TEXTURE Dr. Mohamad Yusof Maskat Fakulti Sains Teknologi Universiti Kebangsaan Malaysia Bangi, Selangor

Introduction is very important physical property of foods assessed by consumers visually (appearance) and also during eating eg. during biting, mouthfeel

Texture is affected by several factors : –Mechanics or rheology –Geometry –Chemistry –Thermal –Acoustic –psychology

can be measured through objective and sensorial methods Both methods have advantages and disadvantages Advantages of objective method: –Test only involves small deformations –Sensory : involves large deformations, a lot of samples.

–Chewing involves a combination of compressive and shear forces. Less specific. –Chewing also involves increase in heat, according to body temperature. –Chewing involves external factors apart from the food eg. saliva containing enzymes, moisture. –Sensory evaluation may involves a combination of several sensory data eg. visual and not only mechanical.

there are several objective methods to measure texture it depends on the type of food and the physical properties to be measured Objective tests usually is based on the interaction between food and force Thus, only measures the mechanical and physical aspects only

is an advantage of objective methods –Eg. as discussed previously also serves as a weakness for objective methods –Eg. not comprehensive – limited to certain aspects; the eating process may be different

Objective measurement involves normal or shear force Normal force is a force which is perpendicular (90 o ) to the surface being acted upon produces tension or compression normal stress is defined as total force for each unit of surface area (F/A) Similar to pressure (P=F/A)

Normal force

Shear force is defined as a force parallel to the surface being acted upon shear stress is defined as total shear force for each unit of surface area (F/A)

Shear Force

For most material, external forces causes various types of internal stress Eg. bending of a material : –resulted in a compression and tension effect –also involves shear force and shear stress

Membengkok bahan

sometimes, application of a normal force also can produce a limited shear stress. among the commonly used tests are puncture test, shear test, compression test and others

Figure 1(d)

Application of force Objective tests use several approaches for force application depends on the properties to be studied i. Constant rate of deformation or displacement –Constant probe speed –probe will interact with food at a constant rate

Constant rate of deformation or displacement

ii. Constant rate of force increment –force is applied to the sample at a constant rate of increase –difficult to achieve using UTM –usually needs a hydraulic apparatus –not commonly used for food analysis –because the force range involved is usually larger than which is commonly used for food analysis.

iii. Step deformation or loading – application of force all at once and immediate – difficult to achieve ideally – because of limitations in instruments –usually considered as practical step deformation

Step Deformation or Loading

iv. Sinusoidal deformation –Dynamic deformation –force is applied according to a sinusoidal pattern –at a small maximum amplitude –different force frequency can be used

Sinusoidal Deformation

Deformation measurement involved the application of force to the sample measures force that deforms the sample frequently mimics the eating action measurement is based on –1. Maximum or minimum force –2. Curve pattern of form

Puncture test to measure product’s firmness use a probe that pierce into the food includes a spring to measure force the probe is pressed onto the sample’s surface force is applied until the probe punctures the surface and pierce into the sample

Puncture Test

Puncture test

maximum force is measured when the probe pierced the surface due to the force has reached a point where the surface yields to the force, hence, termed yield point after the sample is punctured, change in force differs according to sample type

Force Profile of Puncture Test

Compression test for measuring hardness of samples usually, compression onto one surface only eg. top surface sample is placed in a container subsequently, compressed for a certain distance eg. 80% from initial height of sample maximum force is recorded

2 type of compression test commonly used –1. Linear compression : sample is subjected to stress in one direction only. The other surfaces is not affected. –2. Bulk compression : sample is subjected to stress on all surfaces. Example, through hydraulic pressure.

Linear and bulk compression

Probes for linear compression test

Compression-extrusion test Based on compression test but including elements of extrusion force is applied until the sample is forced through a series of apertures or holes Maximum force needed is recorded used for viscous materials eg. Gels, shortenings

Example of force profile for compression-extrusion test

Extrusion force is inversely related to the width of the probe or space between the probe and wall of the container width of the probe also influences the smoothness of the curve the smaller the probe, the smoother the curve

Effect of probe width on the force profile of a compression-extrusion test

3 point bending test to measure the bending/flexibility or breakability of a sample Eg. breakability of biscuits, flexibility of jellies maximum force for flexing or breaking is recorded

3 point bending test

Shear test Definition of shear : –true shear : relative motion of parallel planes (satah) due to a tangential force being applied to one of the planes –cutting shear : any cutting action that divides a material 2 commonly used shear test –Warner-Bratzler shear test –Kramer shear test

True and cutting shear

Warner-Bratzler shear test to measure toughness of a product probe head consist of a 'V‘ shaped plate also have 2 additional plates on each side of the 'V‘ shaped the 2 side plates will hold the sample until the sample is cut by the 'V‘ shaped plate the maximum force needed to cut the sample is recorded

Warner-Bratzler shear test

Kramer shear test Mimics the action of biting Involves a combination ot several plates as probe Interaction between probe and sample involves several force action: –1. Compression –2. Shearing –3. Extrusion

Kramer shear test

Tensile test involves the action of pulling and stretching food samples not widely used in measurements of food systems low correlation with sensory data because during eating, the actions involved is more on compressive and shearing force

Tensile test

tensile test is also difficult to apply to foods due to the sample needed to be clamped at the end part Samples are pulled until it breaks it is hoped that the sample breaks normal to the direction of the force but sometimes the sample breaks at the clamped ends due to being soft Eg. tensile force of chewing gum, mee

Torsion test torsion is produced when a pair of force rotates an object represented by torsion force or torque used to study certain physical attibutes of samples not related to eating action Eg. Farinograph, rotational viscometer

Torsion force

Texture profile analysis (TPA) measurement of texture attributes by mimicking the act of chewing the probe will interact with the food 2 times change of force and time will be recorded from the force-time curve, texture attributes of the sample can be determined/ calculated

TPA force profile Distance 1Distance 2

among the attributes that can be determined are: i. fracturability –force needed to produce the first significant fracture during the first bite ii. hardness –largest force produced during the first bite

iii. cohesiveness –ratio of area under the positive curve between the first and second bite (Area 2/Area 1) iv. adhesiveness –work needed to pull out the probe from the sample after the first bite (Area 3) v. springiness –ration of the biting distance of the second bite with the first bite (Distance 2/ Distance 1)

vi. gumminess – hardness x cohesiveness vii. chewiness –gumminess x springiness

Universal Testing Machine (UTM) Instrument commonly used to analyse texture Brands : Instron (USA), Shimadzu (Jepun), TA (UK) Measures the change of force Now connected to computer can be attached with various probes

Single column UTM

twin column UTM

Shimadzu AGS-J

Shimadzu AGS-J Software

Linear measuring instruments Measures linear distances distance of food movements or distance of probe movements relates the linear ditance with physical attributes sometimes, more practical

Bostwick consistometer used to determine the consistency of semi-liquid or viscous foods eg. sauces, ketchup, puree a trapdoor will hold the sample and prevent it from flowing the trapdoor is immediately opened Sample will flow along the container

the distance covered by the sample in 30 sec will indicate the consistency of the sample the more viscous the sample, the shorter the distance travelled in 30 sec. but also will be influenced by other factors Eg. density, surface tension, wettability

Bostwick consistometer

Ridgelimeter Measures rigidity of gels eg. pectin gel Samples are placed on the instrument the probe end with a micrometer attached is lowered until it touches the sample the distance recorded by the micrometer is recorded after 2 minutes, the measurement is repeated the difference in distance is shown as %

Ridgelimeter

Haughmeter used to measure the quality of eggs the egg is broken and placed on a piece of glass the Haughmeter is positioned on the egg white at 10 mm from the egg yellow Micrometer is rotated until its end touches the egg white the more the distance traveled by the probe, shows a lower quality

Haughmeter

USDA consistometer developed by United States Department of Agriculture (USDA) Samples are prepared according to a certain dimension eg. height inches and diameter - 3 inches Samples are placed on a sheet with several concentric circles drawn and divided into quarters after 1 minute, distance of flow is measured in all 4 quarters and averaged

USDA consistometer

Hilker-Guthrie Drop Measures the consistency of semi-solid samples eg cream, yoghurt an aluminum tube is dropped onto the sample a scale on the aluminum tube allows the determination of distance penetrated by the tube into the sample the more viscous the sample is, the lesser the penetration will be

Hilker-Guthrie drop

Volume measuring instruments the sample is placed in a measuring box an amount of seeds enough to fill the measuring box when it is empty will be used the seeds will be poured into the measuring box containing the sample until the box is full

the volume of the balance of the seeds not used to fill the box is measured eg. graduated cylinder volume of sample = volume of balance of seeds not used to fill the measuring box

Bread loaf measuring instrument