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High-performance liquid chromatography with diode array detection (HPLC-DAD) was used to study the stability of individual anthocyanins during preparation of raspberry sugar jam and sugar-low jam at high temperatures (90, 95, 100 and 105 °C).
The preparation of sugar jam implied 60% of fruit puree, 30% of saccharose, 9.8% of glucose and 0.2% of commercially available pectin. The preparation of sugar-low jam implied 94.2% of fruit puree, 5% of saccharose and 0.8% of commercially available pectin. Acidified methanol was used for anthocyanin extraction.
Several anthocyanins, all derivatives of cyanidin, were identified: cyanidin-3-sophoroside (cy-3-soph), cyanidin-3-glucoside (cy-3-glu) and cyanidin-3-rutinoside (cy-3-ru). Cy-3-soph was the most abundant, followed by cy-3-glu and cy-3-ru.
Greater stability of all individual anthocyanins was observed in sugar-low jam. The lowest loss of cy-3-soph, cy-3-glu and cy-3-ru was measured after 5 minutes of cooking at 90°C, yielding 35.6%, 38.4% and 29.6% in sugar jam and 13.4%, 24.6% and 11.7% in sugar-low jam. The greatest loss of cy-3-soph, cy-3-glu and cy-3-ru was observed after 30 minutes of cooking at 105 °C, yielding 74.5%, 81.1% and 71.7% in sugar jam and 44.2%, 55.1% and 42.6% in sugar-low jam.
Apparently, the presence of larger amount of sugar had negative effect on stability of anthocyanins in raspberry jam. This fact is in agreement with the research of de Rosso and Mercandante[1] where it has been shown that the addition of sugars had a negative effect on the stability of anthocyanins from tropical fruits.
All anthocyanins exibited greater stability towards thermal degradation in sugar-low jam. Cy-3-soph and cy-3-ru have shown relatively equable stability in sugar-low jam. However, the difference in their stability is more notable in sugar jam, where cy-3-ru was more stable. Cy-3-glu was the least stable in both jam types.
Obtained results are in accordance with previously reported literature data where cy-3-glu was identified as the most unstable pigment during preparation and storage of raspberry jam[2]. Also, cy-3-soph has been identified as the most abundant and the most stable pigment in raspberry juice and wine, while cy-3-glu was the least stable and the most reactive pigment, which undergoes polymerisation faster than all other anthocyanins[3].
References:
[1] V.V. de Rosso, A.Z. Mercadante, Innov. Food Sci. Emerg. Technol., 8, 2007, 347–352.
[2] C. García-Viguera, P. Zafrilla, F. Artes, F. Romero, P. Abellán, F.A. Tomás-Barberán, J. Sci. Food Agric., 78, 1998, 565-573.
[3] A. Rommel, D.A. Heatherbell, R.E. Wrolstad, J. Food Sci., 55, 1990, 1011-1017.
Keywords: cyanidin, raspberry, jam
