Lesson 07 : Determination of quality of foods- objective methods
Types of viscometers
Stormer viscometer :It is used to measure the viscosity or consistency of certain food products and to give an index of the resistance of the sample to flow. The number of seconds required for the rotor to make 100 revolutions has been used to measure the consistency of some food samples.
Brookfield Synchrolectric Viscometer:This is based on measurement of resistance to rotation of a spindle immersed in the test material. This can be used successfully in measuring the consistency of custards, pie fillings, tomato products, cream style com, mayonnaise, salad dressings and dairy products.
Efflux-Tube Viscometer :It measures the time necessary for a quantity of fluid to pass through an orifice or capillary under standard pressure e.g. tomato puree.
Bostwick Consistometer This is used for measuring the consistency of tomato ketchup and sauce. The Bostwick consistometer consists of a channel (2x12") with sides which are 2” high. It has triggered gate on one side. A centimeter scale is etched on the floor of the channel. The use of this instrument is based on the theory that the length of flow is proportional to consistency.
Adams Consistometer While this consistometer was designed primarily for measuring consistency of cream style com, there are possibilities of using it in measuring the consistency of other products like tomato puree, apple sauce and fruit pulps. The Adams consistometer has been designed and constructed to accommodate a greater mass and measure the unrestrained flow in all directions by means of concentric circles. It consists of a large metal disc upon which are engraved 20 concentric circles, increasing 0.25 inch in radius. A steel truncated cone, which can be lifted vertically, fits tightly against the disc so that the circumference of the cone coincides with the inner most circle. Fill the cone with the sample to the level. Then raise the cone quickly and after 30 seconds, measure the consistency of the cream style com by recording the extent of flow of the product at four equidistant points as indicated on the calibrated disc. Average the four values thus determined to obtain an average consistency value for the product. A simpler version of this principle is used in Line spread test.
Penetrometer A penetrometer also may be used to measure tenderness of some foods. This device consists of a plunger equipped with a needle or cone that is allowed to penetrate the sample by gravitational force for a selected period of time. The larger the reading the longer the distance the more tender is the product. Gels and many baked products are particularly well suited to tenderness measurements using the penetrometer.
Bloom gelometer : It is a special type of penetrometer in which lead shot drops into a cup which forces a plunder into the sample. When sufficient weight has been added to the cup to move the plunger a set distance, the test is completed and the amount of shot required is determined as the measure of the test.
Brabender Farinograph This is used to measure the plasticity of wheat dough for preparing bread products. It is designed to study the physical properties of the dough by recording the force required to turn the mixer plates through the dough. The force required increases as the solution develops during mixing and later decreases as solution is slowly broken down by over mixing. Instruments used for solids
Magness-Taylor Pressure tester (compression) It consists of a plunger of variable diameter which is pressed into the fruit to a given depth. The sprint attached to the plunger contracts and measures the compression force e.g. peas (suitability of peas for the harvest or to find out the correct stage of ripening of a food).
Succulometer (compression) This instrument is used to measure the maturity of corn and storage quality of apples as determined by the volume of juice extracted under controlled conditions of pressure and time.
Tenderometer (compression and shearing) Compression and shear is applied to measure the tenderness of peas. It utilizes a multiple needle probe that is pressed into food eg. the rib eye muscle of raw beef .The force needed is sensed by a transducer and displayed on a meter. The carefully engineered needle probe was designed to give readings that correlate with the tenderness of the meat after cooking, while at the same time not altering the raw meat for further use. This is an example of an instrument based on shearing force in which compression is preceded by shearing action e.g. suitability of peas for preservation.
Voldokevich bite tenderometer (cutting and shearing) This attempts to imitate the action of teeth on food. It records the force of. biting on a piece of food which results in deformation and this determines the total energy utilised for this deformation e.g. meat and meat products.
Fibrometer This is based on the cutting principle and used to differentiate mature stocks from the tender stocks e.g. green beans.
Shortometer This device consists of a platform containing two parallel, dull blades on which the sample rests. A third blade is actuated by a motor to press down on the sample until the sample snaps. The force required to break the sample is the measure of the tenderness of the product.
Figure shows the instrument that measures the force required for a food to break with a bar attached to a motor. This finds out the breaking strength of idli, pastries and cookies.
Christal texturometer (cutting) This is designed with series of rods which are pushed into the meat sample. The harder the meat more force is required to penetrate.
Grinding and extensibility The power used by a household food grinder is measured. Increased toughness would increase the current power consumption of the grinder. Extensibility has proved to be inversely related to tenderness.
Kramer shear press This is a multipurpose instrument with same power unit and with different test cell assemblies. This instrument is widely used.
Succulometer Succulence or juiciness is associated with the moisture content, Kramer and Smith developed succulometer to measure the maturity of sweet corn. In this it uses the principle of compression to squeeze juice out of food as a measure of succulence.
Universal testing machine This is fitted with the appropriate devices which can measure firmness and crispness and other textural parameters. This and similar instruments frequently are connected to a moving recording chart. The time-force curve traced on the chart gives a graphic representation of the rheological properties of the food item. When an apple half is tested, the tracing would show an initial high degree of force required to break the skin, and then a change in force as the compressing-shearing element enters and passes through the apple pulp.
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