DOI: 10.34894/ouurrh
title: Tristimulus colorimetric pigment prediction in food: a review

description: Carotenoid and anthocyanin pigments are responsible for a large range of fruit and vegetable colour (carotenoids: yellow to red; anthocyanins: red to purple-black). The colour of food is suggested to stimulate appetite and digestion and has been reported as an indicator of fresh produce quality for consumers. Importantly, their relatively unstable chemical structure makes the both pigment groups potent antioxidants when consumed in the diet. 
Colorimetric analysis is proposed as a non-destructive method to estimate carotenoid and anthocyanin content in different foods, a more accessible aid and/or alternative to traditional chemical assays (eg., high-performance liquid chromatography, spectrophotometry, etc.). Colour can be measured quantitatively with tristimulus colorimeters or digital image analyses via standardised three-dimensional colour spaces (eg., CIELab/Ch, RGB) and their individual colour parameters. However, the results of current literature in the field of colorimetric pigment prediction are inconsistent. Therefore, a literature review was performed to report and compare the current findings in the field of colorimetric prediction of carotenoid and anthocyanin content in different kinds of foods.
description: Pigment analysis optimisation
description: Review of tristimulus colorimetric carotenoid prediction original studies (n = 22), publication year range: 1969–2020; tristimulus colorimetric anthocyanin prediction original studies (n = 9), publication year range: 1991–2025. Metadata extracted from all studies are: DOI identification ("DOI"); authors; article name; publication year ("Year"); peer-reviewed journal publisher ("Journal"); H-index (as of 2024); primary and secondary research objectives ("Objectives"); method of pigment quantification ("Quantification"); tristimulus colorimetry, pigment quantification, and statistical analysis methodology steps ("Methodology"); sample size; variety of food analysed, macrofood reported within parentheses ("Variety"); relevant sample details ("Sample Details"); relevant pigment quantification, tristimulus colorimetry, and statistical results ("Results"); explained variance in percentage for pigment-content correlations, separated by colour parameter and pigment group ("r² (%)"); confidence interval in percentage ("CI (%)"); relevant colour-pigment conclusion ("Conclusion (colorimetry analysis focus)"); and extra observations. 
Colour parameters from the CIELAB/Ch colour space recorded: L* or L (lightness); a* or a (redness); B* or b* or b (yellowness); C* (chroma); h° (hue angle). 
Abbreviations used in the metadata table include: T. colorimetry (tristimulus colorimetry); quantif. (pigment quantification); stats. (statistical analysis); TCC (total carotenoid content); TAC (total anthocyanin content); 3-G (3-glucoside); HPLC (high-performance liquid chromatography); RGB (red, green blue colour space); UV-Vis (UV-visual); PCR (polymerase chain reaction); FW (fresh weight); DW (dry weight); R (Pearson's correlation coefficient); r² or R^2 (explained variance); PLS (partial least squares); PCA (principal component analysis); RMSEP (root mean square error of prediction); ANOVA (analysis of variance); NDAI (normalised difference anthocyanin index); CIRG index (colour index for red grapes); LOD (limit of detection); provitA (provitamin A); BHT (butylated hydroxytoluene); THF (tetrahydrofuran); KCl (potassium chloride).
description: Data will be provided under request.