黑果枸杞色素在水溶液中的降解动力学及护色剂的筛选

Degradation Kinetics of Pigments from Lycium ruthenicum in Aqueous Solution and Screening of Their Color Fixatives

以-定时间内黑果枸杞水溶液紫外-可见吸收光谱Aλmax的变化为参数,用多个动力学模型进行拟合,以建立降解动力学方程;通过比较不同添加剂对黑果枸杞水溶液的紫外-可见吸收光谱及Aλmax随时间的变化情况筛选护色剂.结果表明：黑果枸杞色素水溶液的降解动力学基本符合Weibull模型;添加量为0.4～80.0 mg/mL的柠檬酸对黑果枸杞色素有稳定作用,可使溶液颜色变为桃红色;添加量为4.0～80.0 mg/mL的抗坏血酸无护色作用,且使降解规律有所改变（基本符合Baker-Lonsdale模型）;添加量为250.0 mg/mL以上的NaCl对色素有稳定作用,且能使溶液保持紫色;钙离子和多元醇类物质无护色作用;硼酸使其褪色速率变慢,体积分数为50%的乙醇则加快其褪色,提示黑果枸杞色素的降解机理可能为非酶途径,而与邻二酚羟基有关.

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 therapid degradation of the purple pigment from Lycium ruthenicu （PLR） in aqueous solution, this work aimed to explore thedegradation mechanism of PLR and to improve its stability. Optimal degradation kinetics and appropriate color fixativesfor PLR were investigated by determining the changes of its UV-Vis absorption spectrum and absorbance at the maximumwavelength （Aλmax） and fitting the changes in Aλmax to several models. The results indicated that： （1） the degradation of PLRin aqueous solution followed the Weibull model basically; （2） 0.4–80.0 mg/mL citric acid was beneficial to the stabilizationof PLR while it could change its color from purple to peach; （3） 4.0–80.0 mg/mL ascorbic acid could not prevent thedegradation of PLR, and it changed the degradation kinetics to Baker-Lonsdale model; （4） sodium chloride at higherconcentrations （250.0 mg/mL or above） could have a stabilizing effect on PLR; （5） additives such as calcium or polyolswere not helpful for improving the stability of PLR. It could be supposed that ortho-diphenolic group rather than plantenzyme could be the main factor responsible for the degradation of PLR, due to slower fading when adding boric acid whencompared with 50% ethanol.