*2.9. Colorimetric Determination*

A colorimetric sensor system (LISUN GROUP, CD-200, Kowloon, Hong Kong) was used to determine the color variations of the soap samples at different maturation times. The instrument consists of a D65 light source, a blue LEDs light source and a photoelectric diode detector, and an electronic system for determining the electrical impulses.

The color determination was carried out with the RGB model (red, green, and blue) and the CIELAB color space, which considers the parameters l\*, a\*, and b\* that represent the brightness and the four unique colors of human vision (red, yellow, green, and blue) [26,27].
