Ultra-performance liquid chromatography (UPLC) quantification of carotenoids in durum wheat: Influence of genotype and environment in relation to the colour of yellow alkaline noodles (YAN)

Carotenoids are the main compounds responsible for the yellow colour of durum wheat semolina and flours. However, the concentration of carotenoids in wheats depends on genotype and growing environments. The total pigment and carotenoid concentration of four durum wheat varieties (AC Avonlea, Commander, AC Navigator and Strongfield) and two common wheat varieties (AC Barrie and AC Snowbird), which were grown in different locations in Saskatchewan, Canada (Taber, Regina and Swift Current), were determined using the AACC International approved method and ultra-performance liquid chromatography (UPLC). A fast (within 6 min) and sensitive method for separation of carotenoids extracted from durum wheat flours was developed using UPLC. The results show that Commander and AC Navigator varieties exhibited higher total pigments and lutein concentration than the other wheats. Wheat grown in Taber and Swift Current regions had higher total pigments and lutein concentration than those grown at Regina. Although carotenoids in wheat extracts possessed antioxidant properties there was no significant correlation between antioxidant capacity and the concentration of carotenoids in the extracts (r2 = 0.13). The carotenoid extracts from AC Barrie exhibited the highest DPPH radical scavenging, while AC Avonlea showed the lowest. The concentration of extracted lutein highly correlated (r2 = 0.93) with the yellowness, b* value, of the yellow alkaline noodles, whereas the correlation between lutein concentration and noodle redness, a*, or brightness, L*, values were not as strong (r2 = 0.75 or 0.58, respectively). Thus, the high concentration of lutein in the durum wheats contributes to the desirable greater yellowness of yellow alkaline noodle, an important key to making a healthy yellow alkaline noodle without artificial yellow agent.

Research highlights
► A fast and sensitive method for separation of carotenoids extracted from durum wheat flours using an UPLC within 6 min was developed.
► Amounts of carotenoids in Canadian durum wheats depend on genotypes and growing conditions.
► The total pigment content is highly positively correlated with amounts of lutein in wheats (r2 = 0.96).
► The total pigment is strongly, positively correlated with the b∗ values of noodle color (r2 = 0.96).