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The acoustic emission (AE) technique was used to develop a method for the objective evaluation of the crispness of porous foods. The crispness of six types of commercial porous foods was changed by controlling their moisture contents at six levels by varying the humidity (i.e., dry, 22, 43, 56, 68, and 81 % relative humidity) of the storage environment at 25 °C. As the crispness of a sample with high water activity (a w ) was expected to deteriorate, the physicochemical, mechanical, and acoustic characteristics of a w -controlled food samples were evaluated. The a w had no influence on the shape and porous structure of the foods. However, the number of force peaks in the uniaxial compression test appeared to be related to their a w . Moreover, the breaking characteristics of a sample at different a w values changed depending on the porous food type classified according to the degree of starch gelatinization. Among the AE characteristics, the number of AE events and AE count corresponded well with the a w of the porous food. Therefore, for an objective evaluation of the crispness of porous foods, the AE events and AE count, which are highly sensitive, can be suitable indicators, rather than the number of force peaks.

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A method to obtain clear binary images of bread crumb grain has been developed from the viewpoint of image synthesis, and named 'Multiple Binarization Imaging Method (MBI).' Nine thresholds were formally selected from a brightness histogram with gray-levels. The object image was synthesized (logical add) from nine intermediate binary images with each threshold after eliminating unnecessary image element. The aim of this study is to examine the MBI method using breadcrumb simulated boards which had holes with constant diameter (. mm) and various depths (.. mm), and those with constant depth (. mm) and various diameters (.. mm). Brightness value of a hole is considered to be correlated to the depth of the hole. However, the hole diameter could not be identified from brightness value histogram with gray-levels. Therefore, it was suggested that the number of thresholds which should be set did not depend on the hole diameter and the number of patterns of hole depths, but that it was derived from the fact that the gray image of air hole images had classes. The MBI method yielded good and consistent binary images of crumb air bubbles of commercial white bread. Open-top type bread had coarser crumb structure with vertically orientated at the central area of the crumb. Pullman-type bread had finer porous structure without orientation at the central area of the crumb.