ศูนย์นวัตกรรมเทคโนโลยีหลังการเก็บเกี่ยว

Colour stability of anthocyanins in aqueous solutions at various pH values

Kjell Torskangerpoll and Øyvind M. Andersen

Food Chemistry, Volume 89, Issue 3, February 2005, Pages 427-440

2005

บทคัดย่อ

This study focuses o­n the impact of anthocyanin structures such as 5-glucosidic substitution and aromatic acylation o­n anthocyanin, colour and stability at various pH values. Two concentrations (0.05 and 0.15 mM) of cyanidin 3-glucoside (1), cyanidin 3-(2’’-glucosylglucoside)-5-glucoside (2), and cyanidin 3-(2’’-(2’’’-sinapoylglucosyl)-6’’-sinapoylglucoside)-5-glucoside (3) in aqueous solutions were studied at fourteen pH levels between 1.1 and 10.5 during a 98 day period at 10 °C. The three pigments represent the structural variation of many anthocyanins isolated from fruitsand vegetables. Colours were expressed by the CIELAB coordinates h_ab, (hue angle), C* (chroma=saturation), and L* (lightness), as well as by visible absorption maxima ( l_max) and molar absorption coefficients (e). Limitations of using o­nly spectral parameters, such asl_max ande, to express colour variations, were revealed. Pigment 2 was more unstable than 1 at most pH values, showing lower C* and higher L* values after storage for o­nly hours in neutral and weakly acid solutions. Pigment 3 showed higher colour stability than the nonacylated forms at all pH values but pH 1.1, where all pigments retained their colours in the storage period, and in the most alkaline solutions, where all pigments experienced dramatic colour changes. Of potential importance for some food products, in solutions with pH 4.1 and 5.1, 3 maintained nearly the same h_ab, C*, and L* values during the whole measuring period (98 days), in contrast to pigments 1 and 2. The hue angle shift towards bluish tones in freshly made samples of anthocyanins with 5-glucosidic substitution, were amplified with aromatic acylation (3) throughout the entire pH range except pH 10.5. The variations in the results emphasizes the importance of structure for anthocyanin properties in fresh and processedfruitsand vegetables.