Abstract:

Tempeh is a fermented food originated in Indonesia. Its nutritional quality depends on the extent of mycelial
growth on its surface. A method based on image analysis was proposed to determine the fermentation end-point
automatically, quickly, reliably and non-destructively. Tempeh's surface images were collected by using a digital camera
during its fermentation process and a new uniformity evaluation of tempeh’s surface image was formulated through analysis
of texture features and combination of gradient and luminance information. The indicator reached the minimum value at the
fermentation end-point (22 h, determined by sensory evaluation) and showed a significant change near the fermentation endpoint.
When the pixel of tempeh’s surface image was 2592 × 3314, the indicator's value was 0.054 at 21 h, 0.044 at 22 h
and 0.055 at 23 h. However, no significant change was observed in the traditional uniformity evaluation of tempeh’s surface
image (standard deviation of luminance) in which the values were 8.3 at 21 h, 8.2 at 22 h and 8.2 at 23 h. The experimental
results showed that the method could quickly and accurately determine tempeh’s fermentation end-point based on surface
images with different pixels, had a good stability and was consistent with artificial sensory evaluation.

Key words: image analysis, gradient, luminance, tempeh, fermentation end-point