Optimization of Sponge Cake Added with Turmeric (Curcuma longa L.) Powder Using Mixture Design

This study examined the optimal ingredient mixing ratio for the preparation of sponge cake containing turmeric powder. After preliminary studies, the following ingredient ranges were determined: 116.0-129.5% sugar, 0.5-5.0% turmeric powder, and 10.0-23.5% oil. Among the different mixture designs, the D-optimal design was chosen for analysis. Linear models were applied to determine the color values of lightness, redness, and yellowness, as well as textural values for hardness, gumminess, and chewiness. A quadric model was used to determine all the categories in the sensory analysis. The fitness analysis results showed that in all the sensory characteristics, the probabilities were significant within 5%; thus, the models were accepted as appropriate. The response surface and trace plot results showed that increasing amounts of turmeric powder decreased the brightness, and increased redness and yellowness. In addition, increasing amounts of turmeric powder caused an increase in the hardness, gumminess, and chewiness, and thus the softness of the cake decreased. Cake samples received low sensory evaluation scores when sugar, turmeric powder, and oil were added above their optimal levels. In the numeric optimization analysis, the optimal ingredient amounts were 123.4% sugar, 1.6% turmeric powder, and 14.9% oil. The above results demonstrate the feasibility of adding turmeric powder to sponge cake. Thus, the commercialization of a turmeric sponge cake marketed as a functional food was deemed possible.