The objective of this work was to evaluate possibilities and restrictions of the color measurement device based on digital camera and image analysis software. The color measurement instrument consisted of a digital camera with zoom-lens combined with computer software for image analysis with plugin programs for color analysis and calibration. This paper will examine color changes in red berry juices. Liquid materials bring challenges to color measurements with their transparency or translucency and glossy surfaces. The aim of this study was first to investigate how the dilution of juices affects the color measured. The aim was also to investigate effects of heat (heating at constant temperatures of 70, 80 and 90 C°) on the color of juices (lingonberry, raspberry) and can these changes be measured by the device used.

Dilution caused significant changes in the measured color coordinates.  Coordinate L* (lightness) increased as the juice concentration decreased.  Color coordinates a* and b* also increased as the concentration decreased in high juice concentrations. However after certain dilution degree (20 % for a* and 40 % for b*) coordinates a* and b* decreased as the juice concentration decreased.

The effect of heat treatment on lingonberry juice color was seen both with measurement device and by visual observation. Although changes in color were only slightly perceptible, the color changes were distinctive in data captured by measurement device. Changes in color coordinates were several units indicating perceptible color changes. Total color changes (ΔE) from unheated samples were 6.82, 10.92 and 11.04 (at temperatures 70, 80 and 90 C° in following order). Also differences between heating temperatures could be detected. Changes in color coordinates and chroma were faster when the temperature was higher because of the faster degradation of berry anthocyanins. On the contrary the effect of heat on the raspberry juice color was very small. Changes in color were hardly perceptible since total color differences were only 2.39, 3.51 and 1.73 units (at temperatures 70, 80 and 90 C°). 

These results indicate that the dilution of juice affects color significantly. The effects of dilution are hard to predict since they depend on the degree of dilution.  When the juice examined is concentrated dilution causes only slight increase of color coordinates. As the concentration decreases changes in coordinates become more significant and also the direction of changes change. One possible explanation is the change of translucency to transparency at small juice concentrations. The results indicate foremost that the dilution of the juice must be standardized if other color changes are examined.

Heating causes color changes in berry juices. Due to the different anthocyanin profiles of berries chosen for this study, the effect of the heat treatment was noticeably different. Based on these results it can be concluded that the color measurement based on digital camera and image analysis software can be used to analyze slight color changes in berry juices during heat treatments.