Bioactive compound content in special pigmented wheat varieties: the effect of pearling, environment and agricultural practices.

Cereals are an important source of bioactive compounds and some of them, such as polyphenols, show a remarkable antioxidant activity (1). Increasing evidence from clinical and epidemiological studies suggest that the regular consumption of wheat as whole grain and whole-grain products might reduce the risk of chronic pathologies such as cardiovascular diseases (2). Pigmented wheat varieties, rich in phenolic compounds and carotenoids, could be an interesting source of functional ingredients to enrich the nutritional value of bakery products. The aim of this study was to evaluate the nutritional value and the presence of bioactive compounds in a wide array of edible wheat grains (Triticum aestivum L.). Blue (cv. Skorpion), purple (cv. Rosso), yellow (cv. Bona Vita) and white (cv. Whitebear) wheat grains were compared to a control red ordinary variety (cv. Aubusson and PR22R58), considering different environments and the application of different crop practices (nitrogen fertilization and fungicide application). Moreover, the study was focused on the distribution of bioactive compounds in different kernel layers: six pearled fractions of the kernels (0-5%, 5-10%, 10-15%, 15-20%, 20-25%, 25-100%) were obtained through the incremental pearling of the five wheat varieties (3). Total dietary fibre (DF), -glucans, proteins, ashes, free and bound phenolic acids, alkylresorcinols, anthocyanins, carotenoids and total antioxidant activity (TAA) were analyzed for each fraction. Considering different environmental and agricultural conditions, the grain yield and protein content of the special pigmented varieties resulted comparable to the reference variety. Significant differences (P<0.05) were observed for the bioactive compounds content among wholegrain flour of the varieties except for the DF and the TAA. Proteins were on average mainly concentrated in the intermediate kernel layers (from 10-15% to 20-25%) in all the varieties, while the concentration decreased towards both the internal and the external layers. The 0-5% fraction showed the highest total DF content in all the varieties. In each successive pearling step towards inner layers, the DF content significantly decreased (P<0.05). -glucans were on average mainly concentrated in the intermediate kernel layers corresponding to the second and the third pearled fractions. On average TAA, free and bound phenolic acids showed higher values in the outer layers of the kernel and decreased at each pearling passage, while alkylresorcinols were mainly concentrated in the second pearled fraction. The purple variety showed a concentration of total anthocyanins about 40% higher than the blue one and different profiles in anthocyanins were observed between the two varieties. Delphinidin-3-O-glucoside and delphinidin-3-O-rutinoside were detected only in the blue variety. On the contrary, peonidin-3-O-glucoside was detected only in the purple variety. Moreover, even though significant differences (P<0.05) were observed within both varieties after each pearling passage, anthocyanins showed a different distribution depending on the variety. In the purple wheat anthocyanins were mainly concentrated in the outer layers (0-5 % fraction) with a significant decrease (P<0.05) towards the inner layers. On the contrary, the blue variety showed the highest anthocyanin content in intermediate layers, corresponding to the 10-15% fraction, and a significant decrease (P<0.05) was observed towards the inner and the outer layer of the kernel. Special pigmented varieties could be a good raw material for the development of dedicated supply chains for the production of flour characterized by high levels of bioactive compounds. Moreover, since the bioactives are mainly located in the intermediate grain layer, the pearling procedure could be employed for these varieties in order to select specific pearled fractions that might be used as functional ingredients, valorizing the external kernel layers usually removed in the classic milling process.