Wheat flour granulometry determines colour perception

Einkorn, durum wheat and Kamut® are rich of carotenoids, antioxidants with beneficial effects on human health. In the present study the effect of flour granule size on carotenoid content and colour was assessed; furthermore, the suitability of two colorimeters (Minolta Chroma meter CR-210 and Minolta Chroma meter II Reflectance), a spectrophotometer (Jasco V-650 with integrating sphere) and image analysis to define colour and determine carotenoids concentration in wheat flours of different granulometry was tested. Carotenoid content did not vary across flours of diverse size, except in the finest einkorn fraction (<80 m), which had lower concentration. For all instruments colour coordinate L* decreased and b* increased with flour size growth, while a* varied with the different devices. A Principal Components Analysis (PCA), performed considering carotenoid content and all colorimetric indices, distinguished einkorn from durum and Kamut®, and divided samples of different granulometry; a similar result was achieved by a PCA performed on the absorbance spectra from the integrating sphere. The PCA on image texture data classified the samples following flour size. In conclusion, flour colour is determined not only by carotenoid content but also by flour particle size: therefore, direct colour measurement seems not suitable to predict flour carotenoid content.