Anthocyanins in Blue and Purple Wheats: Characterization and Stability Upon Processing
Purple and blue coloured wheats contain significant amounts of anthocyanins. There is a linear relationship between the ash and anthocyanin content of milling fractions, confirming the localization of anthocyanins in the bran layers. Purple wheats contained predominantly cyanidin-3-glucoside, and pelargonidin-3-glucoside, and had an overall complex anthocyanin composition. Blue wheats were enriched in delphinidin-3-glucoside, and a had simpler composition than purple varieties. Sprouting was not a suitable treatment to increase anthocyanin extractability, since it significantly decreased the anthocyanin content. In processed wholemeal products (i.e., crackers and bread), mixing and baking steps significantly decreased anthocyanin content, while resting/fermentation did not. Dough systems with decreased pH were more protective of anthocyanins during intermediate processing steps, as were high-temperature, short-time baking procedures. Purple wheat anthocyanin composition was more affected by mixing, while blue wheat composition was thermally affected. Therefore, bread and cracker procedures can be designed to optimize anthocyanin retention in the final product.