Food colour appearance measurement in practice

Colour fading from pigment oxidation in fresh meat, the effect of illrrmination on the appearance of orange juice, the effects of varying coffee and milk concentration on coffee appearance and measuring breakfast cereals by grinding to a defined particle size are given as examples of the types of problems encountered in food colour appearance measurement. The effect of the illuminant on the calculated CIELAB colour values for a variety of food spectra is also presented. 

The ICS Micro Match spectrophotometer used to measure these samples is equipped with the option of using alternative illuminants to calculate CIELAB. The estimated changes in meat colour attributable to different illuminants after one and four days exposure (Table 3.2) illustrate the effect that light quality has on lightness, hue and chroma. The changes in colour produced by the differences 

Storage time AA AWWF Difference ANFL in colour from D65 ACWF A83 A84 

Tungsten lamp A, fluorescent lamps WWF, warm white NFL, natural CWF, cool white 83, triband at 3000° K 84, triband at 4000° K. 

Translucent suspensions are difficult to measure, and direct nnobserved interpretation of instrumental data can lead to confusion because of the way the incident light is dispersed in the sample. Most consistent results are obtained if the instrument aperture is large relative to the incident beam (Kent 1987 MacDougall 1987). The effects of optical geometry on colom and the Kubelka-Munk absorption K (mm ) and scatter S (nun ) coefficients for orange juice were studied by MacDougall (1983) who foimd Too, the luminous reflectance at calculated infinite thickness, increased by 50 per cent if the aperture diameter was increased from 2 cm to 5 cm while the incident beam was maintained at 1 cm. 

---