This study aimed to analyze the effects of the extrusion number on the quality characteristics of Ddukgukdduk and to determine an optimal preparation condition for the production of Ddukgukdduk. Three Graedduk samples were produced by mixing the same amount of rice, water, and salt and extruded two, three, and four times. Ddukgukdduk samples were prepared by cutting the Garaedduk dried for 48 hours at room temperature. For the analysis on the quality characteristics of Garaedduk, water contents were measured by means of a normal pressure heat drying method, and the chromaticity of the Garaedduk was measured using a colorimeter. Physical properties were measured using a Texture Analyser. The micro-structure of the Garaedduk by the number of extrusions was observed using a scanning electron microscope. The water absorption and elution of solids were measured to analyze the quality characteristics of cooked Ddukgukdduk, and its texture was measured using a Texture Analyser. A sensory evaluation of cooked Ddukgukdduk was conducted to research consumer preferences with 75 female college students.

The water content of the raw Garaedduk did not change significantly as the number of extrusions increased. The reason was because raw Garaedduk was not exposed to the cooling water in the production process in this experiment contrary to the normal production process in the industry. In a comparison between the chromaticity of raw Garaedduk and that of Garaedduk dried for 48 hours, L value, a value and b value showed no significant difference by the number of extrusions, which indicates that the number of extrusions does not have a large effect on the chromaticity. The texture analysis of the raw Garaedduk revealed that hardness decreased and adhesiveness significantly increased as the number of extrusions increased. Elasticity and cohesiveness also showed a significant difference, but chewiness showed no significant difference between each sample. The number of extrusions in the rice cake machine was found to have an effect on the texture of the Garaedduk. According to the results of analysis on the micro-structure of the Garaedduk dried for 48 hours, the size of pores became smaller and the pores were uniformly distributed as the number of extrusions increased. Thus, it is determined that the pore size and its uniform distribution would affect the overall quality characteristics of the Garaedduk.

The water absorption and elution of solids were measured to examine the characteristics of the Ddukgukdduk after cooking. The results found that the water absorption lowered significantly as the number of extrusions increased, and the elution of solids showed the lowest value in the sample extruded three times. The sample with large and non-uniform pores exhibited higher water absorption and solid elusion rates than the sample with small and uniform pores due to the great number of extrusions as the starch granules fell out when cooked.

The results of analysis on the texture after cooking confirmed that hardness differed significantly by the number of extrusions, and its value was higher than that before cooking, which is attributed to the aging of rice starch. The adhesiveness was significantly higher as the number of extrusions increased. In the case of elasticity, the sample with the highest number of extrusions showed a significantly lower value than those of the samples with lower numbers of extrusion. There was no significant change in cohesiveness and chewiness. Thus, it is determined that as the number of extrusions increases, Ddukgukdduk become soft and provide excellent chewiness.

The sensory evaluation of cooked Ddukgukdduk showed that the overall acceptability became higher and there was no significant difference in appearance acceptability and colors as the number of extrusions increased. The number of extrusions was found to have an effect on the acceptability with respect to hardness and chewiness. Since the effect on the consumer preferences is an important factor that can lead to the purchase, an increasing number of extrusions is expected to help promote sales. Based on the findings of this study, it is concluded that an increase in the number of extrusions has a positive effect on the quality characteristics of the Garaedduk and Ddukgukdduk.