Not the Sound of Silence Neil H. Mermelstein | December 2013, Volume 67, No.12

FOOD SAFETY & QUALITY

A researcher records force and sound simultaneously.The sound a food makes when it is being consumed is an important sensory factor influencing consumer acceptance of a product. Much research has been conducted over the years on measuring the sound a food produces as it is being chewed and correlating it with results of sensory evaluation. The scientific study of food sounds essentially began in the early 1960s with work by Birger K. Drake, who was reportedly the first to deal seriously with measuring the sound of food, and continued with work by Zata Vickers and others in the late 1970s and early 1980s and work by Charles Spence and others in recent years.

Zata M. Vickers, Professor, Dept. of Food Science and Nutrition, University of Minnesota, conducted a series of research studies on the relationship of chewing sounds to crunchiness and crispness of foods. She demonstrated that crisper foods produce louder and higher-pitched sounds than less-crisp foods. She recorded the sound produced as the panelists bit into food and then played it back. She studied various placements of the microphone to determine the best location and found that she obtained the right balance of sounds when she pressed the microphone to the head just above the ear canal. As the front teeth bite food, she said, sound passes through the air, if the mouth is open, through the bone, which resonates and amplifies lower pitches, and through the soft tissue, which dampens the higher-pitched sounds.

Charles Spence, Professor, Dept. of Experimental Psychology, University of Oxford, has been conducting research on the influence of sound, color, shape, and other factors on consumers’ perceptions of foods. He has been using a variety of techniques in his research, including audio recording, human psychophysics, functional magnetic resonance imaging (fMRI), electroencephalography (EEG), and transcranial magnetic stimulation (TMS). He said that this exciting new area of research, which falls under the heading “neurogastronomy,” is changing the way scientists view the five senses and contributing important new insights to the understanding of the brain. The findings of this research have implications in many areas, he said, from the design of interfaces to improving the flavor of food.

Spence has researched how understanding multisensory perception can be used to improve people’s perception of foods. He and his coworkers have shown, for example, that panelists’ perception of the crispness of potato chips can be affected by modifying the sounds produced as they bite them and playing them back during the tests. They demonstrated that the perception of both the crispness and staleness was systematically altered by varying the loudness and/or frequency of the auditory feedback elicited during the biting action. The potato chips were perceived as being 15% crispier when either the overall sound level was increased or just the high-frequency sounds were amplified. This has implications for enhancing consumers’ eating experiences in restaurants. Many restaurants are so loud patrons can’t hear themselves think, he said, and this research implies that they probably can’t taste either.

Spence is now working in the area of food delivery devices, such as packaging, and the sounds they make. For example, Frito-Lay’s SunChips® biodegradable package made such a loud crinkling sound when handled even gently that the company withdrew it from the shelves. Spence also sees possibilities in enhancing the sound of food using technology and in developing new packaging that can enhance the consumer’s experience of a product. With regard to what’s ahead, he sees a huge explosion of interest in matching soundscapes and music to flavor and texture experiences.


Adding Sound to Texture Testing

The texture of foods has traditionally been instrumentally determined by measuring the force needed to compress a food until it fails (e.g., until a cracker breaks) and correlating the results with sensory evaluation. Recently, sound recording has been added to the instrumental testing. Marc Johnson, President, Texture Technologies Corp. (www.texturetechnologies.com), the North American distributor of instruments manufactured by Stable Micro Systems Ltd. (www.stablemicrosystems.com), said that Texture Technologies Corp. has worked on texture testing instruments and fixtures since 1988.

Johnson said that as food products such as breakfast cereals, potato chips, and extruded snack foods are crushed or penetrated by the instrument’s probes, the system quantifies the products’ force profile. Sharp drop-offs in force occur when the product’s structure fails. Sounds are also produced during the tests, and Stable Micro Systems developed a method of measuring the acoustic energy released. In 2002 the company added acoustic analysis capability to its workhorse instrument, the TA.XTplus Texture Analyzer, and a few years later added an extremely high-quality, calibrated microphone to create its Reference Acoustic Envelope Eetector (RAED), which captures sound in calibrated decibels and synchronizes it with traditional force-based instrumental measurements of texture. The RAED connects to the TA.XTplus, which then generates synchronized force and sound profiles.

Sound-profile curves often add additional metrics about a product’s crispy-crunchy behavior that cannot be easily picked up in the force profile, Johnson said. By analyzing sound simultaneously with forces, companies can very precisely quantify the behaviors they are designing into their products. The RAED has high sensitivity to the frequencies emitted by brittle products, he said, but low sensitivity to mechanical noise emitted by the texture analyzer itself. It includes a frequency filter that removes ambient vocal and machine noise from the acoustic signal and thus allows tests to be conducted even in relatively exposed environments, such as R&D lab benches. Recent improvements/enhancements to the texture analyzer, he added, have included use of improved electronics and filters, high-quality microphones, and high-definition cameras.

The company has conducted application studies on foods such as French fries and wheat crackers. Capturing tests on video, complete with sound, Johnson said, shows how test products fracture and can therefore be very useful in product development. The acoustic profiles can be used to evaluate new formulations and processes, ingredient substitutions, moisture-migration concerns, packaging quality, and shelf life. Johnson said that using consumer panels to evaluate products is expensive, so the system can be used to evaluate different treatments and formulations before moving on to consumer panels.

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