Abstract
The content of anthocyanins in fruits (Sambucus nigra. Vaccinium myrtillus. Aronia melanocarpa) and in some fruit (berry) products was determined by differential spectrophotometry, a method recommended by AOAC International (former Association of Official Analytical Chemists). The method takes advantage of the reversible pH-dependent transformation of the colour to the colourless form of anthocyanins. The procedure and evaluation were refined to allow measurements of incompletely specified anthocyanin mixtures. Parameters of the determination (buffer composition, pH, stabilisation of samples, reference standards) were optimised. Using the modified method, anthocyanins in various matrices (fruits, syrups, wines) were measured with the aim to explain possible losses of these active substances during processing and/or storage of fruit products. Real samples of commercial products recommended conventionally as a valuable source of antioxidants were analysed and in some of them, only low levels of anthocyanins were found. In a model arrangement, anthocyanins in the skin and the pulp of Sambucus nigra fruits were extracted separately. In all samples of various cultivars, anthocyanins were present predominantly in the skin (up to 90% of the total content). Considering this, among other factors, a suitable extraction technology might improve the quality of berry products substantially.
Slovak abstract
Obsah anthokyanů v plodech (Sambucus nigra. Vaccinium myrtillus. Aronia melanocarpa) a v některych produktech z plodů byl stanoven diferenčni spektrofotometrii, metodou doporučenou AOAC International (dřivějši Associace oficialnich analytickych chemiků). Metoda využiva reverzibilni transformace barevne formy anthokyanů na bezbarvou v zavislosti na pH. Postup i způsob hodnoceni byly upraveny tak, aby umožnily měřeni i u ne zcela přesně definovanych směsi anthokyanů. Byly optimalizovany podminky stanoveni (složeni pufrů, pH, stabilizace vzorků, referenčni standardy). Pomoci modifikovane metody byly změřeny anthokyany v různych matricich (plody, sirupy, vino) s cilem vysvětlit možne ztraty aktivnich latek při zpracovani plodů a/nebo uchovavani produktů. Byly analyzovany vzorky vyrobků dostupnych v obchodni siti a doporučovanych obvykle jako cenny zdroj antioxidantů - v některych byl nalezen jen maly obsah anthokyanů. V modelovem uspořadani byly odděleně extrahovany anthokyany ze slupek a dužniny plodů Sambucus nigra. Ve všech vzorcich z různych kultivarů byly anthokyany přitomny převažně ve slupkach (až 90 % celkoveho obsahu). Tyto i dalši faktory je nutno brat v uvahu při vyvoji vhodne technologie, ktera by mohla podstatně zlepšit kvalitu vyrobků z plodů.
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