The spectrophotometric determination of tannins in flakes
Iga Rybicka and Justyna Kiewlicz
Poznan University of Economics and Business, al. Niepodległości 10, 61-875, Poznań, POL
Tannins are antinutrients present in different plant-origin food products. They affect both positively (e.g. antioxidant activity) and negatively on the human body. The negative aspect is the exhibition of the absorption of minerals, e.g of magnesium and iron. Flakes are an important assortment in everyday menu and are also a good source of macro- and micronutrients. Therefore, the aim of the study was to determine the content of tannins in a range of flakes available on a Polish market.
Twenty plain flakes from different raw materials and prepared using different technological processes (including puffed, flakes and shredded cereals) were selected to the study. The tannins were determined using spectrophotometric method. 0.1 g of homogenized and dried sample was put into tube and 5 mL of water was added. The closed tube was boiled for 30 min. After cooling, 1.5 mL of supernatant was transferred to Eppendorf tube and centrifuged at 14.000 rpm for 10 min. 0.5 mL of supernatant was added to 0.5 mL of 20% Na2CO3 and 0.25 mL of Folin-Ciocalteu reagent and filled up to 5 mL with water. It was left in dark for 30 min and the absorbance was measured at 700 nm. Each sample was analyzed in triplicate. The standard curves of tannic acid were prepared in a range of 0 – 100 mg L-1.
The results indicated that rye (wholemeal and roasted wholemeal) and spelt (roasted wholemeal) flakes had the highest content of tannins - about 11.5 mg in 1 g of d.m. Significant content of tannins (8-9 mg/g d.m.) was also found in corn flakes (roasted wholemeal), oat flakes (wholemeal and roasted wholemeal) and wheat flakes (wholemeal). Millet flakes (1.1 mg/g d.m.), and rice flakes (1.2 mg/g d.m.) had the lowest content of tannins, which may be a result of high degree of processing.
The tannins determination, as well as other inhibitors, should be a part of the determination of mineral composition as all these factors affect the bioavailability of mico- and macroelements from food product. A product could be a good source of some minerals, but the significant content of taninns (or other inhibitors) would limit their bioavailability.