Shining a Spotlight on Physical Food Testing
Most of us have had an unpleasant experience with the physical qualities of our food. Perhaps you’ve encountered cookies that are too soft or too crunchy, clumpy beverage powders, or jarred sauce that looks just plain unappetizing.
These foods may taste delicious and provide plenty of nutritional benefits, but if they aren’t appealing and consistent in their physical attributes, consumers may remember their bad experience and avoid making a repeat purchase. Both appearance—the extent to which food looks appealing—and taste—the extent to which consumption of food is appealing to the senses—have been identified as food values that are likely to predict why consumers choose certain food products over others.
Physical food testing ensures that your products are consistent and appealing in variables such as color, viscosity, and texture, which plays a role in taste. It may seem difficult to measure these attributes for quality and consistency, but a good physical food testing lab will have the resources you need to get accurate results. These are the physical food testing measures every food industry professional needs to understand.
Physical Food Testing
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Color Appearance Tests
If the physical appearance of a product looks unappetizing or inconsistent with previous food purchases from the same brand, a consumer may assume the worst about the product’s taste or safety. Controlling the color of both incoming ingredients and the finished product can be critical to the success of a product.
The L,a,b color scale mimics the human eye’s perception of color and defines color appearance in ways that can be readily understood. Two industry-standard instruments, the Hunter and Minolta instruments, both offer color analysis using the L,a,b scale.
Several color appearance tests are available for special situations, such as the Lovibond method, the standard for measuring the color of refined oils and shortenings. Other options for measuring color include spectrophotometric methods and industry-standard methods for spices that are published by the American Spice Trade Association (ASTA).
Objective Texture Testing
Texture can make a big impact on a consumer’s perception of taste, but it seems impossible to conduct a high-quality test on such a seemingly subjective variable. Luckily, there are several objective texture tests available to help.
Physical food properties can affect the quality of your product in countless ways, from the quality of the wheat and flour used, to the way your product reacts to different temperatures.
Various instruments have been developed over the years to produce accurate texture testing for specific products, such as the Penetrometer for pastes and soft solids and the Kramer shear press for peas and other vegetables. These days, more universal testing methods are also available, including the Instron Universal Testing Machine and a unique texture analyzer from Stable MicroSystems, which uses test probes and fixtures to analyze a wide range of food products.
Accurate texture testing with any instrument requires taking several samples and determining the average to obtain a representative result—mixing or homogenizing the sample will alter the texture and skew your results. Be prepared to deliver a larger sample than you may have expected so that you can obtain a true representative sample.
Viscosity, or the ease with which a liquid flows, plays a big part in consumers’ perception of your product. Not only can viscosity affect texture, it may also make your product appear to be high or low quality if the viscosity is thicker or thinner than consumers expect.
There are several types of instruments that empirically measure an index of viscosity:
- Botswick Consistometer (widely used in the tomato industry)
- Bloom Gelometer (used to analyze gelatin gel strength)
- Brookfield (a versatile tool that comes equipped with standard straight spindles, T-bar spindles, low-volume accessory, and low-viscosity accessory)
These tools are all helpful in analyzing viscosity, but accurately measuring the complex flow properties found in food can require instruments that use more sophisticated techniques. For example, the modern controlled stress rheometer is used to measure fundamental rheological properties of a liquid. Labs using controlled stress rheometers can use this detailed analysis to uncover process control issues and product texture problems.
Another issue relevant to viscosity is temperature. Many liquids become more or less viscous at different temperatures, making it an important variable in your process. The Haake rheometer features a precise temperature control system that allows samples to be heated or cooled at programmed rates. This results in an accurate measure of viscosity as as a function of temperature.
Other Types of Food Analysis
Physical food properties can affect the quality of your product in countless ways, from the quality of the wheat and flour used, to the way your product reacts to different temperatures. These test capabilities should be part of any physical food testing lab.
Particle Size Analysis
Particle size testing is useful when analyzing powders, emulsions, pastes, suspensions, and creams. Traditionally, particle size is measured with instruments like the Rotap Sieve Shaker, which uses sieves with a variety of mesh sizes. A different instrument, The Alpine Jet Tester, can also be used to prevent sticky powder samples from clinging near sieve openings and preventing accurate results.
A laser diffraction instrument, such as the Microtrac SRA 150, is a newer option for determining particle size. In this type of testing, particles are dispersed in a compatible liquid that won’t cause the particle to dissolve or agglomerate. This allows much smaller particles to be sized than the traditional sieve method—the Microtrac SRA 150 can define particle size distribution ranging from 0.7 to 700 micrometers.
Your product could be exposed to a variety of temperature changes in the journey from shipping to stocking on store shelves. The most common test in the food industry is Differential Scanning Calorimetry (DSC). DSC is a widely used technique that can accurately measure freezing points, melting points, and percent of freezable water.
Another technique, called the Thermo-Gravimetric Analysis (TGA), is less used in the food industry but still yields valuable results. It measures the weight change of a sample while heating or holding at a constant temperature. The rates of moisture loss at various temperatures can shed light on the free vs. bound water content of the sample.
Wheat and Flour Quality Tests
A wide range of methods and instruments have been developed to test the properties of flour, many of them published by the American Association of Cereal Chemists (AACC). Here are a few of the most common options:
- The Brabender Farinograph measures the amount of water required to make dough of optimum consistency, as well as the mixing time required to reach this consistency.
- The Brabender Amylograph can measure peak viscosity, levels of fungal enzymes, gelatinization temperature, breakdown rate after gelatinization, and viscosity setback upon cooling.
- The Glutomatic gluten quality analyzer provides a quantitative measure of gluten.
- “Viscosity of Acidulated Flour-Water Suspensions” is a test that measures the relative gluten strength in soft wheat flours.
- The "Solvent Retention Capacity" method has newly been adopted by the AACC as a way to measure the liquid-holding capacity of flour in four different solvents, thereby predicting flour performance in different baking applications.
Moisture Sorption Isotherms
Analyzing moisture sorption isotherms allows packaging engineers to define the moisture barrier requirements of the packaging needed for maximum shelf life of the product. It can also help you determine the compatibility during storage of different ingredients or components in a mixed system. This food testing method involves plotting the equilibrium moisture content of a sample as a function of relative humidity.
Creating High-Quality Products with Physical Food Testing
There’s no need to tell you how vital it is to invest in quality physical food testing before bringing a product to market. If consumers have a bad experience with a product due to its appearance, texture, or viscosity, you could be faced with falling sales numbers.
It may seem difficult to accurately analyze the many physical attributes of your food product, but these reliable tests are up to the challenge. Check out our blog post “How to Build a Quality Management Program for Your Lab” to learn more about how best practices in analytical food testing labs can improve your overall product.
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