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.Mean magnitudes of all frequency ranges in the power spectrum wereclosely correlated with structure.Additionally, in subsequent investigations bothfracturability indices were found to be strongly correlated with fitted parametersof Eq.(14) (25), indicating that all three methods are consistent in providing areliable measurement of relative fracturability.Figure 8 Dependence of sensory crunchiness and sensory density on power spectrumparameters and fractal dimension.(From Ref.13, p.89.With permission.)Copyright 2003 by Marcel Dekker, Inc.All Rights Reserved. The physical basis for the dependence of fracturability on structure is analo-gous to that for strength cellularity relationships.A relatively dense structurewith thick cell walls can withstand relatively greater stress prior to failure andcan be expected to fail with fractures that are individually of higher intensity.Asmall-celled product, with a relatively greater number of cell wall supports, mightexpectedly fail with a higher frequency of fracturing although for such veryinterconnected structures, many fractures may extend throughout large subunitsof the structure.Fracturability, and sensory attributes such as crunchiness thatdepend on fracture behavior, can thus be tailored by adjusting and optimizingthe two physical properties.In fact, subjective attributes have been shown to depend on fracture behav-ior, as demonstrated by positive relationships between pertinent sensory proper-ties such as those between perceived crunchiness or perceived denseness andeither fractal dimension or mean magnitude of the power spectrum (13) (Fig.8).Such correlations between sensory attributes and mechanical properties, andthose between failure behavior and structure, can be used as predictive tools fordesigning extruded foods with specific, desired characteristics.VI.OTHER POROUS-STRUCTURED FOODSThe relationships between mechanical or textural properties and structure ob-served for extrudates are potentially applicable to other brittle-porous products,such as baked flat breads, crackers, and popcorn.Furthermore, many bakedgoods, while plastic, are cellular and therefore subject to similar relationshipsbetween mechanical strength and structure or between mechanical properties andtexture.Such correspondence between structure, failure properties, and function-ality provides a convenient means of tailoring foods to possess desired attri-butes and acceptance.ACKNOWLEDGMENTThis work was supported by the U.S.Army SBCCOM, Natick Soldier Center,and was conducted as part of ration research and development efforts.REFERENCES1.Alvarez-Martinez, L., Kondury, K.P., and Harper, J.M.1988.A general model forexpansion of extruded products.J.Food Science 53(2):609 615.2.Launey, B., and Lisch, J.M.1983.Twin-screw extrusion cooking of starches: flowCopyright 2003 by Marcel Dekker, Inc.All Rights Reserved. behavior of starch pastes, expansion and mechanical properties of extrudates.J.FoodEngineering 2:259 280.3.Hicsasmaz, Z., and Clayton, J.T.1992.Characterization of the pore structure ofstarch-based food materials.Food Structure 11:115 132.4.Barrett, A.H., Ross, E.W., and Taub, I.A.1990.Simulation of the vacuum infusionprocess using idealized components: effects of pore size and suspension concentra-tion.1990.J.Food Science 55(4):989 993.5.Barrett, A.H., and Ross, E.W.1990.Correlation of extrudate infusibility with bulkproperties using image analysis.J.Food Science 55(5):1378 1382.6.Gibson, L., and Ashby, M.F.1988.Cellular Solids.New York: Pergamon Press.7.Moore, D., Sanei, A., Van Hecke, E., and Bouvier, J.M.1990.Effect of ingredientson physical/structural properties of extrudates.J.Food Science 55(5):1383 1387,1402.8.Russ, J.C., Stewart, W.D., and Russ, J.C.1988.The measurement of macroscopicimages.Food Technology, February:94 102.9.Gao, X., and Tan, J.1996.Analysis of expanded food texture by image processing.J.Food Process Engineering 19:425 456.10.Tan, J., Gao, X., and Hseih, F.1994.Extrudate characterization by image processing.J.Food Science 59(6):1247 1250.11.Smolarz, A., Van Hecke, E., and Bouvier, J.M.1989.Computerized image analysisand texture of extruded biscuits.J.Texture Studies 20:223 234.12.Barrett, A.H., and Peleg, M.1992.Cell size distributions of puffed corn extrudates.J.Food Science 57(1):146 149, 154.13.Barrett, A.H., Cardello, A.V., Lesher, L.L., and Taub, I.A.1994.Cellularity, me-chanical failure, and textural perception of corn meal extrudates.J.Texture Studies25:77 95.14.Cohen, S., Voyle, C., Harniman, R., Rufner, R., Barrett, A.H., and Hintlian, C.1989.Microstructural evaluation of porous nutritional sustainment module extrudates.U.S.Army Natick RD&E Center Technical Report, TR-89-034.15.Barrett, A.H., and Peleg, M.1995.Applications of fractal analysis to food structure.Food Science and Technology 28:553 563.16.Barrett, A.H., Kaletunc, G., Rosenberg, S., and Breslauer, K.1995.Effect of sucroseon the structure, mechanical strength and thermal properties of corn extrudates.Car-bohydrate Polymer 26:261 269.17.Kim, C.H., and Maga, J.A.1993.Influence of starch type, starch/protein compositionand extrusion parameters on resulting extrudate expansion.In: G.Charalambous,ed.Food Flavors, Ingredients and Composition.New York: Elsevier Science, pp957 964.18.Faubion, J.M., and Hoseney, R.C.1982.High-temperature short-time extrusioncooking of wheat starch and flour.I.Effect of moisture and flour type on extrudateproperties.Cereal Chemistry 59(6):529 537.19.Fan, J
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