The application of quality control on a regular basis is regarded as necessary for all types of meat plants.
- Sensory evaluation
In the simplest way of sensory testing, the meat processor, possibly assisted by other staff, will test a product’s color, smell, taste and texture upon manufacture. A team of trained panelists can be used in order to make the results as objective as possible. For this purpose, it is useful to have an appropriate testing room available with lights, temperature and seating arrangements with individual testing compartments so as not to distract the members of the panel.
Common test methods used in sensory evaluation are:
- Paired comparison test for simple difference: where two coded samples are presented to the panelists for evaluation on simple difference (Fig. 418).
- Triangle test: where three coded samples are presented at the same time, two are identical and the third is odd and the panelist is asked to identify the odd sample (Fig. 419).
- Hedonic scale rating test or acceptability test: where samples are tested to determine their acceptability or preference (Fig. 420).
Fig. 418: Score sheet for Paired-Comparison Test for Simple Difference
Physical Test Methods
With physical test methods important parameters such as temperature, acidity (pH), water activity (aw) and water binding capacity can be determined. Other physical parameters are light intensity and mechanical testing for texture.
Temperature measurement with thermo-elements/thermocouples is based on the thermo-electrical effect. The following is the physical principle:
“On one welding point of the thermocouple the reference temperature is taken. The other welding point is the tip of the metallic thermo-sensor of the instrument, which is exposed to the temperature to be measured. Both welding points are of different temperature, which generates the electric current within the system. The electric tension (voltage) is equivalent to the temperature difference between the two points and can directly be translated into the temperature reading on the instrument.”
For the correct functioning of the system, the reference temperature must be at a constant level.
Fig: Electronic thermometer (digital)
Portable instruments are battery driven and have glass electrodes. The pH–value in meat and meat products can be measured by direct contact between the sensitive diaphragm of the electrode and the meat tissue.
- Through the diaphragm differences in electrical load between the meat and electrolyte solution (e.g. Potassium chloride KCl) inside the glass electrode are measured and directly indicated as the pH-reading.
- In raw fresh meat, it is recommended to spray small amounts of distilled water onto the tissue at the point of measurement (prior to inserting the electrode), because the operation requires some fluidity in the sample and the glass electrode should be thoroughly wet.
|Fig: Portable pH-meter for direct measurement in meat||
Fig: pH meter
pH measurement is useful for:
- Evaluation of meat quality for further processing, in particular the water binding capacity
- Control of ripening of raw fermented products, which is connected with drop in pH
- Control of acidity of ingredients such as brines, marinades etc.
The ratio of the existing (absolute) vapor pressure of water in air to the saturation vapor pressure (= maximum amount of water vapor that can be held) in air of the same temperature
Hygrometers measure the relative humidity and are used in production and storage rooms of the meat industry.
AW – meter (mechanical instrument)
- The amount of free water in a product is equivalent to the air humidity produced by a product sample in a small enclosed system. This is the principle of the simple aw-measurement method. The product sample is placed inside a hermetically closed small can-like container.
- Pure water (representing 100% free water) is equivalent to aw-value of 1, all other food samples have lower aw-values than 1 depending on their free water content.
|Fig: Set of two simple aw meters enabling simultaneous measurements of two samples||
Fig: Aw-meter with product sample to be tested, lid (has to be attached) with built-in hygrometer
Water holding capacity
It is important in meat batters, which have to undergo heat treatment. Low WHC results in separation of jelly and/or fat during heat treatment. The WHC can be measured using a glass compressorium, where the sample of meat or batter is compressed onto a water absorbing sheet of paper. The larger the water infiltrated area on the paper, the poorer is the WHC of the meat/batter.
|Fig: Compressing meat sample|
Instruments for texture measurement
Sensory testing (chewing) is normally sufficient to test tenderness/toughness or homogenous/fibrous structure of meat and meat products. The instruments measure the shear-force necessary to cut through meat/meat products (Fig. 432, 433). Comparative texture measurements are usually taken from same tissues or products which were submitted to different treatments such as ripening, cooking etc.
(Protein, fat, water, ashes)
Moisture content: by oven drying method
Protein content: Kjeldahl method
Fat content: Soxhlet apparatus
Fig: Microwave oven
|Fig: Kjeldahl distilling apparatus
|Fig: Soxhlet extraction apparatus
|Fig: Muffle furnace
The defatted samples are then used for ash analysis by subjecting it to a temperature of +600°C in a muffle furnace for two hours. The weight of the ash is used to calculate the minerals content in % (weight of ash, divided by total sample weight, multiplied by 100).
Microbiological Sampling and Testing
Contaminating bacteria are removed from the surface to be tested by using a sterile swab. Standardization by using a reference square area is needed (e.g. by sterile metal frame). Microorganisms collected by the swab technique are rinsed off with sterile water. The microbial content of the liquid is tested.
- Advantage: Even in case of heavy contamination, the number of microorganisms can be determined by applying dilution techniques (see page 335).
- Disadvantage: Part of the contaminating flora may not be recovered, in particular in case of uneven rugged surfaces, e.g. meat.
Fig: Swab method
a) Total Plate Count (using nutrient agar)
For determination of the number of viable or living microorganisms in a sample.
b) Selective Plate Count
The total plate count is a good indicator for the overall bacterial load of meat and meat products. But, it does not tell about harmfulness of microbes.
Therefore, practicable microbiological standards should, in addition to the total plate count, always include the number of hygienically sensitive microorganisms, which can be used as an indicator for specific hygienic risks.
Enterobacteriaceae: The selective culture medium used for the determination of Enterobacteriaceae is the Violet Red Bile Agar (VRB), which contains Crystal violet and bile salt for the inhibition of all other bacteria
Other commonly used selective culture media are Lactobacilli MRS Agar for the isolation of Lactobacillus, BAIRD-PARKER Agar for the isolation of Staphylococcus aureus, XLT4 for the isolation of Salmonella and Mc Conkey Agar for the isolation of moulds.
|Fig: Selective medium for Lactobacillus
(small white colonies)
|Fig: Selective medium for Staphylococcus aureus
| Fig: Selective medium for Salmonella species