Texture, flavor and appearance are key factors which influence food sampling, buying and repurchase. While flavor and appearance are well established in the sphere of quality control, texture is a relative newcomer in the determination of product acceptability.
Orally, visually, manually – texture is assessed in many ways to determine a wide range of properties: hardness, cohesiveness, springiness, adhesiveness, fracturability and chewiness. Major food companies routinely apply texture analysis techniques both in new product development and as part of quality control in finished processed foods.
The instruments of texture analysis
While subjective testing still plays a role, objective analysis is key to maintaining consistency and textural quality in manufactured foods. Food processors now use a number of instruments to provide quick and repeatable information as a cost-effective method for determining the effects of raw material quality and ingredient/process variables on end-product acceptability.
As demands on food manufacturers have become more pressing, texture analysis equipment has become more sophisticated. Instruments have developed from single textural parameter testing, such as penetrometers, to multi-functional instruments, including fully computerized systems, which carry out a variety of measurements.
Unrivaled simplicity and functionality
Multi-functional equipment uses different probes and fixtures according to the individual test. These fixtures, each designed for a specific application, can be attached to the analyzer’s base and/or horizontal arm. Samples are placed on the base of the instrument or on the lower fixture, or held between upper and lower fixtures.
A range of probes is available, including needle, cylinder, spherical and conical probes, to puncture or penetrate samples. An ever-increasing selection of fixtures is also available for compression, extrusion, cutting, extending or bending food products.
In a simple test, the arm of the texture analyzer, which contains the loadcell, moves down to penetrate or compress the product and then returns to its initial position. During testing, data characterizing the product is collected as time, distance and force values, at a rate of up to 500 readings per second. These values are typically plotted on Force/Distance or a Force/Time graph and then analyzed. The test results can be viewed in a spreadsheet, chart or report format. Coefficients of variations (C.V) account for variations between individual samples. Low C.Vs demonstrate reliability and accuracy of results.
Texture analysis throughout the food industry
Because of its adaptability, texture analysis has become commonplace throughout the food industry. Texture analyzers can now be found in food laboratories at dairies, meat processing plants, bakeries and many more. From keeping cereals crispy to making butter easier to spread on toast, texture is vital for ensuring consumer appeal and product success. The following tests are typical applications of texture analysis to ensure that everyday products meet the expectations of consumers.
The most critical performance factors of fats and oils are related mostly to consistency, plasticity, firmness and spreadability. But measuring these accurately can be problematic as fats are sensitive to temperature changes and prone to worksoftening.
Traditionally, the hardness and softness of table spreads (which subsequently affect spreadability) have been assessed using cylinder and conical probes. However, improved methods are now available that assess spreadability. In this instance, the sample is pressed into a female 90 degree perspex cone to eliminate air pockets and the surface is smoothed with a knife. A precisely-matching male cone is lowered into the sample, forcing the butter or margarine to flow upwards and outwards (at 45 degrees). The ease with which the sample flows is an indication of its spreadability.
Because temperature has a significant impact on the rheological properties of refrigerated spreads, the testing conditions need to be closely controlled. Cabinets that maintain constant temperature are vital when testing products such as butter and cake frosting.
For the consumer, a cookie’s ideal texture is both crunchy and crumbly without being too hard or falling apart. One of the most common tests carried out on cookies is the “snap” test, which aims to provide manufacturers with an objective assessment of how hard the product is. Users employ a ‘three-point bend rig’ which provides a base of variable support length up to 70mm and accommodates samples up to 90mm wide. A flexure unit is lowered centrally between two supports on which the cookie rests, measuring the force needed to bend or snap the product, Figure 1 shows typical results of a test. As the test progresses, the force imparted increases steadily as the cookie resists breaking. However, at a force of nearly 1,200 grams, the cookie snaps and the force rapidly sinks again as the flexure unit encounters no more resistance.
This test is a valuable tool for product development as it can show the impact recipe alterations can have on texture, for example the inclusion of chocolate chips affecting structure. A texture analyzer could be used to compare the bend properties of chocolate chip and plain cookie samples, or the effects of recipe alterations. Important applications also exist in quality control and in gauging shelf life – determining the consistency and durability so that the consumer will always receive the anticipated ‘snap’ from a cookie.
Reduced fat foods
Texture analysis has become increasingly important in the flourishing low fat and reduced-calorie food markets. Fat is the ingredient often responsible for the pleasant mouthfeel in products such as chocolate, creamy dips and pâtés and where it has been removed, they can become watery or too firm and can also suffer from a loss of flavor. Texture analysis enables food processors to assess the impact of fat reduction and select ingredients and/or processes which best restore good mouthfeel.
A typical penetration test carried out on two pâtés (figure 2) highlights important differences in texture. The negative region of the graph, produced on probe return, indicates the adhesive property of the pâté and/or a certain amount of product adhering to the probe. The reduced-fat pâté requires more force to penetrate and therefore indicates a firmer consistency than its full-fat counterpart.
A simple but reliable way of measuring the crispiness of breakfast cereals is compressing them in bulk with a flat plunger. Test results show multi-peak jagged curves: each peak corresponding to the fracture of an individual flake, which would be perceived in the mouth as a crispy texture. However, one of the issues consumers face with cereals is the rapid degradation of these crispy characteristics when they have been submerged in a liquid. Using the normal procedure, it would be necessary to prepare the sample, then move it to the texture analyzer after draining the liquid, and commence the test.
However, using a watertight plate will minimize the disturbance to the prepared sample and eliminate the delay between immersion and the beginning of the test. A watertight base allows immersion for a defined period of time, after which the base plate can be lowered to drain the liquid.
Precision engineering for quality
The importance of texture in food product development cannot be overlooked. From the impact that texture has on a consumer’s overall enjoyment of food to ensuring a consistent experience with every purchase, texture analysis ensures food manufacturers are able to deliver quality products to consumers.
About Stable Micro Systems
Stable Micro Systems is a leading designer and manufacturer of texture analysis equipment. These instruments are already used in laboratories worldwide for testing in food, packaging, pharmaceuticals, personal care, paints and coatings and other manufacturing industries.