10.0–30.0g portions of oven-dried samples were placed into a flask (made specially for this purpose, from Gorsuch [20]) and concentrated nitric acid (5ml of acid for 10.0g of dried fruit) was added and heated, with stirring, for 30min. Then, a mixture of nitric acid–hydrogen peroxide (1C1) (for 10.0g of dried sample, 20ml of mixture) was added. The mixture was digested, with stirring, until a clear digest was obtained (approximately 4.0h). Then, the clear digest was diluted to 150ml with distilled water. A blank digest was carried out in the same way.