Abstract:

Lycium ruthenicum is widely distributed in the Qinghai-Tibet Plateau, and its fruits are rich in anthocyanins, 80%
of which is petunidin-3-O-rutinoside (trans-p-coumaroyl)-5-O-glucoside, an ortho-diphenolic compound. Considering the
rapid degradation of the purple pigment from Lycium ruthenicu (PLR) in aqueous solution, this work aimed to explore the
degradation mechanism of PLR and to improve its stability. Optimal degradation kinetics and appropriate color fixatives
for PLR were investigated by determining the changes of its UV-Vis absorption spectrum and absorbance at the maximum
wavelength (Aλmax) and fitting the changes in Aλmax to several models. The results indicated that: (1) the degradation of PLR
in aqueous solution followed the Weibull model basically; (2) 0.4–80.0 mg/mL citric acid was beneficial to the stabilization
of PLR while it could change its color from purple to peach; (3) 4.0–80.0 mg/mL ascorbic acid could not prevent the
degradation of PLR, and it changed the degradation kinetics to Baker-Lonsdale model; (4) sodium chloride at higher
concentrations (250.0 mg/mL or above) could have a stabilizing effect on PLR; (5) additives such as calcium or polyols
were not helpful for improving the stability of PLR. It could be supposed that ortho-diphenolic group rather than plant
enzyme could be the main factor responsible for the degradation of PLR, due to slower fading when adding boric acid when
compared with 50% ethanol.

Key words: Lycium ruthenicum, anthocyanins, degradation, kinetic models, color protection