organoleptic properties of fat. One of the many popular low fat products manufactured today are spreads. Two types of low fat spreads that could be manufactured are fat continuous and water continuous. Fat continuous spreads comprise of 40% fat phase while water continuous spreads comprise 012% by weight of the dispersed fat phase and 88-100% by weight of a continuous aqueous phase.
To monitor the textural properties of mixed biopolymers gels in an attempt to identify satisfactory substitutes of fat in water or fat continuous products compression analysis is used. The rheological technique of compression analysis can be used to analyze the stress/strain characteristics of all types of structured foods. The characteristic curve of stress vs. strain for low fat spreads is of plastic dispersion. When purely plastic spreads are subjected to compression analysis, they produce a smooth compression curve with a shoulder in the middle part and with no apparent yield point that would create a curve with a negative slope. The characteristic features of stress/strain profile of plastic dispersion and gels are as follows:
DEFINATIONS
· Maximum stress, is the point where the stress goes through a maximum value
· Maximum strain, is the strain at the maximum stress
· Inflection point stress, is the stress at the inflection point of the curve where the stress goes through a minimum value following a sharp decrease at a strain slightly larger than the maximum strain
· Plastic stress, is the stress at a horizontal or near-horizontal portion of the curve (plateau) at a strain slightly larger than the maximum strain
· Ratio of inflection point stress to the maximum stress
· Ratio of the plastic stress to the maximum stress
OBJECTIVE
1. To familiarize ourselves with the textural properties of low fat spreads and the ingredients used to replace fat.
2. To familiarize ourselves with the use of the technique of compression testing using TPA TA-XT2 as texture analyzer.
3. To discuss the rheological properties of low fat spreads through stress-deformation relationships obtained by TPA.
MATERIALS
· TPA TA-XT2
· 5 Kg standard weight for calibration
· Butter:80-82% milk fat
· Margarine/Low fat spread: 40-70% milk fat
· Knives
· Thermometers
· Scales
· Freeze
PRINCIPLES
Texture profile analysis is used to obtain force-deformation curves. A cylindrical or cubical sample with a flat surface is placed between two plates and one of the plates is then made to move at a preselected constant speed.
The force developed is recorded as a function of distance (deformation) or time. The resulting force-distance curve is then interpreted by assigning textural properties to one or more parameters from the curves.
Compression Vs Penetration
-Sample size is smaller than probe size -Sample size is larger than probe size
-Area of contact is surface area of the sample - Area of contact is surface area of the probe
In this experiment compression test is performed on butter and margarine using two different probes sizes and two different temperatures. Compare effect of material composition(butter and margarine), probe size(25mm and 50mm) and temperature.
METHODS
LARGE DEFORMATION COMPRESSION TESTING
1. Turn on the computer and the TPA.
2. Open the Texture Analyser Exceed program.
3. Connect the probe to the TPA; Decide upon the type of experiment to perform and the size
of the plate of the probe.
4. Calibrate the probe using the TPA software.
5. Open a new Graph Window.
6. Adjust the Test Setting; Decide upon the compression / penetration rate, the size and shape
of the sample to compress, and the...