Understand the role of cell structure, phase behavior in the sensation of crispness.

Crispness and crunchiness are extremely important textural properties found in dry and porous cereal products. Consumers often judge the quality of these products based on their perceived crispness. While a lot of progress has been made in determining the factors that affect the crispness of foods, there is a need for a systematic study of complex material properties, including the structure-crispness relationships that exist in cellular foods.

Scientists at Rutgers University conducted a quantitative study of the structure-texture relationship to see how the structure of cellular foods affects their mechanical properties and crispness. Their ultimate goal was to generate systematic information on the physical origins of sensory crispness. This would be done by elucidating the effects of phase behavior and the structure of cellular foods on crispness.

Investigators produced cellular foods that exhibited a range of physical structures. They used extrusion processing, varying extrusion parameters and the chemical composition of the materials. The resulting products were characterized in terms of cell size distribution and cell wall thickness, bulk density, porosity, crystallinity and glass transition (Tg). The deformation and fracture behavior of extrudates during uniaxial compression was analyzed by calculating the number of peaks, the ratio of linear distance and fractal dimensions as a function of phase-state behavior.

Cellular structures with uniform cell size and thin and glassy cell walls had high fractal dimensions and were perceived as very crispy by sensory panels consisting of 10 university students. Such samples had jagged force-deformation curves with sharper and more numerous peaks. As the cell walls became softer, by undergoing a Tg as determined through state diagrams, the products became ductile. Crispness was lost, even when cell size was uniform, and cell walls were thin. Correspondingly, the force-deformation curves lost their jaggedness.

Investigators determined that there exists an interrelationship between the structural, mechanical and sensory properties of crispy materials. Understanding this relationship will be valuable in helping scientists design and develop products.

Further information. Jozef Kokini, Department of Food Science, Rutgers University, Center for Advanced Food Technology, 65 Dudley Rd., New Brunswick, NJ 08901; phone: [phone]; fax: [phone]; email: [e-mail].