Determination of flavonoids in fruit and vegetable residues with their application as a potential functional food ingredient

This study aimed to determine the content of quercetin, rutin and isoquercitrin in by-products of certain fruits and vegetables sold in northeastern Brazil and propose their use as functional ingredients in food production. Skins from avocado (Persea americana Mill.), acerola (Malpighia emarginata DC.), beet (Beta vulgaris L.), cajarana (Spondias dulcis Parkinson), yellow and red onion (Allium cepa L.), guava (Psidium guajava L.), kiwi (Actinidia deliciosa (A. Chev.) E. F. Liang and A. R. Ferguson), seriguela (Spondias purpurea L.) and umbu (Spondias tuberosa Arr. Cam.) were freeze-dried and subjected to extraction with organic solvents. The extracts obtained were analysed for selected flavonoids using high-performance liquid chromatography. The highest levels of quercetin were found in red onion (19 836.11 mg center dot kg-1), yellow onion (4 917.11 mg center dot kg-1), acerola (60.28 mg center dot kg-1) and umbu (55.98 mg center dot kg-1). Rutin had high contents in cajarana (4 198.46 mg center dot kg-1), umbu (3 265.37 mg center dot kg-1), acerola (1 538.29 mg center dot kg-1) and yellow onion (1 362.91 mg center dot kg-1). Isoquercitrin was found only in red onion (1 475.76 mg center dot kg-1), acerola (388.46 mg center dot kg-1), guava (295.37 mg center dot kg-1) and umbu (288.91 mg center dot kg-1). The levels of flavonoids found may be sufficient to use them as functional ingredients and fortify certain foods with health-promoting compounds, thereby adding value to food processing waste materials.